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In this study, a cold storage container was simulated with the aim of improving the freezing process through innovative techniques. To accelerate the freezing rate, porous foam was introduced within the storage unit, while water was enhanced by the dispersion of hybrid nanopowders. Additionally, radiative cooling was incorporated as a method to further expedite solidification. The numerical model, validated through the Galerkin method, demonstrated high accuracy and reliability. Results showed a noteworthy decrement in freezing time by about 65.78% when using porous foam, highlighting its role in enhancing thermal conductivity within the system. The incorporation of radiative cooling increased the freezing rate by around 57%, providing further evidence of its effectiveness in speeding up solidification. Moreover, the addition of nanopowders to the H2O mixture resulted in a 4.24% decrease in period time. The prominence of this work lies in its ability to significantly enhance cold energy storage systems by combining multiple advanced techniques. This innovative approach not only improves efficiency but also offers potential applications in fields such as cryogenics and thermal management. [ABSTRACT FROM AUTHOR]

This study introduces an innovative design for cold storage containers featuring wavy outer walls and integrated fins to intensify the diffusion of cold energy throughout the system. The inclusion of fins significantly improves the productivity of the freezing by allowing cold energy to distribute more evenly and rapidly within the storage medium. A secondary method employed to accelerate freezing involves the use of copper oxide nanoparticles, which are dispersed in water. To ensure the validity of the single-phase approximation, the concentration of nanoparticles (ϕ) is kept below 0.045. The study also explores the impact of nanoparticle shape on the material properties, with a focus on two different shapes—blade and cylindrical—and varying the shape factor (m) to assess their influence on freezing efficiency. An implicit modeling technique is employed, utilizing the adaptive mesh. This approach enhances the accuracy of the simulation, with validation results demonstrating strong agreement with expected outcomes. The findings reveal that the introduction of CuO nano-powders can significantly decline the completion time. Specifically, the fastest freezing time achieved was 163.79 s, representing a 27.29% improvement compared to the baseline scenario without additives, where freezing was completed in approximately 225.27 s. Moreover, altering the shape of the nanoparticles further enhances the freezing rate, with blade-shaped particles reducing the freezing time by an additional 6.97% compared to cylindrical particles. [ABSTRACT FROM AUTHOR]

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice. [ABSTRACT FROM AUTHOR]

A test facility was constructed to investigate the flow characteristics of lateral synthetic jets generated by an actuator composed of a cavity, an orifice and a vibrating piezoelectric disc. Subsequently, 3D unsteady numerical simulations were conducted to analyze the formation of the synthetic jets and their dependence on the height of the orifice exit from the outer surface of the cavity. The time-averaged axial velocity was measured and used to validate the numerical results, and the maximum velocity reached approximately 8 m/s. In this work, it was found that the interaction of the vortex tube generated at the edge of the orifice exit and the outer surface of the cavity has a significant impact on the axial velocity distribution and characteristics of the lateral synthetic jets. Based on the experimental data and the numerical results, an attempt has been made to understand the formation of the synthetic jets and their interaction with the outer surface. [ABSTRACT FROM AUTHOR]

Researchers always like to find way for improving the performance of system integrated with PCM. In this paper, the container was combined with fins and PCM was mixed with nanoparticles to obtain quicker discharging process. Two significant variables related to second technique are fraction of additives (ϕ) and their shapes (m). To involve these factors in equations, single phase formulation was applied. Low magnitude of velocity of liquid material in freezing leads to simplification of equations of this transient procedure. Galerkin method which was applied for this modeling has good accommodation with previous publication. As ϕ soars, the solidification time declines from 4802.97s to 4244.61s and 3738.37s when blade shape particles were applied. This means that adding additive can enhance the rate of process about 22.16%. Moreover, augmenting the shape factor to higher level causes time to drop about 5.7%. [ABSTRACT FROM AUTHOR]

