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In this work, the effect of using baffles and vortex generators on the cooling performance of a gas turbine combustion chamber is numerically investigated. The RNG k-ɛ model is utilized in order to simulate the flow turbulence. The effects of baffles and vortex generator pitch, hydraulic diameter and bypass ratio on the Nusselt number and friction coefficient at different Reynolds number are studied. The cooling performance of applying baffles and vortex generators are also evaluated and compared based on the Performance Evaluation Criterion (PEC). The numerical results are verified with available experimental data. The results show that the pitch increment results in the decrement of the Nusselt number and the wall friction coefficient due to the lower vortices generation and the turbulence kinetic energy dissipation. Also, the Nusselt number is increased by increasing both the bypass ratio and the hydraulic diameter. It is also found that vortex generators and baffles improve the cooling performance of the gas turbine combustion chamber by 18.8% and 26% respectively through decreasing the external wall temperature.

The demand of energy saving and loss mitigation in modern industry gives rise to drag reduction techniques such as micro groove/riblet ever since the last century. Plenty of studies are conducted under straight flow condition showing relevance between drag reduction and flow features. However, the same issue has not been studied adequately for rotational flows, which is typical in turbopumps. In this paper, two-dimensional numerical simulations of rotating disks are performed together with verification experiments to investigate drag reduction effect of micro riblet under rotational flow condition. The numerical results show that riblets with certain dimensions can lessen the resistant torque by a maximum of 8.46% and the drag reduction efficiency depends on rotational Reynolds number and riblet dimensions. Meanwhile, the distributions of static pressure and swirl velocity on surfaces are changed and near-wall turbulence intensity is tranquilized by riblets which are considered as the main reasons to the diminish of drag. Finally, the relevance of vortexes inside riblets to swirl wall shear stress and torque is demonstrated revealing that the configuration of riblets plays an important role in cutting resistance. The results of this paper can be a supplement for the investigation of micro groove/riblet drag reduction mechanism.

API plan 31 uses a cyclone separator that taps a small portion of discharge line process liquid for mechanical seal cooling process. Despite its simplicity, this piping plan requires comprehensive designing process to ensure its performances (flow rate to mechanical seal and pressure drop) are satisfactory. In this research, API 31 cyclone separator geometrical parameters (length cylinder, conical and vortex finder and radius overflow and underflow) effects onto pressure drop and seal flow rate are investigated using numerical method via ANSYS FLUENT software. It is found that increasing overflow and underflow radius and length of cylinder and conical decrease pressure drop by 15.94%, 24.82%, 20.30% and 11.42% respectively. Increasing vortex finder length meanwhile increases pressure drop by 7.77%. Meanwhile, increasing radius overflow and length of vortex finder increase flow rate to seal by 43.79% and 9.63% respectively. Increasing radius underflow and length of cylinder and conical reduces flow rate to seal by 71.92%, 6.41% and 8.93% respectively. It is also observed that a generalization of a particular cyclone separator geometry is not always applicable as it depends on the cyclone separator base design itself where in this case all geometrical factors are significant to pressure drop and flow to seal.

The novel autonomous rolling performance is realized by the pair of pectoral fins of a three-dimensional(3-D) bionic dolphin in this paper numerically. 3-D Navier-Stokes equations are employed to simulate the viscous fluid around the bionic dolphin. The effect of self-rolling manoeuvrability is explored using the dynamic mesh technology and user-defined function (UDF). By varying the parameter ratios, the interaction of flexible pectoral fins is divided into two motion modes, amplitude differential and frequency differential mode. As the primary driving source, the differential motion of a pair of pectoral fins can effectively provide the rolling torque, and the trajectory of the entire rolling process is approximately the clockwise spiral. The results demonstrate that the rolling angular velocity and driving torque in the steady state can be improved by increasing parameter ratios, and the rolling efficiency can reach the maximum under the optimal parameter ratio. Meanwhile, different parameter ratios do not affect the rolling radius of the self-rolling dolphin. The evolution process around the pair of pectoral fins is shown by the flow structures in self-rolling swimming, reasonably revealing that self-rolling locomotion is produced by the pressure and wake vortices surrounding the pair of pectoral fins, and the wake structure depends primarily on the variation of parameter ratio. It properly turns out that the application of the pair of pectoral fins can realize the self-rolling performance through parameter differential modes.

This paper presents a procedure for the estimation of propeller effective wakes in oblique flows. It shows how a recently developed method for controlling coupling errors can be applied to analyze propellers operating in off-design conditions. The approach allows the use of fast potential flow methods for the representation of the propeller in the context of viscous flow solvers and works accurately for a wide range of advance numbers and incidence angles with a minimum computational cost. The new method makes it possible to disclose flow phenomena on the effective wake that were hidden in conventional approaches of effective wake simulation. Different application cases are analyzed, such as a propeller-shaft configuration in inclined flow, a pod propulsor in an oblique inflow, and a ship hull advancing at a yaw angle. A dipole-like distortion on the effective wake is unmasked for a uniform flow incident to a propeller mounted on an inclined shaft. The flow component perpendicular to the axis is found to be responsible for the distortion. The effect of the direction of propeller rotation on the effective wake is illustrated for a single-shaft ship moving at a yaw angle. In particular, keel vortices are either attracted to or repelled from the propeller disk depending on the sign of the yaw angle or alternatively on that of the propeller rotation.

