Search

An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of secondary flow strengthening the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6–1 to obtain the optimum baffle pitch for 6000

The flow dynamics and attrition characteristics of three air reactor designs are investigated using an Eulerian-Eulerian kinetic theory model. The hydrodynamics of these reactor designs are analyzed to identify the flow regimes in which the particles evolve. The investigated designs, which differ in the configuration of the secondary flow ports, exhibit bubbling and turbulent fluidization regimes in similar spatial regions. The most substantial differences in the hydrodynamics was in the turbulent fluidized regions near the secondary inlets. The mechanical stressing environments undergone by the particles were analyzed using the collision energy spectra, reconstructed using the local flow field properties (i.e. granular temperature and particle number density). The spectra show that the increase in the specific collision power is associated with the regions near the secondary injector ports, which are in a turbulent fluidization regime. A simple analysis relying upon a partitioning of the energy spectrum, showed that attrition rate may be reduced by about 34% over the original design.

The two-stage ejector has been suggested to replace the single-stage ejector geometrical configuration better to utilize the discharge flow’s redundant momentum to induce secondary flow. In this study, the one-dimensional gas dynamic constant rate of momentum change theory has been utilized to model a two-stage ejector along with a single-stage ejector. The proposed theory has been utilized in the computation of geometry and flow parameters of both the ejectors. The commercial computational fluid dynamics tool ANSYS-Fluent 14.0 has been utilized to predict performance and visualize the flow. The performance in terms of entrainment ratio has been compared under on- design and off-design conditions. The result shows that the two-stage ejector configuration has improved (≈57%) entrainment capacity than the single-stage ejector under the on-design condition.

In the present paper, the steady RANS (Reynolds-Averaged Navier-Stokes) simulations based on our independently developed CFD (Computational Fluid Dynamics) solver NUAA-Turbo 2.0, are carried out to investigate the shock wave/tip leakage vortex (SW/TLV) interaction in two representative transonic axial fan rotors, NASA Rotor 67 and NASA Rotor 37. The intent of this study is mainly to verify if an identification method derived from relevant theories is suitable for shock-induced vortex stability in the real engineering environment. As the additional findings, a universal tip vortex model is established and the characteristics of vortex breakdown or not are also summarized under different load levels. To ensure the prediction accuracy of all numerical methods selected in this research, detailed comparisons are made between computational and experimental results before flow analysis. The excellent agreement between the both indicates that the current code is capable of capturing the dominant secondary flow structures and aerodynamic phenomenon, especially the vortex system in tip region and SW/TLV interaction. It is found that three vortical structures such as tip leakage vortex (TLV), shock-induced vortex (SIV), tip separation vortex (TSV) in addition the tip leakage vortex-induced vortex (TLV-IV, which only occurs when the TLV strength increases to a certain extent) frequently exist near the blade tip and then abstracted as a tip vortex model. A stable TLV after passing through the passage shock is commonly characterized by tight rolling-up, slow deceleration and slight expansion. Conversely, the vortex behaves in a breakdown state. The final verification results show that the above two vortex states can be satisfactorily detected by the theoretical discriminant introduced in this work.

In order to maximize the thermal efficiency of shell and coil heat exchangers, substantial research has been done and geometrical modification is one way to improve the exchange of thermal energy between two or more fluids. One of the peculiar features of coiled geometry is that the temperature distribution is highly variable along the circumferential section due to the centrifugal force induced in the fluid. Moreover, most researchers are concentrated on using a shell and single helical coil heat exchanger to enhance the heat transfer rate and thermal efficiency at different operating parameters. Therefore, the aim of this study is to investigate temperature variation ((T-1, T-2, T-3 and T-4) across a shell and single/double coil heat exchanger at different coil pitches, hot water flow rate, and cold-water flow rate along the outer surface of the coil using experimental and numerical analysis. For single and double coil heat exchangers, Computational Fluid Dynamics (CFD) is carried out using pure water with a hot water flow rate ranging between 1-2 l/min for the coil side heat exchanger. For single coil heat exchangers, the numerical analysis findings showed a good agreement with experimental four-temperature measurement results (T-1, T-2, T-3 and T-4) with an error rate of 1.80%, 3.05%, 5.34% and 2.17% respectively. Moreover, in the current double coil analysis, the hot outlet temperature decreased by 3.07% compared to a single coil (baseline case) at a 2.5L/min hot water flow rate. In addition, increasing the coil pitch will increase the contact between the hot fluid and the coil at a constant hot water flow rate and thereby decrease the hot fluid outlet temperature. Finally, a computational analysis was carried out to examine the flow structure inside single and double coil heat exchangers, and the findings indicated that the effect of centrifugal forces in double coil heat exchangers at various coil pitches caused the secondary flow to be substantially reduced. Conclusions An experimental validation and numerical investigation are provided in the present study for a shell and single/double coil heat exchanger and the effect of operating parameters (hot and cold flow rate) on the hot outlet temperature and temperature distributed along coil surface (T-1, T-2, T-3 and T-4) has studied. The experimental and numerical findings showed that the four temperatures (T-1, T-2, T-3, and T-4) were in good agreement. According to the findings of this study, when a single coil is converted into a double coil, the hot outlet temperature and the temperature distributed along the coil surface decreases at high hot water flow rate (2.5 L/min). Also, the results showed that the influence of coil pitch 30, 60 and 90 mm on a double coil heat exchanger was found to have a minimum temperature of 4.80% at p= 90 mm compared to the other two pitch numbers. In addition, the coil parameters (coil pitch and curvature diameter) have a significant impact on secondary flow within the coil. Future research can quantify LMTD and NTU to evaluate shell and double coil heat exchangers.

Erosion has been recognized as one of the major threats for industries involving multiphase transportation pipelines. Within the last decades, effective parameters on wear pattern have been identified. As a result, the (famous) V-shaped erosion profile has been detected for the pipes' elbow section. In this study, CFD is employed to investigate the erosion mechanism on the square duct elbows. A novel erosion pattern has been observed for square ducts in comparison with the pipes. The impact of several parameters (particle and flow velocity, secondary flow, turbulent intensity, particle streamline) has been inspected as well. It has been led to the conclusion that the erosion rate of square ducts is lower than common pipes, especially when either higher flow velocities or bigger particles size are employed.