Developing and optimizing separators are a challenging task that demands advanced laboratory facilities or costly field assessments. Computational Fluid Dynamics (CFD) simulations can be a prompt and economical alternative. This study aims to find a robust and reliable method to simulate unsteady state two-phase flow in the sophisticated vertical separators connected to plunger pumps using CFD. The unsteady nature of reciprocating pumps and vertical two-phase gas–liquid flow forces the unsteady state boundary condition to the separators. Consequently, to simulate them, the plunger pump was considered a part of geometry, and an unsteady state turbulent two-phase flow was selected for the simulation method. Due to the geometry vastness and complexity of such a problem, the mesh generation method became vital for the convergence and reliability of simulations. Among several mesh generation methods and software, a new MATLAB meshing method developed to generate structural hexahedral mesh proved robust and time-efficient. First, a set of experimental data of a simple separator was used to select, tune and validate the simulation method. Then, a real sample sophisticated separator and a plunger pump were analyzed using the method. Results demonstrated the ability of the model to predict phase separation and motions and its capability for modeling two-phase flow inside the helical, gravitational, and hybrid separators together with a plunger pump. Performing simulation for three up and two down strokes of the plunger showed that after disappearing the initial condition effects, the model represents the same results and separation efficiency for all cycles of plunger movements. [ABSTRACT FROM AUTHOR]

In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an on-design Mach number of 6.0 under incoming wind shear at high altitudes, precisely at an altitude of 30 km with a magnitude speed of 80 m/s. Despite the low intensity of wind shear at high altitudes, the results reveal that wind shear significantly disrupts the inlet/isolator flowfield, affecting the shock wave/boundary layer interaction in the unthrottled state, which drives the separation bubble at the throat to move downstream and then upstream. Moreover, the flowfield behaves as a hysteresis phenomenon under the effect of wind shear, and the total pressure recovery coefficients at the throat and exit of the inlet/isolator increase by approximately 10% to 12%. Furthermore, this research focuses on investigating the impact of wind shear on the behavior of the shock train. Once the inlet/isolator is in a throttled state, wind shear severely impacts the motion of the shock train. When the downstream backpressure is 135 times the incoming pressure (p0), the shock train first moves upstream and gradually couples with a cowl shock wave/boundary layer interaction, resulting in a more significant separation at the throat, and then moves downstream and decouples from the separation bubble at the throat. However, if the downstream backpressure increases to 140 p0, the shock train enlarges the separation bubble, forcing the inlet/isolator to fall into the unstart state, and it cannot be restarted. These findings emphasize the need to consider wind shear effects in the design and operation of hypersonic inlet/isolator. [ABSTRACT FROM AUTHOR]

Flow-induced noise is closely related to the flow characteristics through an adiabatic capillary tube and a transition pipe, most existing methods for suppressing flow-induced noise are passive. An aerating technique is proposed based on the pressure feedback in the transition pipe to actively suppress flowinduced noise. The 3-D simulations of flashing are presented by performing the Schnerr-Sauer cavitation model coupling with the mixture model. For the turbulence model, the large eddy simulation approach is used. With the installation of aerating module, the pressure fluctuation in the transition pipe is weakened significantly, and the phenomenon of bubble collapse is suppressed. Numerical results illustrate that the transient pressure of the monitoring points downstream of the capillary outlet oscillates seriously due to the bubble bursting. The shedding process of the bubble group is observed according to the vaporliquid interface in the transition pipe. In addition, the oscillations of monitored transient pressure are suppressed with the application of aerating module. Then the noise source can be partially reduced actively in essence. This paper is devoted to understanding the two-phase flow characteristics of refrigerants in a transition pipe and presents a practical method to suppress noise near the capillary outlet. [ABSTRACT FROM AUTHOR]

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice.