Abstract A measurement technique for recording convective heat transfer coefficient and adiabatic film cooling effectiveness in demanding environments with highly curved surfaces and limited optical access, such as turbomachinery, is presented. Thermography and tailor-made flexible heating foils are used in conjunction with a novel multistep calibration and data reduction method. This method compensates for sensor drift, angle dependence of surface emissivity and window transmissivity, heat flux inhomogeneity, and conductive losses. The 2D infrared images are mapped onto the 3D curved surfaces and overlapped, creating surface maps of heat transfer coefficient and film cooling effectiveness covering areas significantly larger than the window size. The measurement technique’s capability is demonstrated in a sector-cascade test rig of a turbine center frame (TCF), an inherent component of modern two-spool turbofan engines. The horseshoe vortices were found to play a major role for the thermal integrity of turbine center frames, as they lead to a local increase in heat transfer, and at the same instance, to a reduction of film cooling effectiveness. It was also found that the horseshoe vortices lift off from the curved surface at 50% hub length, resulting in a pair of counter-rotating vortices. The measurement technique was validated by comparing the data against flat plate correlations and also by the linear relation between temperature difference and heat flux. This study is complemented with an extensive error and uncertainty analysis. Article highlights This paper presents an accurate measurement technique for heat transfer and film cooling on 3D curved surfaces with limited optical access using flexible tailor-made heating foils, infrared thermography and a high-fidelity multistep calibration process. Graphical abstract

We present a modified version of the ONERA dynamic stall model for improving the prediction of the unsteady forces and load overshoots generated by the shedding of dynamic stall vortices. The modifications include modeling the chord‐axis forces instead of the wind‐axis forces used originally. A novel approach for defining the onset of a dynamic stall is based on the behavior of the chordwise force without correlating the onset empirically. Overshoots in the unsteady aerodynamic loads caused by vortex shedding are modeled by sine‐shaped functions added to the normal force and moment. The onset and duration of these pulses are empirically described in the time domain for convenient use in time‐marching simulations. The modified dynamic stall model is calibrated using a genetic algorithm and compared to experimental data of different airfoils relevant to wind turbine applications. The results show an excellent correlation with the experimental data, particularly in deep dynamic stall, which are characterized by large fluctuations in the aerodynamic loads.

Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) and ocean (waterspout). To better understand the flow nature and topology, this experimental study explores the development of vortex breakdown (VB) in a lab-scale swirling flow of two immiscible fluids filling a vertical cylindrical container. The rotating bottom disk drives the circulation of both fluids while the sidewall is stationary. The container can be either sealed with the still top disk (SC) or open (OC). As the rotation strength (Re) increases, a new circulation cell occurs in each fluid—the dual VB. In case SC, VB first emerges in the lower fluid at Re = 475 and then in the upper fluid at Re = 746. In case OC, VB first emerges in the upper fluid at Re = 524 and then in the lower fluid at Re = 538. The flow remains steady and axisymmetric with the interface and the free surface being just slightly deformed in the studied range of Re. Such two-VB swirling flows can provide efficient mixing in aerial or two-fluid bioreactors.

The aim of this work is to study the working processes of burning the low-quality fuels, namely, the saw dust in the swirling-type furnaces with an opposite twisted motion of the air. The goal was achieved using the physical and mathematical modeling of the flows interaction. The article presented the results of numerical study of aerodynamic characteristics of burning the saw dust in the swirling-type furnace with the opposite twisted air flows. For the research, the facility was used for the saw dust burning with the air supply into the lower and upper zones of burning. The most essential result of the work was modeling of the working process at the ratio of the flows of the primary air and secondary air without the fuel admixture, equal to 0.2. The tangential rate of the flow changed according to the horizontal sections from 3-5 m/s to 40-42 m/s and with respect to the furnace height from 51 m/s to 30 m/s. The average angular rate of the mixture changed relatively the furnace height in the ranges of 171-500 l/s to 100—300 l/s. The significance of the results obtained consists in determination of the possibility of increasing the efficiency of the work of the furnace facilities at the expense of the introduction of the primary and secondary air flows. In this situation, the optimal ratio of consumptions of primary and secondary air was 0.2. Thus, in this work the consumption of primary air was 1.285 kg/s, the consumption of the secondary air was 0.255 kg/s.

Research shows that the surface shape of rotary liquid depends on the rotation mode. Mode A is that when the container wall rotates the liquid, the rotating liquid surface is paraboloid. Mode B is that when the rotor in the center of the container rotates the liquid, the rotating liquid surface is vortex. Based on the paraboloid formed by the mode A, the identity between the liquid level parameter and the wall slope K (K ≠ 0) is derived. When K → ∞, with the increase of the container angular spin rate, the liquid level parameter changes are infinite, the liquid level change and volume relationship are fixed. When K > 0, the container is a cylinder with a large upper part and a small lower part and the liquid level parameter changes are limited, and the limit ratio between the liquid level parameters is + 1. In addition, through the vortex experiment by the mode B, it is concluded that the vortex curve can be regarded as composed of three parabolas: the center triggering part, the rising part, and the edge attenuation part. Different from the mode A, the liquid level change and volume relationship caused by the vortex formed by the mode B are both variables. According to the experimental results, the influences of container inner diameter, initial liquid level, rotor size, and rotor speed on the vortex characteristics are discussed in detail. At the same time, based on the experiment, the liquid level change and volume relationship caused by the formation of the vortex are deduced under the ideal condition when a stable liquid surface is formed by the vortex.

This paper studies the flame dynamics near lean blowout (LBO) conditions in a stratified swirl burner. The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions. In the experiments, only the pilot flame works with four different equivalent ratios. It is found that as the flame changes from stable combustion to near LBO, the flame macrostructure changes from V-shape to M-shape. Meanwhile, a characteristic frequency of 405 Hz is found in the spectrum of heat release signal. The closer to LBO, the higher amplitude is found at the frequency peak. Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame. Large-eddy simulations (LESs) via OpenFOAM reproduce the flame dynamics near LBO, which agrees with the experimental results. LESs provide more insights into the flow fields, showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction. This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO. The heat release signal is also found can be used as a candidate precursor for LBO.

The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities. In this work, the oblique-mode breakdown, as one of the most available transition mechanisms, is studied using the nonlinear parabolized stability equations (NPSE) with consideration of the thermal-chemical non-equilibrium effects. The flow over a blunt cone is computed at a free-stream Mach-number of 15. The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture. It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient. In comparison to the CPG flow, the TCNE effects destabilize the second mode and push upstream the N factor envelope. The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.