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

Purpose The heat transfer within a heat exchanger is highly influenced by geometry of the components especially those with hollow structures like tubes. This paper aims to intend toward the study of efficient and optimized heat transfer in the bends of superheater tubes, with different curvature ratio at constant Reynolds Number. Design/methodology/approach The effect of changing curvature ratio on enthalpy of the fluid passing through the superheater tubes for multi-pass system has been studied with the aid of computational fluid dynamics (CFD) using ANSYS 14.0. Initially a superheater tube with two pass system has been examined with different curvature ratios of 1.425, 1.56, 1.71, 1.85 and 1.99. An industry specified curvature ratio of 1.71 with two pass is investigated, and a comparative assessment has been carried out. This is intended toward obtaining an optimized radius of curvature of the bend for enhancement of heat transfer. Findings The results obtained from software simulation revealed that the curvature ratio of 1.85 provides maximum heat transfer to the fluid flowing through the tube with two pass. This result has been found to be consistent with higher number of passes as well. The effect of secondary flow in bends of curvature has also been illustrated in the present work. Research limitations/implications The study of heat transfer in thermodynamic systems is a never-ending process and has to be continued for the upliftment of power plant performances. This study has been conducted on steady flow behavior of the fluid which may be upgraded by carrying out the same in transient mode. The impact of different curvature ratios on some important parameters such as heat transfer coefficients will certainly upgrade the value of research. Originality/value This computational study provided comprehensive information on fluid flow behavior and its effect on heat transfer in bends of curvature of superheater tubes inside the boiler. It also provides information on optimized bend of curvature for efficient heat transfer process.

In this study, the research aims to eliminate the presence of eddies and non-uniformity in the flow distribution and temperature variation of molten steel in the casting cavity by imposing the external magnetic field on the casting cavity. The numerical analysis is performed to analyze the flow and temperature variation in the presence of a magnetic field. The numerical flow solver is developed in the OpenFOAM CFD platform. The governing equations consist of the Navier-Stokes equation coupled with Maxwell’s equations along with the energy equation. The flow of molten steel in the cavity is kept at a fixed Reynolds number of Re = 2000. The magnetic field strength is calculated by Hartmann number (Ha) and is varied in the range of Ha = 0, 100, 300, and 500. A numerical study shows that the presence of the magnetic field assists in the reduction of secondary flow in the cavity and allows the fluid to occupy the entire area, which subsequently causes the uniform distribution of temperature in the cavity.

The oscillating flow is a problem occurring in the stay vane passage of hydro turbines. The improper shape of the stay vane causes wake formation and sheds large eddies in the trailing edge of the stay vane. The wake at the trailing edge of the stay vane produces pressure fluctuation in the stay vane passage, which leads to noise and vibration during the turbine operation. Therefore, the improper shape of the stay vane may cause flow oscillation in the stay vane passage. Thus, a proper shape design of the stay vane considering the oscillating flow is necessary to mitigate the flow instability. Consequently, experiment and CFD analyses showed that the initial stay vane (ISV) shape causes recirculation and pressure fluctuation. An optimum design methodology is adopted to improve the flow behavior around the stay vane. Optimization of the stay vane is also conducted by using two objective functions (turbine efficiency and flow uniformity) and 12 design variables. The optimal stay vane (OSV) shape is attained by a multi-objective genetic algorithm. Finally, the flow behavior in the stay vane passage with ISV and OSV is compared by experiment and CFD analyses. Thus, the flow instabilities are mitigated with OSV. The installation of OSV improved the flow angle distribution, secondary flow, and pressure fluctuation in the Francis hydro turbine.

As flowing film gravity concentrators, spiral separators are extensively used in the processing of numerous minerals. Appropriate design of their cross-sectional geometries has been known as an eff...

Mixing characteristics in two innovative variants of coiled flow inverter, namely, symmetrical compact coiled flow inverter (SCCFI) and asymmetrical compact coiled flow inverter (ACCFI) are assessed against that of standard coiled flow inverter (CFI), through experimental and numerical analysis conducted under diffusion-free laminar flow condition ( 2.35 ≤ N D e ≤ 11.5 ; 7.55 ≤ N Re ≤ 36.96 ) . The experimental study involves the comparison of step input residence time distribution (RTD) curves to examine (i) the narrowing effects with the increase in Dean number until a unique RTD is achieved, and (ii) the effect of bends on narrowing of RTD. Results show that maximum narrowing of RTD is achieved in SCCFI, followed by ACCFI and standard CFI, and the unique RTDs obtained comply with the narrowing trends: SCCFI at NDe = 5.3, ACCFI at NDe = 3.5 and standard CFI at NDe = 3. The experimental trends are interpreted through an elaborate CFD analysis that predicts the secondary flow features as well as RTD curves. The CFD results show Dean vortices and flow inversion intensifying with Dean number that explains the narrowing effect with the increase in Dean number. RTDs obtained at intermediate bends in all the geometries, show the sequential narrowing with increasing number of bends, thus establishing the beneficial role of complete flow inversion on radial mixing.

Realization of the S-duct benefits requires scrutiny of certain phenomena such as swirls, secondary flows, and flow distortion creation which are related to the S-duct due to its physical curvature. The first phase of the study investigated the flow field inside the S-duct. NASA Glenn research center’s S-duct was adopted in this study. Geometry was created in SOLIDWORKS and mesh was done using ICEM CFD. Numerical analysis was carried out in ANSYS Fluent software. A turbulence model named kω-SST was incorporated. Boundary conditions were set so as to match the experimental test done by NASA Glenn research center. Computational results showed a significant agreement with the experiment. The results also affirmed the presence of the secondary flow and flow distortion at the aerodynamic interface plane. The second phase of the study investigated the ability to control the flow and reduce the flow distortion on the engine fan face. Results showed a 10% flow distortion reduction and the secondary flow severity decreased by 16.5% on the aerodynamic interface plane (AIP). Keywords: Active Flow Control (AFC), Aerodynamic Interface Plane (AIP), Flow Distortion, S-duct

Particulate Matter (PM) pollution is an alarming environmental problem and one of the most used PM control devices in industry is fabric filter, with a pulse-jet cleaning system. A better understanding of the flow behavior of such pulse-jets is essential to improve cleaning efficiency and diminish dust emissions. Therefore, the present study aims to analyze the flow patterns of the cleaning pulse of an industrial-scale bag filter, with high-pressure and low-pressure systems, using transient three-dimensional CFD simulations. The results show that the center bags in a row take slightly higher shares of air volume and the larger part of it is due to secondary flow. The simulations also give insights into the degree of centralization of the jets: misalignment is progressively reduced along the purge tube, being less pronounced in the high-pressure than in the low-pressure system. Although the mass flow is higher in the high-pressure system, the distribution of the flow among the bags is relatively uniform and similar for both systems.Implications: This work shows, through simulations, that the behaviour of the air pulse during the cleaning is not uniform. There is a variation of the pulse along the duct, due to the movement of the wave that is formed. Besides wave intensity and pressure, the position and shape of the cleaning nozzle also affects the air pulse.