Unsteady flow simulations were conducted to investigate the flow generated by a synthetic jet actuator in quiescent air. The predicted synthetic jets by 2D axisymmetric and 3D simulations were compared to each other and experimental data to check their accuracy. It was found that the 2D axisymmetric simulations were as accurate as the 3D simulations to predict synthetic jets in quiescent air. Thereafter, three different membrane profiles, namely a simple trigonometric model, a distributed load model and a concentrated load model, have been tested to determine which one is most appropriate to describe the motion of a piezoelectric disc, which was attached to a cavity and was oscillated to generate synthetic jets, using 2D axisymmetric unsteady simulations. Finally, a critical value of Mach number was found in this work for considering the compressibility of air based on the numerical simulations for synthetic jets. [ABSTRACT FROM AUTHOR]

In this paper, unsteady characteristics of a modified vaned-recessed casing treatment with 23.2% rotor blade tip axial chord exposure were studied numerically. The modifications to the traditional vaned-recessed casing treatments were composed of geometrical amendments to the casing treatment's guide vanes and the top of the treated casing. The solid casing and the casing treatment configurations were simulated using the Unsteady Reynolds-Averaged Navier–Stokes equations (URANS), and the results were validated by experimental results. Firstly, standard deviation and frequency analysis were performed to find the sources of unsteadiness. Secondly, velocity components analysis, including velocity triangles, was presented instantaneously to clarify their effects on rotor tip flow fields as well as stall margin improvement. Thirdly, unsteady interactions between the rotor and casing treatment flow fields, including flow structure and pressure distributions, were discussed. In the end, flow streamline patterns, in addition to the physical mechanism of the vaned-recessed casing treatment, were also discussed. The results indicated that unsteadiness plays an important role in the flow mechanism and cannot be ignored. The unsteadiness increases as the mass flow is reduced toward the stall/surge condition. Moreover, the analysis of velocity components demonstrated that the casing treatment has distinct behavior at the last operating points before the onset of the stall for solid casing and casing treatment configurations in terms of axial velocity change. [ABSTRACT FROM AUTHOR]

In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an on-design Mach number of 6.0 under incoming wind shear at high altitudes, precisely at an altitude of 30 km with a magnitude speed of 80 m/s. Despite the low intensity of wind shear at high altitudes, the results reveal that wind shear significantly disrupts the inlet/isolator flowfield, affecting the shock wave/boundary layer interaction in the unthrottled state, which drives the separation bubble at the throat to move downstream and then upstream. Moreover, the flowfield behaves as a hysteresis phenomenon under the effect of wind shear, and the total pressure recovery coefficients at the throat and exit of the inlet/isolator increase by approximately 10% to 12%. Furthermore, this research focuses on investigating the impact of wind shear on the behavior of the shock train. Once the inlet/isolator is in a throttled state, wind shear severely impacts the motion of the shock train. When the downstream backpressure is 135 times the incoming pressure (p0), the shock train first moves upstream and gradually couples with a cowl shock wave/boundary layer interaction, resulting in a more significant separation at the throat, and then moves downstream and decouples from the separation bubble at the throat. However, if the downstream backpressure increases to 140 p0, the shock train enlarges the separation bubble, forcing the inlet/isolator to fall into the unstart state, and it cannot be restarted. These findings emphasize the need to consider wind shear effects in the design and operation of hypersonic inlet/isolator.

Real‐time prediction and dynamic control systems that can adapt to an unsteady environment are necessary for material fabrication processes, especially crystal growth. Recent studies have demonstrated the effectiveness of machine learning in predicting an unsteady crystal growth process, but its wider application is hindered by the large amount of training data required for sufficient accuracy. To address this problem, this study investigates the capability of transfer learning to predict geometric evolution in an unsteady silicon carbide (SiC) solution growth system based on a small amount of data. The performance of transferred models is discussed regarding the effect of the transfer learning method, training data amount, and time step length. The transfer learning strategy yields the same accuracy as that of training from scratch but requires only 20% of the training data. The accuracy is stably inherited through successive time steps, which demonstrates the effectiveness of transfer learning in reducing the required amount of training data for predicting evolution in an unsteady crystal growth process. Moreover, the transferred models trained with relatively more data (no more than 100%) further improve the accuracy inherited from the source model through multiple time steps, which broadens the application scope of transfer learning. [ABSTRACT FROM AUTHOR]