This contribution describes experimental and numerical research of an unsteady behaviour of a flow in an end-wall region of a linear nozzle cascade. Effects of compressibility ($$M_\mathrm {2,is}$$ M 2 , is ) and inlet flow angle ($$\alpha _1$$ α 1 ) were investigated. Reynolds number ($$Re_\mathrm {2,is}$$ R e 2 , is $$=8.5\times 10^5$$ = 8.5 × 10 5 ) was held constant for all tested cases. Unsteady pressure measurement was performed at the blade mid-span in the identical position $${\mathfrak {s}}$$ s to obtain reference data. Surface flow visualizations were performed as well as the steady pressure measurement to support conclusions obtained from the unsteady measurements. Comparison of the surface Mach number distributions obtained from the experiments and from the numerical simulations are presented. Flow visualizations are then compared with calculated limiting streamlines on the blade suction surface. It was shown, that the flow structures in the end-wall region were not affected by the primary flow at the blade mid-span, even when the shock wave formed. This conclusion was made from the experimental, numerical, steady as well as unsteady points of view. Three significant frequencies in the power spectra suggested that there was a periodical interaction between the vortex structures in the end-wall region. Based on the data analyses, anisotropic turbulence was observed in the cascade.

Recently, the requirement for cooling capacity decreased when the driving energy changed from liquid fuel to lithium batteries. Therefore, the structure and location of the forecabin could be adjusted based on the aerodynamic performance. The current study conducted a significant number of simulations in order to find out the effects of the internal flow through forecabin in an Ahmed body. The following conclusions have been identified:1, The flow through the forecabin would always increase the resistance of the entire body, and the drag coefficient increases, on average, by approximately 85%. 2, When the aspect ratio is higher or the position of the inlet opening is lower, the total drag coefficient is lower due to a weaker vortex strength, a simpler vortex structure and a relatively simple flow. 3, The existence of the forecabin will largely increase the oscillation frequency of the flow field by approximately 15 times compared to the original Ahmed model. Finally, the high drag coefficient moment always appears to be due to the formation of more complex or intense vortex motion. These conclusions can offer useful results and references for the structural design of the front cabin for new energy vehicles.

This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers.

In this study, a hydrogen fuel jet-stabilized combustor is proposed, the combustion flow characteristics are numerically investigated under the conditions of three equivalence ratios (1, 0.37, and 0.22), and the effects of hydrogen flow rate assignment on the combustion flow are also analyzed. The results show that it is easier for the multijet scheme to form a full and stable vortex structure pair in the recirculation zone under lean conditions than the single-jet scheme, and it has a uniform reaction rate to form larger combustion zones, which makes it easier to achieve flame stabilization. The combustion efficiency of two fuel jet schemes is less than 65% when the equivalence ratio is 1, and complete combustion can be achieved under lean conditions; however, the outlet temperature distribution factor (OTDF) is basically the same. For the multijet scheme with an equivalence ratio of 0.22, as the flow rate assigned to the central jet decreases, a stable and full vortex pair is formed in the recirculation zone, and a high-temperature region can be formed under each working condition, but its area decreases with the central jet flow rate. The combustion efficiency in the recirculation zone increases first and then decreases as the central jet flow decreases, and the OTDF decreases with it.

In this study, the low emission combustion technology of Rich-Quench-Lean (RQL) has been applied in Trapped-Vortex Combustor (TVC), and the combinative RQL-TVC shows a promising low emissions performance. By utilizing a quench orifice plate combined with a bluff-body, a lab-scale RQL-TVC was designed. The flow fields of RQL-TVC were measured by 2-D PIV and predicted by 3-D numerical simulation. Flow structures, radial profiles of normalized mean axial velocity, turbulence intensity and mixing level of the quench zone were analyzed. Results reveal that the dual-vortex and the single-vortex flow patterns both exist in cavities and quench zone of RQL-TVC, and the turbulence intensity is strong in the quench zone with some reverse flows. The spiral vortex was discussed by 3-D streamlines and the detail flow structures of the quench zone were analyzed based on the numerical results. The mixing level of the quench zone was determined, and results show that the quench device enhances the mixing level compared with TVC. Combustion efficiency and emissions performance were investigated experimentally, and results demonstrate that RQL-TVC has relatively higher combustion efficiency and lower emission index of CO, UHC and NOx than the same size lab-scale TVC in present work.

The object of study in the article is the vortex effect of temperature separation in a rotating gas flow, which is realized in small-sized vortex energy separators. The subject matter is the models that describe the physical processes of energy conversion in small-sized vortex energy separators as objects of automatic control. The goal is to obtain models of a vortex energy separator reflecting its static and dynamic properties as an automatic control object. The tasks to be solved are: to develop a three-dimensional computer model of a small-sized vortex energy separator which will allow analyzing the parameters of the gas flow and physical processes of energy conversion directly inside the object and obtaining its static characteristics. A linearization method of static characteristics on the interval of input and output values is proposed which will expand the operating range without loss of linearization accuracy. A method of structural-parametric identification based on experimental logarithmic magnitude-frequency characteristics is proposed which will allow for the same set of experimental points to select the structure of the mathematical model of varying complexity depending on the specified accuracy. As a result of the work, the scheme for modeling the automatic control object was formed, consisting of the drive unit, sensor unit, and vortex energy separator, with the reflection of all the obtained operating modes. The methods used are the method of graphic linearization, Laplace transform, structural-parametric identification. The following results were obtained: a computer and linearized mathematical model of the small-sized vortex energy separator as an automatic control object reflecting its properties in the time and frequency domains was obtained. A comparative analysis of the reactions of the model and the real object to the same input action was carried out. Conclusions. The scientific novelty of the results obtained is as follows: 1) multiple graphic linearizations of one static characteristic to use the full range of the operation mode of vortex energy separator, which distinguishes it from the known;2) mathematical model structural-parametric identification for vortex energy separator with the help of known points of the Bode magnitude plots by using the interpolation polynomial and its derivatives graphs.