The performance of an aircraft engine depends on air flow quality at the engine face / the exit of the air-intake also known as aerodynamic inlet plane (AIP). A single-engine aircraft has complex Y-shaped twin air-intake which causes severe flow separation, distortion and flow non-uniformity at the AIP. The present study compares the efficacy of slotted synthetic jet and a row of four circular synthetic jets attached to inner faces of a twin air-intake to improve aerodynamic performance at the AIP. The results are obtained using computational fluid dynamics. The velocity and vorticity plots show that lateral spread of the circular jets is limited as compared to the slotted jet. The circular jets are found to be weak as compared to slotted jet to prevent separation of main flow occurring in the twin air-intake. The various aerodynamic performance parameters, such as static pressure recovery coefficient, total pressure loss coefficient, distortion coefficient and secondary flow uniformity are compared for both the cases, exhibiting marked improvement in all these parameters. The study demonstrates that the slotted synthetic jets is a better option for controlling flow in twin air-intake as compared to a row of circular synthetic jets.

This paper investigates the flow past two variants of root section profile cascades for a last stage rotor considering three-dimensional flow structures in the near-wall region. Analyses were drawn based on RANS numerical simulations of both variants and on the experimental data obtained by the 3D traversing in the exit flow field of one of the variants. Extent of 3D structures at two different regimes and its influence on aerodynamic characteristics of the blade cascades was assessed. The distributions of Mach number along the profiles were compared with 2D optical measurements and its distortion due to the presence of the sidewall was explored. The interaction between main vortical structures was described and its influence on the loading of the blades, mechanical energy losses and exit flow angle was discussed. The results showed that for a front loaded blade the vortical structures appeared earlier and at a larger extent than for an aft loaded variant. However, due to different Mach number distribution, contribution of end wall flow to the energy losses was lower in the case of the aft loaded variant. The influence of the near wall flow on the loading was found to be rather weak while the deviation of the exit flow angle appeared to be comparable for both of the variants.

The secondary flow downstream of a triple elbow layout was studied experimentally and numerically to visualize the flow behavior under swirling inlet flow conditions. The inlet swirling condition was generated by a swirl generator, consisting of a rotary pipe and honeycomb assembly. The experiments were carried out in turbulent water flow condition at Reynolds number Re = 1 × 104 and inlet swirl intensity S = 1. Ultrasonic measurements were taken at four locations downstream of the third elbow. The two-dimensional velocity field of the flow field was measured using the phased array ultrasonic velocity profiler technique to evaluate the flow field with separation. Furthermore, a numerical simulation was performed and its results were compared with the experimental data. The numerical result was obtained by solving three-dimensional, Reynolds-averaged Navier-Stokes equations with the renormalization group k-e turbulence model. The experimental results confirmed that the swirling flow condition modified the size of the separation region downstream of the third elbow. A qualitative comparison between the experimental and CFD simulation results of the averaged velocity field downstream of the third elbow showed similar tendency on reverse flow.

Elbow pipes are important components for ice slurry pipeline transport. However, the flow characteristics of ice slurry in elbow are far from fully being understood, especially the influence of ice particle kinetics on ice particle size distribution (PSD). This study is intended to provide a better understanding of the behavior of ice slurry flow in elbow pipe. A CFD-PBM coupled model is employed to investigate the flow characteristics of ice slurry in horizontal 90° elbow pipe. The quadrature method of moments is utilized to solve the population balance equations. Based on the revised model, the flow characteristics of ice slurry in the horizontal 90° elbow pipe are investigated. The simulation results show that in the range of calculations, the pressure drop of elbow pipe is increased with the increase of velocity and ice packing fraction (IPF). An adverse pressure gradient is formed due to the change in flow direction. The emergence of secondary flow is caused by the centrifugal force. It makes the ice particles gather on the outer wall of the elbow section. The ice diameter increases along the flow direction due to the aggregation. The evolution of particle size distribution (PSD) is not significant. However, aggregation and stratification cannot be ignored in the process of long distance transport of ice slurry. The results are of significance for guiding the safety design and operation of ice slurry transportation.

A numerical investigation of the mixing performance and fluid flow in a new split and recombine (SAR) Y−Uβ micromixer is presented in this work. A parameter called connecting angle βis varied from 0° to 90° to analyze the effect on the SAR process and mixing performance. Thenumerical data shows that the SAR process strongly depends on the connecting angle (β) and maximum efficiency (93%) can be achieved when the value of β is 45°. The Y−U45° the mixer also offers higher efficiency and lower pressure drop than a known SAR ‘H−C’ mixer irrespective of Reynolds numbers. The split and recombine process, the influence of secondary flow, and pressure drop characteristics at various Reynolds numbers are also studied. In addition, mixing effectiveness is also computed, and among all examined mixers, Y−U45° is by far the best performing one.

This study aimed to optimize the secondary flow injection from an axial gas turbine casing. For this purpose, the ANSYS-CFX software was used to simulate GE-E3 turbines that generated performance curves for the turbine. Comparing these curves with empirical results showed an acceptable agreement. The variables used for design optimization include the injection's angle, mass flow rate, diameter, and location. Efficiency was the main objective function of the study. The parameters were optimized using response surface methodology (RSM). Moreover, the sensitivity of output parameters to input variables was investigated. Overall, the observations indicated that the injection mass flow rate was the most influential factor in turbine efficiency.