To study the pressure pulsation characteristics of the cryogenic expander, the numerical simulation was performed on the expander hydraulic model by the numerical simulation method. Firstly, external characteristics of expander were obtained by steady numerical simulation. Simulation results were compared with test results, verifying the accuracy of simulation results. The unsteady numerical simulation was performed based on the results of steady numerical simulation.The time-domain plot at different monitoring points of the guide vane and the runner was drawn, and the frequency-domain plot at monitoring points was obtained through fast Fourier transform. The results show that the effect of dominant frequency at the monitoring point of the runner on fluid is as consistent as that of the number of the guide vanes and the effect of dominant frequency at the monitoring point of the guide vanes on fluid is as consistent as that of the number of the runner. The amplitude of the dominant frequency at the monitoring point is related to the point location. When the monitoring point is close to the vaneless area between the guide vane and the runner, the amplitude is larger. The further the distance from the vaneless area is, the smaller the amplitude is, and the smaller the influence of dynamic and static interference between the guide vane and the runner is. The research could provide reference for the design of cryogenic expander.

Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor. However, its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now. To conquer this issue, unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment (ASCT). The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1% of the shaft speed, which is identical to the test data. The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT. The flow structure of the spike inception was investigated at 50% design rotational speed. Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave. Furthermore, it was found that with and without ASCT, the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge, which is different from a fraction of the centrifugal compressor. The resultant phenomenon provides corroborating evidence for that unlike in axial-flow compressor, the addition of ASCT does not change the stall characteristics of the mixed-flow compressor. The flow structure that induced spike inception with ASCT is similar to the case with smooth casing. In the throttling process, tip leakage flow vortex had been involved in the formation of tornado vortices, with one end at the suction side, and the other end at the casing-side. The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex. The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex. These results not only can provide guidance for the design of casing treatment in mixed-flow compressor, but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines. [ABSTRACT FROM AUTHOR]

A test facility was built to investigate the cooling effects of a piezoelectric fan on a heated flat plate in a quiescent atmosphere. The facility consists of a heat source of a thin Ni-Cr foil and a piezoelectric fan for cooling the foil, where the surface temperature on the foil was measured by an IR camera. 3D unsteady numerical simulations were then conducted to analyze the relationship between the jet flow from the piezoelectric fan and the temperature distribution on the heated plate. The measured temperature data was used for validation of the numerical results. Without the fan, the temperature is highest at the center of the plate and lowers toward the plate edge. With the operation of the fan, the temperature at the center of the plate is locally reduced by 28 °C. Based on the experiments and simulations, it is confirmed that the piezoelectric fan is very effective to cool the plate locally. In addition, it was found that the local convective heat transfer coefficient is closely related to the movement of the vortices generated by the fan. • Cooling effects of a piezoelectric fan are analyzed by experiments and simulations. • The piezoelectric fan is very effective to cool the heated surface locally. • The local heat transfer is significantly enhanced by the vortices form the fan tip. • The flow changes quickly but the surface temperature keeps the same during a cycle. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper handles the subject of the modelling and simulation of the flow inside a centrifugal pump through non-cavitating and cavitating conditions. Operating under cavitation state is so perilous to a pump and can considerably reduce its lifetime service. Hence, to provide highly reliable pumps, it is essential to comprehend the inner flow of pumps. The investigated centrifugal pump comprises five backward curved-bladed impeller running at 900 rpm. The modelling process started with an unsteady numerical analysis under non-cavitating conditions to validate the numerical model and the solver comparing with the available testing data. Due to high Reynolds numbers, turbulence effects have been taken into account by unsteady RANS methods using an SST-SAS turbulence model. The obtained pump performances were numerically compared with the experimental ones, and the outcome shows an acceptable agreement between both. The temporal distribution of the internal flow parameters such as pressure and velocity was then studied. Furthermore, basic investigations of cavitating flow around 3D NACA66-MOD profile using a recently developed and validate cavitation model was established. The verification of the numerical simulation validity was based on comparing calculated and experimental results and presented good agreement. Finally, a 3D simulation of the inception of the cavitating pocket inside the centrifugal pump is performed to analyze the impact of the cavitation in the decrease of the head and efficiency.