The issue of providing fuel and energy resources to the population depends to a large extent on the wear of thermal networks, as well as heat-generating equipment, which, accordingly, forces the consumer to abandon the centralized heating supply in favor of decentralized supply. However, low-power heat-generating units for autonomous consumers do not most of the time operate under the rated mode. The most promising way to solve the issue of energy conservation is to improve the utilization rate of fuel and energy resources in heat-generating units for decentralized heating systems that operate under non-stationary regimes. An experimental study of the velocity field of interaction between the coaxial axial direct-flow and external swirling jets has established that the performance efficiency of a heat-generating plant at a change in the thermal load could be improved by controlling the resulting velocity field. For a more even distribution of temperature within the furnace volume, it has been proposed to supply fuel with an oxidizer in the furnace by the axial direct-flow and swirling coaxial jets. It was revealed that at a distance of 2 diameters of the axial branch pipe from the cut there occurs a transverse toroidal vortex. The appearance of such a vortex is explained by the emergence of low-pressure regions due to the different angles of opening of the swirling outer jet and axial direct-flow jet. The considered dependence of change in the gas flow rate at a decrease in power has demonstrated that the gas flow rate in the proposed burner is less than that in analogs (vortex burner or direct-flow burner) by 10‒15% when the power of the burner is reduced. At the same time, the specified advantage is limited to the range of the burner's power of 50‒130kW. The results reported confirm the possibility of controlling the velocity field and temperature distribution when the total fuel and oxidizer flow rate changes within the operational range of low-power heat-generating plants. The correspondence between the temperature field and the velocity field in the interaction of non-isothermal jets has also been shown

This study presents 2-D simulations of a flow-through a sudden expansion/contraction micro-channel with the existence of obstacles. The bottom wall is maintained at constant flux, while the other walls are adiabatic. Rectangular adiabatic obstacles are mounted before the expansion region on the upper and lower wall of the channel used. The finite element method was used to discretize the equations that govern the physical model. Results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the micro-channel for low Reynolds numbers. For higher values and expansion ratios, the vortex separation length increases. The obtained results show that the obstacles have a considerable effect on the dynamics of the flow and enhancement of heat transfer.

Swirl brakes are usually introduced at the seal entrance in industry to improve the seal stability, especially for labyrinth seals suffering low seal clearance and high inlet preswirl ratio. However, how to arrange swirl brakes at the seal entrance to obtain better seal stability retains unknown, such as the axial distance between the brake trailing edge and the first tooth. To this end, the effects of the distance between brakes and the first tooth on the leakage flow rate and seal rotordynamic coefficients were numerically investigated at typical inlet preswirl ratios of 0.45 and 0.8, and the predicted results were in comparison with the results for no-brake configuration. The obtained results disclose that the brake configuration arranged against the first tooth produces lower circumferential velocity in the downstream of the brakes as a result of the larger counter-clockwise vortex moving from the brake trailing edge to the brake leading edge when compared to the brake configuration away from the first tooth. Besides, the dropped circumferential velocity in the downstream of brakes will cause larger pressure fluctuation in the circumferential direction and thus generates larger tangential force to restrain the rotor forward whirl. On the other hand, the effective damping is further increased when the distance between brakes and the first tooth decreases to zero, that is, the crossover frequency is even disappeared at the inlet preswirl ratio of 0.45 and successfully drops from 69.9 Hz to 32.7 Hz at the preswirl ratio of 0.8.

Research on turbulent drag reduction has been limited owing to the limitations of existing parameters used for the identification of vortex structures. As a new and more suitable vortex parameter, Liutex provides a novel research method for turbulence control. We used a channel with a transverse groove structure as the research model and employed large-eddy simulation method based on Liutex to study the influence and mechanism of the transverse groove structure on the watershed. The analysis revealed that the transverse groove structure significantly inhibited the vortex intensity, and this effect diminished with the increase of the normal height. Moreover, the transverse groove structure could maintain the stability of the flow vortex and restrain the hairpin vortex. The fundamental action mechanism of the groove structure pertained to slip condition of the bottom surface along the flow direction, which was essential for conveying the bottom fluid. Furthermore, the transverse groove structure could significantly reduce the overall increase in the vortex intensity in the transition layer, and the fluctuation of the vortex intensity in the logarithmic layer was lower under the action of the groove structure. This case can guide the application of the new vortex identification method in turbulence drag reduction.

Vortex is the dominant flow structure in hydro-energy machinery, and its swirling features are mainly determined by the rigid rotation part of vorticity. In this study, the rigid vorticity transport equation is proposed based on the vorticity decomposition. The vortex spatial evolution is described by the stretching term RST, the dilatation term RDT, the Lamb term RCT and the viscous term RVT. The shape change of a vortex tube is mainly affected by RST and RDT, while vortex production and dissipation are mainly reflected by RCT and RVT. Compared with the traditional vorticity transport equation, this new theoretical tool can distinguish between rigid rotation and shearing motion of local fluids, and it can better reveal the intuitive evolution characteristics of vortical structures. Two cases with clear engineering demands are analysed by using the transport equation, and the results show that it can provide a practical method for the analysis and control of vortical flows in hydro-energy machinery.

This paper aims to numerically investigate violent sloshing in a partially filled three-dimensional (3D) prismatic tank with or without a baffle, further to clarify the suppressing performance of the baffle and the damping mechanism of sloshing. The numerical model is based on a Cartesian grid multiphase flow method, and it is well validated by nonlinear sloshing in a 3D rectangular tank with a vertical baffle. Then, sloshing in an unbaffled and baffled prismatic tank is parametrically studied. The effects of chamfered walls on the resonance frequency and the impact pressure are analyzed. The resonance frequencies for the baffled prismatic tank under different water depths and baffle heights are identified. Moreover, we investigated the effects of the baffle on the impact pressure and the free surface elevation. Further, the free surface elevation, pressure and vortex contours are analyzed to clarify the damping mechanism between the baffle and the fluid.

The clogging of emitters has been considered as one of the most troublesome problems inhibiting the extension of drip irrigation. This paper investigates the flow field of water and behaviour of suspended particles in the trapezoidal labyrinth-channel. Computational Fluid Dynamics methods has been executed on liquid-solid two-phase flow in labyrinth-channel emitters. RNG k-e turbulence model was used to evaluate four types of emitters that have the same characteristics and differ in the elbow width S. This study has shown that as the value of S increases, the maximum velocity in the labyrinth-channel decreases and the number of vortices increases. However, emitter with a high S value are more subtle to clogging. In addition, it was also observed that smaller diameter particles behave best when they pass through the channel and follow the streamline flow. As the particle diameters become larger, the particles tend to leave the mean stream and enter the vortex zones under the force of inertia. So, more suspended particles trapped in the vortex area , more the chances of emitter clogging increase. All of these furthermore confirm that vortex and low speed regions were the main causes leading to emitter clogging.