Gas turbines widely applied to power generation and aerospace propulsion systems are continuously enhanced in efficiency for the reduction of environmental load. The energy recovery efficiency from working fluid in a turbine component constituting gas turbines can be enhanced by the increase of turbine blade loading. However, the increase of turbine blade loading inevitably intensifies the secondary flows, and consequently increases the associated loss generation. The development of the passage vortex is strongly influenced by the pitchwise pressure gradient on the endwall in the cascade passage. In addition, a practical high pressure turbine stage is generally driven under transonic flow conditions where the shock wave strongly influences the pressure distribution on the endwall. Therefore, it becomes very important to clarify the effects of the shock wave formation on the secondary flow behavior in order to increase the turbine blade loading without the deterioration of efficiency. In this study, the two-dimensional and the three-dimensional transonic flows in the HS1A linear turbine cascade at the design incidence angle were analyzed numerically by using the commercial CFD code with the assumption of steady compressible flow. The isentropic exit Mach number was varied from the subsonic to the supersonic conditions in order to examine the effects of development of shock wave caused by the increase of exit Mach number on the secondary flow behavior. The increase of exit Mach number induced the shock across the passage and increased its obliqueness. The increase of obliqueness reduced the cross flow on the endwall by moving the local minimum point of static pressure along the suction surface toward the trailing edge. As a consequence, the increase of exit Mach number attenuated the passage vortex.

In the scope of the ENPRO II initiative (Energy Efficiency and Process Intensification for the Chemical Industry), a major challenge of process intensification of polymer synthesis in continuous systems is fouling. Pre-mixing is a key aspect to prevent fouling and is achieved through milli and micro structured devices (Bayer et al. 1). While equal volume flow ratios are well investigated in milli and micro systems, asymmetric mixing tasks have received less attention. This paper investigates the dependency of mixing phenomena on different flow rate ratios and modified inlet geometries. A split-and-recombine (SAR) mixer is modified by means of an injection capillary to facilitate the asymmetric mixing task. Asymmetric volume flows of ratios between 1:15 and 1:60 are investigated; the velocity ratios range from 0.5 to 2. The setup is simulated with the Computational Fluid Dynamics (CFD) tool ANSYS®;Fluent. The species equation is solved directly without the use of micro mixing models. The simulation is validated by means of a concentration field in a mixing Tee using Laser-Induced Fluorescence (LIF) with a Confocal Laser Scanning Microscope (CLSM). The three dimensional flow structures and the mixing quality are analyzed as a measure for micro mixing. The calculated concentration fields show good agreement with the experimental results and reveal the secondary flow structures and chaotic advection within the channel. The injection of the small feed stream is found to be very efficient when drawn into the secondary structures, increasing the potential of diffusive mixing. CFD simulations help to understand and locate such structures and improve the mixing performance.

Centrifugal blood pumps are usually designed with secondary flow paths to avoid flow dead zones and reduce the risk of thrombosis. Due to the secondary flow path, the intensity of secondary flows and turbulence in centrifugal blood pumps is generally very high. Conventional design theory is no longer applicable to centrifugal blood pumps with a secondary flow path. Empirical relationships between design variables and performance metrics generally do not exist for this type of blood pump. To date, little scientific study has been published concerning optimization and experimental validation of centrifugal blood pumps with secondary flow paths. Moreover, current hemolysis models are inadequate in an accurate prediction of hemolysis in turbulence. The purpose of this study is to optimize the hydraulic and hemolytic performance of an inhouse centrifugal maglev blood pump with a secondary flow path through variation of major design variables, with a focus on bringing down intensity of turbulence and secondary flows. Starting from a baseline design, through changing design variables such as blade angles, blade thickness, and position of splitter blades. Turbulent intensities have been greatly reduced, the hydraulic and hemolytic performance of the pump model was considerably improved. Computational fluid dynamics (CFD) combined with hemolysis models were mainly used for the evaluation of pump performance. A hydraulic test was conducted to validate the CFD regarding the hydraulic performance. Collectively, these results shed light on the impact of major design variables on the performance of modern centrifugal blood pumps with a secondary flow path.

The influences of the profiles and cross-sectional areas of glottal aperture on the upper respiratory airway are investigated using an idealized cast-based mouth-throat model and three dimensional computational fluid dynamics (CFD). The open source CFD code OpenFOAM is employed. The transient flows are modeled using the very-large eddy simulation with the Smagorinsky sub-grid scale (SGS) model. Five different shapes of glottis are considered, including circular glottis with 100 %, 75 % and 50 % cross-sectional area and elliptic glottis with 75 % and 50 % cross-sectional area. Both instantaneous and averaged flow fields are analyzed. It is found that the variations of glottis have great impacts on the properties of downstream flow fields such as the secondary flow, laryngeal jet, recirculation zone, turbulent kinetic energy, and vortex. Evident impacts are observed in the region within 6 tracheal diameters downstream of the glottis. The profile of the glottis has more impacts on the laryngeal shape, while the cross-sectional area has more impacts on velocity of the laryngeal jet and turbulent intensity. It is concluded that both the glottal areas and profiles are critical for an idealized geometrical mouth-throat model.

This article provides a summarizing account of the results obtained in the current collabora-tive work of four research institutes concerning near-wall flow in turbomachinery. Specific questions regarding the influences of boundary layer development on blades and endwalls as well as loss mech-anisms due to secondary flow are investigated. These address skewness, periodical distortion, wake interaction and heat transfer, among others. Several test rigs with modifiable configurations are used for the experimental investigations including an axial low speed compressor, an axial high-speed wind tunnel, and an axial low-speed turbine. Approved stationary and time resolving measurements techniques are applied in combination with custom hot-film sensor-arrays. The experiments are complemented by URANS simulations, and one group focusses on turbulence-resolving simulations to elucidate the specific impact of rotation. Juxtaposing and interlacing their results the four groups provide a broad picture of the underlying phenomena, ranging from compressors to turbines, from isothermal to non-adiabatic, and from incompressible to compressible flows. The investigations reported in this article were conducted within the framework of the joint research project “Near-Wall Flow in Turbomachinery Cascades” which was funded and supported by the Deutsche Forschungsgemeinschaft (DFG) under grant number PAK 948. The responsibility for the contents of this publication lies entirely by the authors.