[Objectives] In order to study the unsteady hydrodynamic performance of turbines under changing current conditions,[Method] this paper uses the Dynamic Fluid Body Interaction(DFBI) method based on an overset grid to simulate the unsteady hydrodynamic performance of turbines under different flow conditions. [Results] The results show that the DFBI method based on an overset grid can realize the monitoring of such transient parameters as speed, torque and flow field in the three stages of starting, acceleration and stabilization of the turbine during start-up. The power coefficient of the turbine has a peak value near the design flow rate of 1.2 m/s. Under dynamic conditions, the average energy efficiency of the turbine is about 0.181, which is about 33% lower than the designed flow rate of 1.2 m/s. [Conclusions] The numerical simulation method used in this paper can monitor the hydrodynamic performance of passively rotating turbines under real current conditions, and changes in the characteristic parameters of the turbine flow field and power output under passive rotation conditions, which can play an important role in guiding actual engineering design.

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ducted fans are widely used in unmanned aerial vehicles due to their high propulsive efficiency and safety. The aerodynamics are complex within the vicinity of the ground, including take-off, landing and hovering. In the present study, the aerodynamic stability of the ducted fan was studied with a modified Moore-Greitzer model to estimate and analyse the stability in ground effect. The model was validated and compared with threedimensional unsteady simulations. The results indicated that the rotating stall occurred for the ducted fan in ground effect. The model results can be used to guide the design and control of the vehicles, to ensure the stability and safety of both the ducted fan and vehicles. [ABSTRACT FROM AUTHOR]

Considering the mass and energy sources carried by the accumulated ice layer, an unsteady heat and mass transfer model of the runback water film on the deicing surface is established to simulate aircraft electro-thermal deicing process. With the extension of the freezing coefficient to the transient calculation, the coupled heat transfer of the runback water and the solid skin is solved at each time step by a temperature-based method. Unsteady numerical simulation is carried out for the electro-thermal deicing system of a NACA 0012 airfoil. The temperature variations with time are in acceptable agreement with the literature data, and the unsteady temperature-based deicing model is verified. The calculation results of temperature, runback water flux and ice thickness on the deicing surface are analyzed at different time points, and it is shown that the unsteady electro-thermal deicing model can capture the main features of the icing, ice melting and re-freezing processes in the transient deicing simulations. [ABSTRACT FROM AUTHOR]

Most physical models for fluid flow and heat transfer obey partial differential equations depending on time and space. Unsteady numerical simulations consist of a considerable number of time steps for which the stability requirement of the explicit time integration has been investigated, while, there is not a suitable method to determine the time step in the computation for fully implicit time scheme and requires a lot of trial and error process. In this paper, a direct approach to estimate the time step in unsteady computation using finite volume method is presented based on characteristic time scale of laminar convective transport phenomena. As an example, this approach is described with buoyant convection in a rectangular pool which is heated due to an electric current generated by an externally applied electric potential difference across the two vertical walls, then, Lorentz force driven convection is considered also. Our theoretical predictions are conducted through full numerical simulations. It is found that the actual time steps in numerical experiments are in good agreement with the scaling analytical predictions. The characteristic time step is deduced and predicted also, not assumed randomly, which provides a basis for the recommendation of the time step for fully implicit time scheme in the finite volume method. This is a key feature that differs from the existing numerical methods. [ABSTRACT FROM AUTHOR]