For flapping micro-air vehicles, periodical aerodynamics in every plunging period is always desired in the design of aircraft controlling system. During the periodic plunges of rigid airfoil, either periodical or non-periodical aerodynamic forces can be generated. Real airfoils are usually flexible so that the effect of flexibility on unsteady characteristics of aerodynamic periodicity should be considered. In this study, a fluid structure interaction analysis is employed to systematically investigate the aerodynamic periodicity of a periodically plunging flexible airfoil. The influences of several dimensionless kinematic and structural parameters on aerodynamic periodicity are investigated. The results show that the aerodynamic periodicity of plunging flexible airfoil qualitatively resembles that of rigid airfoil as the mechanisms contributing to aerodynamic periodicity are kept for airfoil with various flexibilities. However, aerodynamic periodicity at small plunging amplitude and high Reynolds number can be improved as airfoil becomes medium flexible but worsened as airfoil is very flexible. The reason is that the deformation of the airfoil changes the strength and structure of the nearby vortices, thereby leading to weak vortex–vortex and vortex–airfoil interactions. The extent of improvement in aerodynamic periodicity is also found significantly influenced by incoming velocity.

In this paper, the cavitating flow and pressure fluctuation in the tip region were simulated based on Delayed Detached Eddy Simulation (DDES). The high-speed photography and transient pressure measurements were employed to capture the cavitation structures and pressure fluctuation. The numerical results show a reasonable agreement with the available experiments. The maximum errors of head and efficiency are 2.9% and 2.2%. The impeller rotation dominants the tip pressure field, with some obvious high-frequency components induced by the cavitating flow. Increasing the flow rate from 0.8Qopt to 1.2Qopt, the amplitudes of the frequency domain in P2 decrease from 0.13 to 0.08. There are more harmonic-frequency components at 0.8Qopt, including 5BPF, 6BPF, 7BPF. Suction-side-perpendicular cavitating vortices (SSPCVs) appeared in severe cavitation conditions, which leads to the collapse of the triangular cavitation cloud. The spatial-temporal evolution of SSPCV was divided into three stages: Generating stage, Shedding stage, and Dissipating stage. The pressure fluctuates significantly in the flow passage caused by SSPCV. The amplitudes of dominant frequency in P3 vary from 0.031 to 0.089, as the cavitation number decreased from 0.582 to 0.231. In particular, there is an obvious low-frequency N∗ = 0.5 shown in the frequency domains of P2 and P3.

The objective of this study is to construct a regime diagram for laminar flames stabilized behind flame holders with respect to the presence of a recirculation zone (RZ), trend of heat loss to the burner, and flow strain and flame curvature effects. This is achieved by varying the radius of the cylindrical flame holder and the mixture velocity between the flashback limit and the blow-off limit at a fixed equivalence ratio. It is found that for all flame holders, a RZ vortex is not present near the flashback limit. At flashback, flow strain is almost zero and the flame curvature is found to be the main contributor to flame stretch. With increasing mixture velocity, the heat loss to the flame holder decreases for smaller radii and a RZ does not appear till blow-off occurs. For flame holders with radii greater than twice the flame thickness, the heat loss to the flame holder first decreases with increasing mixture velocity without a RZ. A further increase in the mixture velocity does not result in blow-off but instead, a RZ appears behind the flame holder reversing the heat loss trend. In this scenario, flow strain is found to increase significantly and becomes the major contributor to flame stretch, although curvature effects are still present. With the RZ present, the blow-off limits are significantly extended and the stabilization mechanism is altered. The RZ vortex shields the flame base from intense pre-heating resulting from the increase in heat loss to the flame-holder while it provides support to the flame leading edge by recirculation of hot products. The results obtained from this study are used to construct a regime diagram, which offers a broader view of the whole flame stabilization process and its mechanisms.

Supersonic shear layer development affects mixing between the primary and secondary fluids in a supersonic ejector substantially. The splitter plate plays a key role in shear layer development in the near-trailing-edge region. In this paper, supersonic shear layers with various splitter plate thicknesses are calculated and analyzed. Two types of instability modes are found when various splitter plate thicknesses are used. The shock wave strength and absolute unstable region determine the instability modes. Shock waves can limit instability development but an absolute unstable region promotes instability development. Velocity thickness growth rates are found to be the result of the merging process between two or more adjacent vortices in the transition region. The number of vortices that merge depends on the ratio of the vortex shedding and nature frequencies. The velocity thickness growth rates are larger under the local instability mode than under the global instability mode since three vortices merge under the former mode but two vortices merge under the latter. This study may provide a helpful reference for the design of supersonic ejectors.

The dominant vortex structure near the hub in rotor corner separation flow has an important influence on the internal flow of the axial flow rotating machinery. However, the current quantitative research on the key vortical characteristics of the dominant vortex structure in the corner separation flow is still insufficient. The analysis of the dominant vortex structure (horn-like vortex) in an axial flow pump was conducted and found that the average vortex intensity and turbulence eddy dissipation show a gradual weakening trend along the vortex core line from the corner region to the vortex tail under various working conditions. The evolution of the horn-like vortex in a life cycle includes five stages, inception-growth-development-attachment-decay in the typical working condition 0.62Q0. The statistical average frequency of the periodic evolution is about 2.76 times the shaft rotation frequency. The pressure fluctuation near the hub induced by the horn-like vortex increases rapidly and dominates in the flow channel. The average peak-peak value on the impeller outlet section close to the horn-like vortex is about 2.79 times that of the impeller inlet section and should be paid enough attention to.