Inertial focusing has been widely used in particle/cell separation and flow cytometry. In this work we presented an improved inertial focusing chip, consisting of an annular channel with obstacles distributed on the inner wall. Two types of secondary flows were generated and then superposed, thus enhanced the impact on particles. The simulation and experimental results showed that the enhanced secondary flow allowed precise focusing of particles and improved the focusing efficiency. The developed chip achieved a focusing width of ≈11.3 µm for 10.7 µm particles with a flow rate of ≈300 µL/min. This inertial focusing chip could be used for high-sensitive optical detection, especially for flow cytometry

In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generating flow-induced vibration in the secondary flow region. A simplified U-tube model is proposed in this study to apply for experiment and its counterpart computation. Using the commercial code, ANSYS-CFX, we first verified the Moody chart, comparing the straight pipe theory with the results derived from CFD (computational fluid dynamics) analysis. Considering the virtual mass of fluid, we computed the major modes with the low natural frequencies through the comparison with impact hammer test, and then investigated the effect of pump flow in the frequency domain using FFT (fast Fourier transform) analysis of the experimental data. Using two-way fluid-structure interaction module in the CFD code, we studied the influence on mean flow rate to generate the displacement data. A feasible CFD method has been setup in this research that could be applied potentially in the field of nuclear thermal-hydraulics. Keywords: Fluid-structure interaction, U-tube, Steam generator, CFD, Flow-induced vibration

Three different computational fluid dynamics (CFD) methods are assessed for their ability to predict topological flow features in idealized street canyons with uneven building heights. Mean velocity-fields from step-up (i.e., a high-rise building downwind of a low-rise building) and step-down (i.e., a low-rise building downwind of a high-rise building) street canyons are evaluated against high-spatial-resolution wind-tunnel data. Each method represents a different level of flow physics using: a mass-conserving model entitled Quick Urban & Industrial Complex wind model (QUIC-URB), a Reynolds-averaged Navier-Stokes (RANS) model, and a large-eddy simulation (LES) model. A new metric that represents the equally weighted trade-off between accuracy and efficiency is introduced to evaluate the CFD methods’ capabilities to capture major-flow topological features in uneven building height street canyons. For step-up street canyons, all three methods qualitatively predict primary topological features, however, none simultaneously capture all secondary features. For step-up street canyons and step-down street canyons with narrow-streets, QUIC-URB captures most of the primary flow topological features including stagnation and saddle points and rooftop recirculation zones. RANS captures primary vortices for step-up street canyons and step-down street canyons with wide-streets. LES is computationally costly but it is the only method that successfully predicts secondary flow topological characteristics for step-down street canyons with wide-streets. When examining our trade-off metric, QUIC-URB has the highest score for step-up street canyons, while QUIC-URB and RANS have equally high trade-off scores for step-down street canyons with narrow-streets, and QUIC-URB and LES have nearly equal trade-off scores for step-down street canyons with wide-streets.

The influence of the elbow lifting angle, airflow velocity and solid mass flow rate on particle flow regimes in lifting elbows has been characterized by an Euler-Lagrange four-way coupling method. The computational fluid dynamics (CFD) and discrete element method (DEM) were used for modeling in this paper. The effect of particle-wall collisions on particle motion was considered by adopting a modified Hertz-Mindlin (no slip) model. An orthogonal design method, to significantly reduce the number of the schemes, was used in this paper to discriminate the significant effects of three independent variables on pressure drops in the lifting elbow. The effect of the secondary flow on pressure drops, volume fractions and solid concentrations is discussed in the results section. The results indicated that the pressure drop increased gradually with increasing airflow velocity and solid mass flow rate; however, there was an optimal lifting angle at which the pressure drop was the smallest. For a 90° elbow, the maximum collision region of the particles on the inner wall of the elbow depended only on the ratio of the radius of curvature to the diameter of the pipe and was independent of the airflow velocity and particle concentration.

The air intake design system of the dorsal intake combined with the S-shaped inlet has been widely used in various combat aircraft due to its good stealth characteristics. In this paper, the numerical simulation of the flow characteristic and influence law of various parameters for a typical air intake design with dorsal S-shaped inlet was carried out using the in-house large-scale parallel computational fluid dynamics (CFD) solver. Firstly, the numerical method was introduced and the solver was preliminarily validated by the well-known RAE M2192 inlet model. Then, the numerical calculation of the target air intake design was conducted and the distribution of shockwave at the entrance area, the second flow in the inlet and the flow at the exit section plane were analyzed in proper order. In addition, the influence of the bump height and lip sweep angles on the inlet performance was also studied. The simulation results show that the unique S-shaped design in the inlet will result in flow separation and secondary flow, ultimately causing total pressure loss, and different external geometry parameters have a great influence on the inlet performance. Within a certain range, proper reduction of the bump height or lip sweep angle can improve the inlet performance.

Three-dimensional CFD simulations carried to evaluate mixing performance of two designs of micromixers namely RB-TSAR and EB-TSAR. The results of flow physics analysis indicate that the interfacial area between the two flow fluids can be enhanced by creating a flow in transverse direction with the help of split and recombination of fluid streams by placing baffles in diffuser shaped mixing elements along the axial direction. Further, the simulation results indicate that at inlet Reynolds number below 1, the molecular diffusion is the most dominant mechanism of mixing, and the mixing index is almost the same for all cases. However at Re > 5, the secondary flow influencing the mixing process dramatically and thus mixing index is increased. The results also reveal that baffles can break the fluid streams, produce fluid convection and increase the contact area of the fluid by folding and deflecting which in turn helps to improve the mixing index. The split and recombination of the fluid streams and separation vortices play vital role in enhancing the mixing performance. The design configurations studied here showed mixing index higher than 0.85 for the Re in the range from 10 to 50.

The ability to regulate secondary flow is significant for efficient particle/cell focusing. Microfluidic technologies have accomplished impressive progress in particle/cell manipulation with the help of the Dean effect. Herein, we explored blood cell focusing with the ultra-low aspect ratio inertial microfluidic system which uses the geometric confinement to enhance the secondary flows to different degrees. Introducing a series of micro-bars in the spiral microchannels accelerates the secondary flow, which can greatly enhance highly-efficient particle/cell focusing under various flow rates. Further, plasma extraction can be successfully achieved from 15× diluted whole blood in an easy-to-use (without the assistance of sheath fluid and complex manufacturing of multi-layer structure), high and wide flow rates (1–5 mL/min, exhibiting no parallel construction design), long-term (at least 60 min), stable (processing at least 300 mL blood samples with consistent efficiency), and highly-efficient (99.99% blood cell rejection ratio) manner. Compared with previously-reported technologies, the engineering strategy of secondary flow in our designed dimension-confined spiral channel provides a balanced overall performance for plasma separation pointing to ease-to-fabrication, insensitive to flow-rate, high throughput and operation efficiency.