"Free surface flow is a hydrodynamic problem with a seemingly simple geometric configuration but with a flow topology complicated by the pressure gradient due to the presence of the obstacle, the interaction between the boundary layer and the free surface, turbulence, breaking waves, surface tension effects between water and air. As the ship appendages become more and more used and larger in size, the general understanding of the flow field around the appendages and the junction between them and the hull is a topical issue for naval hydrodynamics. When flowing with a boundary layer, when the streamlines meet a bluff body mounted on a solid flat or curved surface, detachments appear in front of it due to the blocking effect. As a result, vortex structures develop in the fluid, also called horseshoe vortices, the current being one with a completely three-dimensional character, complicated by the interactions between the boundary layer and the vortex structures thus generated. Despite the importance of the topic, the literature records the lack of coherent methods for investigating free surface flow around junctions, the lack of consistent studies on the influence of the inclination of the profile mounted on the body. As a result, this paper aims to systematically study the influence of profile inclination in respect to the support plate."

Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency. The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design. In this study, we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh. Evolution of wake vortices formed by the main wing, flap and horizontal tail was discussed in detail. The horizontal tail vortices are the weakest and dissipate rapidly, whereas the flap vortices are the strongest and induce the tip vortex to merge with them. The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution, height change and movement trajectory of the wake vortices. The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.

A gravity current in a channel at the presence of a triangular obstacle was investigated using LES simulation and the Eulerian approach. The Saffman–Mei equation was also applied to examine the effect of shear-induced lift force on particle deposition. To this end, particles were considered as Lagrangian markers and injected into gravity current. It is important to keep in mind that the interaction between the gravity current and particles was treated as a one-way coupling. The results show that shear-induced lift force prevents particles to deposit at the entrance of channel, where the velocity gradient is high. Furthermore, a reduction in the rate of sediment deposition can be seen again in the vicinity of obstacle due to high velocity gradient. The important result is that the shear-induced lift force has an important role in the cases with considerable velocity gradient in quasi-steady flows and this force can affect the pattern of sedimentation over time. Q criterion is utilized to depict the vortical structures of flow. Vortical structures with larger diameter, that indicate stronger vortexes, has been seen in various sections of channel, especially in the region near the obstacle due to the presence of obstacle.

In this paper we simulated the focusing of left circular polarized beam with a second order phase vortex and a second-order cylindrical vector beam by a gradient index Mikaelian lens. It was shown numerically, that there is an area with a negative Poynting vector projection on Z axis, that can be called an area with backward energy flow. Using a cylindrical hole in the output surface of the lens and optimizing it one can obtain a negative flow, which will be situated in the maximum intensity region, unlike to previous papers, in which such backward energy flow regions were situated in a shadow area. Thereby, this lens will work as an “optical magnet”, it will attract Rayleigh particles (with diameter about 1/20 of the wavelength) to its surface.

We propose a novel turbulence refinement method based on the Rankine vortex model for smoothed particle hydrodynamics (SPH) simulations. Surface details are enhanced by recovering the energy lost due to the lack of the rotation of SPH particles. The Rankine vortex model is used to convert the diffused and stretched angular kinetic energy of particles to the linear kinetic energy of their neighbors. In previous vorticity-based refinement methods, adding more energy than required by the viscous damping effect leads to instability. In contrast, our model naturally prevents the positive feedback effect between the velocity and vorticity fields since the vortex model is designed to alter the velocity without introducing external sources. Experimental results show that our method can recover missing high-frequency details realistically and maintain convergence in both static and highly dynamic scenarios.

This is a rather biased review paper emphasizing the importance of “understanding” of phenomena. This paper's purpose is to inspire young researchers to taste the real charms of research by observing the process of development of mathematical models of vortex‐induced vibration phenomena of cylinders for understanding their essential mechanism. It first discusses the limitations of human abilities and important aspects of research. Then, it emphasizes the close relation between understanding and mathematical models, and five conditions for a desirable mathematical model: simplicity; inclusion of all essential properties; possession of physical meanings; wide scope of application; and possibility of development. It refers to Birkhoff's wake‐oscillator (1953), Funakawa's early‐wake model (1969), Nakamura's 2DOF flutter model (1970), the Hartlen‐Currie model (1970), the Iwan‐Blevins model (1974), Tamura's non‐linear wake‐oscillator model with a variable length (1979), and the Tamura–Shimada model (1987) for combined effects of vortex resonance and galloping. Some recent developments of the Tamura–Shimada model are also introduced. Then, it discusses the necessity of accurate experimental capture of early‐wake behavior and the aerodynamic properties of a target cylinder in a given flow condition for further development of Tamura's model and the Tamura–Shimada model. Finally, the necessity for efforts to understand phenomena are emphasized.

Numerical results are presented from large eddy simulations (LES) of a turbulent flow in an un-baffled stirred vortex reactor. The open source code TrioCFD is employed with a discontinuous front-tr...

International audience; In this work, the unsteady turbulent flow in a four-baffled stirred tank equipped with a Rushton turbine is computed with ANSYS FLUENT (R) using the sliding mesh technique. The POD algorithm is applied first to each mesh zone (fixed and rotating) and, in a novel and original way, to the full 3D CFD data without distinguishing between the stationary and rotating zones. The resulting modes cannot be regarded as spatial modes revealing the underlying flow structure. The POD results showed that 99.9% of the system variance is recovered with the first three modes. The reconstruction of the velocity field from these modes reveals the trailing vortices plus the mean flow. The accuracy of the POD reconstructed flow fields is quantified. The present work is the first evidence of a POD reconstruction of the unsteady turbulent flow performed over the entire 3D domain in a baffled stirred tank.

We study formation of quasi two-dimensional (thin pancakes) vortex structures in three-dimensional flows, and quasi one-dimensional structures in two-dimensional hydrodynamics. These structures are formed at high Reynolds numbers, when their evolution is described at the leading order by the Euler equations for an ideal incompressible fluid. We show numerically and analytically that the compression of these structures and, as a consequence, the increase in their amplitudes is related to the compressibility of the frozen-in-fluid fields: the field of continuously distributed vortex lines in the three-dimensional case and the field of vorticity rotor (divorticity) for two-dimensional flows. We find that the growth of vorticity and divorticity can be considered as a process of breaking of the corresponding fields. At high intensities, the process demonstrates a Kolmogorov-type scaling relating the maximum amplitude with the characteristic width of the structures. The possible role of these coherent structures is analyzed in the formation of the turbulent Kolmogorov spectrum, as well as the Kraichnan spectrum corresponding to a constant flux of enstrophy in the case of two-dimensional turbulence., 45 pages, 17 figures

This study focuses on the investigation of cavitating flow around the benchmark INSEAN E779A model propeller with the main aim of further improving the computational efficiency of the tip vortex cavitation (TVC) modelling by using a commercial CFD solver. Also, the effects of various key computational parameters including, numerical modelling, grid size, timestep, water quality and boundary layer resolution, on the TVC formation and its extension in the propeller slipstream are investigated systematically. The numerical simulations are conducted in uniform and open water conditions using RANS, DES and LES solvers implemented in the commercial CFD code, Start CCM+. In order to achieve the aim of the study, an alternative and new Vorticity-based Adaptive Mesh Refinement (V-AMR) technique is introduced for enhanced modelling of the TVC on the blades and downstream. For the CFD modelling of cavitation, the Schneer Sauer cavitation model based on the Reduced Rayleigh Plesset equation is used for the sheet, tip and hub vortex cavitation. The hydrodynamic results and cavity patterns are validated with the experimental data. The results show that the application of the V-AMR technique further improves the representation of the TVC with minimal increase in computational cost. However, the eddy viscosity at the propeller blade tips increases with applying the V-AMR technique using the RANS solver due to its inherent modelling errors for the solution of the flow inside the tip vortex. This consequently results in an insufficient extension of TVC in the propeller slipstream compared to the predictions by the DES and LES based numerical solvers. Also, the evolution of the TVC is found to be sensitive to the boundary layer resolution when the standard RANS solver is used. The study will help to widen further applications of the CFD methods involving TVC, particularly for propeller induced underwater noise prediction and analysis.

This paper investigates how targeted interference between two well characterized sources of hydrodynamic disturbances can modify the response of premixed bluff body stabilised H 2 / CH 4 flames with and without swirl. We introduce modulations into the Flame Transfer Function (FTF) through hydrodynamic interference between the shedding of vortices/wakes from different shaped bodies upstream of the flame and the vortex roll-up at the flame base caused by acoustic forcing. By placing a set of small diameter cylinders, a streamlined body, or a swirler upstream of the bluff body and varying the distance from the dump plane, the gain and phase of the FTFs could be modulated at targeted frequencies providing a method to suppress thermoacoustic instabilities. We further investigate the flame response which shows that modulations in the fluctuating global heat release rate are caused by linear superposition along the flame front. At frequencies leading to destructive interference, large-scale wrinkling of the flame front occurs which increases the flame surface area but is offset by the simultaneous pinch-off of the flame tip which decreases flame surface area. Their combined effect reduces the amplitude of the fluctuating global heat release rate. At frequencies of constructive interference, large-scale wrinkling of the flame occurs before the flame tip pinches off, leading to an overall increase in the flame surface and amplitude of the fluctuating global heat release rate.

The influence of Reynolds number, roughness and turbulence on the onset of wall stall is up to now not sufficiently understood. To shed some light onto the interdependency of near wall flow with growing swirl component, the simplest “machine” is tested. The apparatus we examine is a circular pipe at rest followed by a rotating co-axial pipe segment. In the sense of a generic experiment this machine represents a very basic model of the inlet of an axial machine. Due to the wall shear stress a swirl boundary layer is formed in the rotating pipe segment, interacting with the axial boundary layer. The evolution of the swirl velocity profile with increasing axial distance from the rotating pipe inlet is measured for various Reynolds numbers, flow numbers and degrees of turbulence by means of Laser Doppler Anemometry. We observe a self-similarity in the swirl velocity profile, for subcritical flow number and develop a scaling law for the velocity distribution in the transition section of a rotating pipe. At critical flow number the boundary layer is separating, resulting in a ring vortex at the inlet of the rotating pipe. Our work fills the gap of previous experimental works, with respect to high Reynolds numbers and low flow numbers. The parameter field we examine is most relevant for turbomachinery application and wall stall. In addition our boundary layer resolution is sufficient to resolve the swirl boundary layer thickness. Only this high resolution enables us to generalize the experimental findings by means of a similarity distribution of the velocity profile within the swirl boundary layer.

Particle image velocimetry measurements have been carried out in a low-pressure turbine cascade operating under unsteady inflow to deeply investigate reduced frequency and flow coefficient effects ...

We have recently shown that premixed CH 4 /air flames anchored behind flame holders can stabilize in two flame stabilization regimes characterised by the presence or absence of a recirculation vortex [1]. Focus of the present work is on the underlying mechanisms governing flames anchored without the presence of a vortex for methane-air flames. We revisit the definition of the flame anchoring location and define a new anchoring location which results from flame stretch considerations rather than heat loss considerations. This location can be unambiguously defined for flame holders of different sizes. It is argued that such an anchoring location is more relevant for flames stabilized behind flame holders with sharp corners and do take into account the multi-dimensional nature of heat transfer with the flame holder as well. A quantitative assessment of heat transfer, stretch and preferential diffusion effects is then carried out at the anchoring location for elucidating their impact on the flame speed as a function of the flame holder size. New insights into flame blow-off, flashback and emergence of a recirculation vortex are obtained as a result of this investigation.

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through wall-resolving large Eddy simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step, experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration and one with the Coriolis force removed, without any other change. This setup allows a very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region, the tip leakage vortex is enlarged and destabilized. Inside the tip gap, the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly. Funding was provided by the Deutsche Forschungsgemeinschaft (DFG), under FR1593/15-1 and MA4922/8-1 within PAK948. The authors would like to acknowledge stimulating discussions with the partners of this project. Computations were performed at the Centre for Information Services and High Performance Computing (ZIH) at TU Dresden.