The respiration flow pattern plays a key role in fluid flow, heat and mass transfer in human lung airway. To reveal the complex flow pattern within human lung multiple-generation airway, both the steady inspiration and expiration flows are comprehensively studied using laser Doppler velocimetry technique and computational fluid dynamics method for an idealized human tracheobronchial three-generation airway model at two flow rates, corresponding to an adult male breathing under light activity and moderate exercise conditions, respectively. The comparison of mainstream velocity between the measurements and simulations are generally good. Both of the inspiration and expiration flows are heavily influenced by the combination of geometrical bifurcating/merging, local wall curvature, limited generation length and multi-generation interaction. The mainstream flow is non-uniform and behaves as skewed, double-peaked and M-shaped patterns. The secondary flow is complex and characteristic of Dean-type two-vortex, four-vortex, six-vortex and eight-vortex patterns. This work is of scientific significance for a deep understanding of respiratory flow physics and of certain application values for clinical diagnosis and remedy of respiratory deceases.

A numerical investigation is carried out on a centrifugal pump to show the effect of the impeller blades number on the pump performance. Three different impellers with 5, 7, and 9 blades are tested numerically to determine the optimum blades number at rotational speed of 2800 rpm. Fluent 6.3.1 CFD commercial code is used to perform this work. It is found that the head coefficient ‘Ψyt’ and the efficiency ‘ηhyd’ are higher for the case of the impeller with 7 blades than that for the two cases of 5 and 9 blades. The losses decrease by increasing the blades number due to the reduction of the secondary flow for a certain limit.Then it increases again because the friction losses in the impeller and the mixing losses after the impeller yield an increment in the total losses in the region of the vaneless diffuser. This could be a result of the increasing number of the impeller channels. Keywords: Centrifugal pump, Blade number, CFD, Impeller losses, Mixing losses

An ejector aiming at an 80 kW polymer electrolyte membrane fuel cell system designed based on the Sokolov 1-D ejector mode is evaluated numerically and experimentally. A two-dimensional axisymmetric model for the ejector is established based on the Shear Stress Transport model and the Re-Normalization Group model and validated by comparing simulated results and experimental data. Effects of the ejector's mixing chamber diameter and diffusion chamber angle and humidity of the secondary flow on its performance are investigated by a Computational Fluid Dynamics method. The results show that the primary mass flow rate presents a linear relationship with the primary pressure and that the Re-Normalization Group model is more accurate than the Shear Stress Transport model in predicting the ejector's performance. When the diffusion chamber angle is 11 ° and 13 ° , the ejector exhibits the best performances. The mixing chamber diameter and the secondary flow humidity significantly influence entertainment ratio and hydrogen recirculation of the ejector.

The major objective of the present study is to evaluate the performance of a range of turbulent eddy viscosity models in the prediction of macro-parameters (flow coefficient (CQ) and force coefficient (CF)), for certain types of valve, including the conic valve, the disk valves, and the compensated valve. This has been achieved by comparison of numerical predictions with experimental measurements available in the literature. The examined turbulence models include most of the available turbulent eddy viscosity models in STAR-CCM+ 12.04. They are the standard k-e model, realizable k-e model, k-ω-sst model, V2F model, EB k-e model and the Lag EB k-e models. The low-Re turbulence models (k-ω-sst, V2F, EB k-e and Lag EB k-e) perform worse than the high-Re models (standard k-e and realizable k-e). For the conic valve, the performance of different turbulent models varies little; the standard k-e model shows a marginal advantage over the others. The performance of the turbulence models changed greatly, however, for prediction of CQ and CF of the disk and compensated valves. In general, the realizable k-e model is demonstrated to be a robust choice for both valve types. Although the EB k-e may marginally outperform it in the prediction of CF at large disk valve opening. The effects of the unknown entry flow and initialization conditions are also studied. The predictions are more sensitive to the entry flow condition when the valve opening is large. Additionally, the uncertainties caused by unknown entry conditions are comparable to overall modelling errors in some cases. For flow systems with multiple stable flow-states coexisting in the flow domain, the output of the numerical models can also be affected by the initialization conditions. When the streamline curvature and secondary flow is modest like conical valve flow, the nonlinear modification of the standard k-e model and k-ω-sst model, as well as the curvature correction in the realizable k-e model, will not have visible effects on the numerical prediction. Once the strong streamline curvature and secondary flow exit in the domain, such as the disk valve flow, the non-linear modification of the standard k-e model will greatly improve the numerical outputs, however, the non-linear modifications of k-ω-sst model only have minor effects. Moreover, the curvature correction in the realizable k-e model will jeopardise the accuracy of outputs in the same case.

Experimental test of a 3D parameterized vane cascade with non-axisymmetric endwall was conducted by using the particle image velocimetry (PIV) and five-hole probe. Both the straight annular cascade with axisymmetric endwall (denoted by Ref) and the negatively bowed cascade with non-axisymmetric endwall (denoted by Opt) were tested. Here, the Opt design was obtained through optimization based on Computational Fluid Dynamics (CFD), by combining the techniques of section profiling, compound lean and non-axisymmetric endwall [1] . The results showed that, the pressure distributions of blade surface at 10%, 50% and 90% spans of CFD results and experimental data are in good agreement. The trends of total pressure coefficient at cascade outlet (denoted by C p t ) and outlet flow angle (denoted by α 1 ) were well matched; the C p t of Opt design was shown increased by 0.47%, and 0.41% in experiment and CFD simulations, respectively. The contours of C p t showed that the profile loss of Opt design is significantly reduced and the secondary loss region gets closer to hub and shroud. By tracking the secondary vortices near the hub of cascades, the affected area of secondary flow of Opt design was confirmed to be smaller when compared to that of the Ref design; but the size of passage vortex near the cascade exit was increased. The results of PIV and five-hole probe were consistent; they both confirmed that the combined parameterization of both blade and endwalls is effective in reducing the affected area of secondary flow and the profile loss of the low-aspect-ratio vane cascade.