The effectiveness of synthetic jet actuation on the wingtip vortices produced by an unswept, low aspect ratio, rectangular wing at a chord Reynolds number of 8.16 × 10 4 is experimentally investigated. The synthetic jet is operated at different actuation frequencies and amplitudes in order to investigate five different control cases characterized by different momentum coefficients and dimensionless frequencies, for a comprehensive parametric study. In particular, the instability frequencies (known as Crow and Widnall) characterizing the wingtip vortex dissipation, are chosen among the tested synthetic jet actuation frequencies. A phase-locked stereoscopic particle image velocimetry is employed to analyze the development of the wingtip vortices in the near wake at a distance from the wing trailing edge of 3 chord lengths. The time-averaged results suggest that the synthetic jet actuation greatly affects the wingtip vorticity distribution causing an outward diffusion which increases with the actuation frequency, with a maximum reduction of 46% on the peak value. On the other hand, when the synthetic jet is operated at the Crow instability frequency, the wingtip induced velocity shows its maximum decrease equal to 29% with respect to the baseline case. The phase-averaged analysis reveals a clear relation between the synthetic jet blowing and suction phases and the periodic variation of the vortices features. In correspondence to the blowing phase, the wingtip vortices undergo a huge diffusion and they are characterized by a larger diameter, higher circulation, and lower induced velocity. These findings confirm that this synthetic jet control configuration can represent a useful device to promote the vortex dissipation and reduce the wake vortex hazard.

International audience; Knowledge of the dynamics of wind turbine wakes and its dependence on the incoming boundary layer is fundamental to optimize and control the power production of wind farms. This work aims at investigating the effect of inflow turbulence on the wake of the NREL-5MW wind turbine. Sparsity-Promoting Dynamic Mode Decomposition (SP-DMD) is performed on snapshots extracted from large-eddy simulations of the turbine wake, for detecting the most dynamically-relevant flow structures in the presence or absence of inflow turbulence. We demonstrate that inflow turbulence generated by a precursor simulation radically changes the most dynamically-relevant flow structures. For the laminar-inflow case the DMD modes selected by the SP algorithm have high wavenumbers and are spatially localized. When turbulence is added at the inflow, these high-frequency modes are superseded by low-frequency modes lying in the frequency range of the wake meandering and filling the whole domain, mostly corresponding to those dynamically relevant for the precursor simulation. These results show that, in the presence of inflow turbulence, coherent structures linked to endogenous mechanisms such as tip and root vortices loose their dynamical relevance in favour of those exogenously excited by turbulence, indicating that low-dimensional models of turbine wakes should take into account atmospheric turbulence.

Among all aquatic species, mantas and rays swim by flapping their pectoral fins; this motion is similar to other fishes in terms of efficiency, but it gives better maneuverability and agility in turning. The fin's motion is featured by a traveling wave going opposite to the forward motion, producing a force thanks to momentum conservation. This article aims at understanding the swimming dynamics of rays, focusing on energy efficiency. A computational fluid dynamics (CFD) model of the swimming motion of a cownose ray has been implemented in openfoam, simulating the acceleration of the fish from still to the steady-state velocity using an overset mesh. In this analysis, the one degree-of-freedom dynamics of forward swimming is solved together with the fluid velocity and pressure. The effect of frequency and wavelength of fin motion on thrust, power, and velocity has been investigated and an analysis of the vortices in the wake showed has been performed. The energy efficiency of a self-propelled body has been defined in a novel way and it has been calculated for different motion conditions. The results showed that batoid fishes swim with high energy efficiency and that they are a promising source of inspiration for biomimetic autonomous underwater vehicles.

Electroconvection and gravitational convection are recognized as the primary mechanisms driving overlimiting currents in ion-exchange systems. Here, we use particle image velocimetry (PIV) to characterize the convection on a small piece of a commercially available heterogeneous cation-exchange membrane. We perform chronoamperometric measurements under various experimental conditions and simultaneously record the developed convection at the membrane-electrolyte solution interface using tracking particles. The convection is observed independently in horizontal and vertical planes, capturing flow fields pertinent to electroconvection and gravitational convection. PIV analysis computes velocity vector fields we employ to calculate the volumetric flow rate through a virtual semi-cylindrical wall around the membrane. The volumetric flow rate represents a way how to quantify the intensity of electroconvection. The electroconvection recorded on the horizontal plane manifests itself as a local short-range chaotic whirring localized at the membrane surface superimposed by two long-range counter-current vortices. The volumetric flow rate associated with the two counter-current vortices almost linearly increases with voltage and decreases with increasing concentration. The stagnant points of the vortices localize from 100 to 450 μm away from the membrane. The convection observed on the vertical plane occurs as a result of electroconvection and gravitational convection. We show that gravitational convection eventually dominates and produces an upward-directed intensive flow with similar values of characteristic velocities as the electroconvection. The development of the gravitational convections is approximately one order of magnitude slower (on the order of seconds) than that of electroconvection (on the order of hundreds of milliseconds).

The impact of confinement on a turbulent lean premixed swirl flame is investigated using a finite-volume large-eddy simulation method to solve the compressible Navier-Stokes equations and a combined G-equation progress variable approach to model the flame. The geometry is an experimentally investigated burner by Moeck et al. [Combust. Flame, 159, 2650-2668 (2012)] in which a precessing vortex core (PVC) and a self-excited thermoacoustic instability occur. To analyze the effect of confinement on the M-shaped flame, three configurations are investigated, i.e., an unconfined configuration, a symmetric confined configuration, and a non-symmetric confined configuration. The symmetric confined configuration corresponds to the experimental burner and the numerical results are in good agreement with the measurements. The flow fields of the confined and unconfined configurations differ significantly due to a more pronounced PVC downstream of the injection tube in the confined configurations. The numerical results confirm experimental findings from the literature, i.e., the confinement defines the recirculation zones and the turbulence intensity of the swirling jets. Furthermore, the present results show that the limit-cycle amplitude of the thermoacoustic instability, which occurs in the confined configurations due to a resonant coupling of the flame with the acoustic quarter-wave mode of the combustion chamber, is significantly reduced in the non-symmetric confined configuration. The mode determined by a dynamic mode analysis (DMD) that describes the impact of the acoustic quarter-wave mode on the velocity field only occurs in the symmetric confined configuration. Consequently, a lower coupling of the acoustic oscillations due to the thermoacoustic instability with the flame is evident. The results emphasize the sensitivity of the thermoacoustic instabilities on the confinement configuration and indicate the dependence of their oscillation amplitudes on the location of the swirl flame in the combustion chamber.