Purpose The purpose of this paper is to study the transient cavitation process in torque converters with a particular focus on cavitation suppression with a passive flow control technique. Design/methodology/approach The transient fluid field in a torque converter was simulated by RANS-based computational fluid dynamics (CFD) in a full three-dimensional (3D) model. A homogeneous Rayleigh–Plesset cavitation model was used to simulate the transient cavitation process and the results were validated with test data. Various secondary flow passages (SFP) were applied to the stator blade. The cavitation behavior and hydrodynamic performance were simulated and compared to investigate the effect of SFP geometries on cavitation suppression. Findings Presented results show that cavitation in the torque converter is highly unstable at stall operating condition because of the combination of a high incidence angle and high flow velocity. The addition of an SFP to the stator blade produces a disruption of the re-entrant jet and reduces the overall degree of cavitation, consequently inhibiting the unstable cavitation and reducing performance degradation. Originality/value This paper provides unique insights into the complicated transient cavitation flow patterns found in torque converters and introduces effective passive flow control techniques useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.

Lateral intakes are used for water transmission and distribution on farms and irrigation networks. In present study, the flow field within a rectangular lateral intake in subcritical flow regime is numerically simulated in a three-dimensional. In this analysis of CFD, turbulence of flow field is simulated using standard $$k - \varepsilon$$ , and RNG $$k - \varepsilon$$ turbulence models, and changes of free surface is simulated by volume of fluid scheme. Comparison between CFD and experimental results showed that the numerical model simulated the free surface and velocity field with high accuracy. Root mean square error for longitudinal and transverse profiles of the flow free surface in the main channel is respectively calculated as 0.132% and 0.094%. Based on simulation results, with the flow progress towards the downstream diversion channel, the secondary circulation cell is developed. A relation is presented for calculating strength of the secondary flow with a nonlinear regression method and using Minitab software. Also, a relation is proposed for calculating the flow energy head within the downstream channel and lateral channel (E3, E2) compared to the flow energy head in the upstream intake (E1).

Numerical experiments were conducted to investigate the effect of leading edge modifications via fillet shapes near vane/blade-endwall juncture in a transonic environment within the highly loaded high pressure turbine stage. The investigated fillet shapes were designed based on geometric parameters: leading edge radius and included angle. The geometrical modifications were achieved to achieve variation in fillet radii at vane/blade endwall juncture along the stream-wise direction, namely variable fillet and constant fillet. Further their influences were studied in both nozzle guide vane and rotor passage secondary flow field. Computational Fluid Dynamics (CFD) method was used to resolve the flow features inside the turbine passage for planar and fillet cases. The presented data highlight the secondary flow features and their behavior using topological properties of flow field aided with the streamline and iso-contour plots. The flow-field results show a significant reduction in the total pressure losses associated with the horse shoe vortex near the leading edge region as the fillet radii are varied. Overall in both vane and rotor passages, variable fillet outperforms the constant fillet by reducing the penetration length of three-dimensional regimes along its span, mitigating the boundary layer growth and improving the loss coefficients.

An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of the strength of secondary flow on the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6 to 1 to obtain the optimum baffle pitch for 6000 < Re < 14000. The maximum thermohydraulic performance parameter (THPP) is obtained as 2.28 for Rp = 0.75 at Re = 6000. With this optimum Rp, the impact of gaps at leading, at trailing, and at both leading and trailing apices is studied as three different configurations. Maximum heat transfer enhancement of 2.47 times is obtained for multiple inclined baffles with the gap at trailing apex for Re = 14000 with a corresponding increment of 3.07 times in friction factor (f). Maximum THPP is obtained as 2.69 for gap at the trailing apex for Re = 6000. With lower exergy losses, the present SAH design has higher exergetic efficiency, collector efficiency and is cost-effective compared to ribbed rectangular SAH.

The presence of a gap between guide vanes and top-bottom covers and rotating-stationary geometries induces the secondary flows in Francis turbines. The secondary flow developed in the clearance gap of guide vanes induces the leakage vortex that travels towards turbine downstream affecting the runner. Likewise, secondary flows from the gap between rotor-stator component enter the upper and lower labyrinth region. Francis turbines when operated with the sediment-laden water, sediment contained flows affect these gaps thus increasing the size of the gap and increasing the leakage flow. This work examines the secondary flows developing at these locations of Francis turbine and consequent sediment erosion effects. A reference Francis turbine of Bhilangana III Hydropower Plant (HPP), India with a specific speed (Ns=85.4) severely affected by sediment erosion problem was selected for this study. All the components of the turbine were modelled and a reference numerical model was developed. This numerical model was validated with the numerical uncertainty measurement and with the experimental results. Erosion at guide vanes were due to the development of leakage flow inside the guide vane clearance gaps. At the runner inlet, erosion was mainly due to leakage vortex from clearance gap and leakage flow from rotor-stator gaps.

A novel CFD modeling approach was developed to investigate the hydrodynamics and mass transfer in a gas–liquid slug flowing through microscale coil and coiled flow inverter channels. One straight slug model was formulated by adding a virtual centrifugal body force. The model was validated in terms of the helicity and secondary flow magnitude. The secondary flow magnitude was shown to be a power function of the Dean number, and a new correlation was proposed. The mass transfer across the interface was compared to that obtained in previous studies. The new model described the temporal and spatial distribution of species in the slug reasonably well. The volumetric mass transfer coefficient kLa in the coil was found to be 1.5 times higher than that in the straight channel, and the enhancement in kLa reached a maximum at a modified Dean number of 1.2.

Organic Rankine cycle (ORC) systems are a readily available technology to convert thermal energy from renewable- and waste heat sources into electricity. However, their thermal performance is relatively low due to the low temperature of the available heat sources, but more importantly, due to the low efficiency of the employed expander. Designing the turboexpander is exceptionally challenging, because the flow field is highly supersonic and unsteady, and since the expansion takes place in the highly non-ideal dense-vapor region. In this work, we perform unprecedented three-dimensional unsteady simulations of several high-expansion cantilever ORC turbines to highlight distinctive loss mechanisms. The simulations indicate strong unsteady effects in the rotor blade passage, as a result of unsteady propagating shock waves interacting with viscous wakes and boundary layers. Moreover, the flow field in the rotor blade passage is strongly affected by three-dimensional secondary flow features and a sharp expansion in the shroud region at the inlet of the rotor blade. These span-wise mechanisms and unsteady flow interactions introduce irreversible losses which must be taken into account for designing highly efficient ORC expanders.

The performance of the ejector relies on the geometrical parameters and the fluid phase state. Although the optimization of geometries of the ejector has been conducted in previous studies, the influence of different optimization sequence of geometric parameters was ignored in previous literatures. To close the knowledge gap, the goal of this paper is to investigate whether different optimization sequences affect the ejector performance and whether the ejector performance is the same under different optimization sequences after multiple rounds of optimization. Therefore, three geometrical parameters, namely the constant-pressure mixing chamber length (Lpm), the constant-area mixing chamber length (Lam) and diameter (Dam), are selected for the optimization study; besides, multi-round optimization with six optimization sequences of these three parameters is conducted by CFD simulations under four different combinations of primary flow liquid volume fraction (LVF1) and secondary flow liquid volume fraction (LVF2) (LVF1 = 0 plus LVF2 = 0, LVF1 = 0 plus LVF2 = 0.06, LVF1 = 0.06 plus LVF2 = 0, LVF1 = 0.06 plus LVF2 = 0.06) for the first time. The results showed that: (1) for each LVF combination, the three optimal parameters and corresponding maximum ER produced by one round optimization of six different optimization sequences are evidently different; (2) after multiple rounds of optimization, for LVF1 = 0 plus LVF2 = 0 or LVF1 = 0.06 plus LVF2 = 0.06, ultimate optimal geometrical parameters and maximum ER are the same with each other for six optimization sequences, however, for LVF1 = 0 plus LVF2 = 0.06 or LVF1 = 0.06 plus LVF2 = 0, each of them still has two different ultimate maximum ER; (4) for those four combinations, different sequence takes different optimization rounds, recommended sequences are Dam → Lam → Lpm (S6), Lpm → Lam → Dam (S1) or Lpm → Dam → Lam (S2), and Lam → Lpm → Dam (S3) and Dam → Lam → Lpm, respectively; and (5) the ultimate optimal parameters and maximum ER in four combinations differ significantly because they are largely dependent on the inlet fluid states.

The Y-shaped elbow is used as a connecting pipe between the buffer and the lift pipe in the deep-sea mining system. After being mixed with seawater in the Y-shaped elbow, nodule particles are lifted to the sea surface mining ship via the lift pump. In this paper, we employ a computational fluid dynamics and discrete element coupled method (CFD-DEM) to study the characteristics of particle transport in the Y-shaped elbow. Considering a large diameter of the particles, we discuss the behavior of particles and fluid under different conveying velocities. In addition, the simulation was verified based on the experiment. The results show that the simulation agrees well with the experiment. On this basis, the distribution and motion characteristics of the particles in the Y-shaped elbow were obtained. The interaction between fluid and particles is also discussed. These findings suggest that the particles can be successfully transported when the pump runs at medium to high frequencies. The particles are basically moving along the pipe wall and slower than the fluid flow. Moreover, it was found that the particle motions are more complex with the increasing of conveying velocities, and it is closely related to the secondary flow of fluid. Some suggestions on the actual particle transportation can be put forward based on the research in this paper.

Walking and running are common types of physical activities people do in day to day living, to improve health and physical fitness or for recreation. During a physical activity, rate and depth of breathing increase because working muscles need extra oxygen in order to produce energy. In this study, computational fluid dynamics (CFD) simulations were used to investigate respiratory airflow flow dynamics in human upper airways response to walking and running. The numerical simulations were done in a realistic CT-scan airway model using ANSYS Fluent 19.0 software. Flow fields were characterized numerical and flow patterns were investigated in the airway model during inspiration and expiration in response to walking and running. The axial velocity distribution and secondary flow patterns were analyzed response to the two physical activities at different cross-sections of the airway model. The maximum velocity, wall pressure, and wall shear stress values for running were respectively 3.2, 9.4 and 5.9 times higher than that of walking during inspiration. More mixing of streamlines was observed during running than walking because of the occurrence of greater turbulence. More skewed flows at airway curvatures were observed at the inspiration than expiration. The result of this study supported the fact that running is a more intensive activity than walking from respiratory dynamics point of view.

Abstract Helically coiled tubes are widely used in industry to enhance heat and mass transfer in the laminar flow regime, due to their secondary flow pattern. In this study, tomographic particle image velocimetry (tomo-PIV) is used in a horizontally coiled helical tube to systematically acquire 3C-3D velocity fields for Reynolds numbers ranging from 20 to 1400 and Dean numbers from 8 to 567. The velocity field evaluations are performed using two different approaches: time-averaged velocity field calculation from instantaneous velocity fields and velocity field determination by cross-correlation from an ensemble of instantaneous reconstructed volumes. Equivalent velocity field accuracy is achieved in both velocity approaches when the flow can be considered stationary. Moreover, numerical simulations were carried out in the same geometry at the same flow conditions and were validated against the experimental 3C-3D data sets. The simulation results show good agreement with the measured velocities, offering the possibility of parametric studies and design optimization. To the authors’ best knowledge, this is the first systematic experimental investigation of a helical coil flow by means of 3C-3D velocity measurements, which results can now be used for validation of numerical models in computational fluid dynamics. Graphic abstract Measured time-averaged velocity visualized by vector-magnitude colour at horizontal and vertical slices (left) and Dean vortices detected by 3D Q-criterion (right) from the time-averaged measurements (purple isosurfaces) and from the simulation (red isosurfaces) inside the helically-coiled tube at Re = 220 and De = 89.

MicroChannel blockage is a common problem in microreactor applications. The principle of inertial aggregation in microchannel is used to analyze the formation of secondary flow and the wall effect of blockage. A heterogeneous microchannel structure combined with expansion and contraction is designed to achieve separation of blockage and solution. Finally, the designed microchannel is compared with the straight tube microchannel which has the same volume by CFD simulations, and the blockage distribution in the microchannel of the expansion-contraction structure is 340% larger than that of the straight tube structure, and the blockages are effectively collected in a predetermined separation position.