• A modeling scheme is proposed to solve the difficulty of high temperature test. • The pump loss mechanism for conveying different viscosity medium is proposed. • The relationship between unsteady flow field and pump performance are revealed. Molten salt pumps are key equipment used in solar high-temperature heat transfer and heat storage systems. As it is difficult to use the high-temperature molten salts for experimental tests, and significant changes in the molten salt viscosity affect the pump performance, a modeling scheme is proposed and verified in this study. An unsteady flow field simulation inside the pump is conducted for molten salt pump conveying mediums with different viscosities. To study the unsteady characteristics of the flow field inside the pump, the angle α between the blade and the volute tongue is defined. It is found that the shape of the pressure curve at the volute tongue is related to the medium viscosity as α changes. The position of the blade affects the velocity distribution inside the volute significantly. Moreover, the shapes of the performance curves H - Q , N - Q , η - Q are greatly affected by the viscosity of the molten salt. The mechanism of flow loss with different viscosities mediums inside the pump is revealed. The research results provide an important reference for the further studies of molten salt pump. [ABSTRACT FROM AUTHOR]

Patchy cleaning is one of the principal factors resulting in the reduction of the efficiency and quality of reverse pulse-jet cleaning as well as the service lifetime of filtration units. To resolve the above issues, a new pleated cartridge shape was introduced in this study to improve the cleaning efficiency and quality of pleated filter cartridges. To calculate the transient flow and pressure fields for a simple filtration system with one filter cartridge in the reverse pulse-jet cleaning process, an unsteady computational fluid dynamics model was developed via the commercial computational fluid dynamics software of ANSYS CFX. The transient static pressure fields for filter cartridges under four different pleated cartridge shapes were studied. The conventional cylindrical cartridge was selected as the base-model of filter cartridge and contrasted with other three cartridge shapes. It was found that the convergent–divergent cartridge was able to effectively improve the cleaning performance without the increase of tank pressure. Different pleated cartridge shapes are expected to be able to redistribute the pressure drop across the porous media along the filter height and to improve the flow behavior after pulsing gas releasing from the nozzle. For convergent–divergent cartridge shape, the peak pressure on the inner surface of porous media has an obvious increase and the peak pressure arriving time is earlier than other cases. It shows that the reverse flow has much more competence to remove the dust powder or cake from the porous media. At the same time, the area-averaged pressure drop at the bottom section of the filter has an increase of 50% under the cartridge with a convergent–divergent shape compared to that with a cylindrical shape. It is considered to enhance the cleaning mechanical stress at the bottom section of the filter cartridge. The better cleaning performance was observed in the medium, with 150% increase compared to that with a cylindrical shape. Furthermore, the cleaning performance gets improved because the value enhances on the top section. The redistribution of pressure drop observed is mainly because the special geometric construction of pleated cartridges compresses the flow on the medium and produce higher pressure drop there. Further studies indicate that the improved cleaning performance was observable under the consideration of the tank pressure reduction and variation of media permeability during each cleaning phase, and the change of pleated cartridge shapes can also improve the cleaning performance when combined with other improvement methods. [ABSTRACT FROM AUTHOR]

The article deals with the questions of mathematical modeling of compressible jet outflow from model nozzle and jet impingiment on flat plate at various values of n. pisoCentralFoam solver which is based on the Kurganov-Tadmor hybrid numerical scheme, PISO algorithm and finite volume method, is used for the solution of this problem. The model, based on unsteady Reynolds equation and K-omega SST turbulence model with boundary functions is used for compressible jet calculation. The problem definition for calculation of jet impingiment on flat plate is given. The simulation domainwas selected as a rectangle. Only a half of the nozzle was considered for simplification. The mixed boundary condition for pressure setting in case of free jet was used on the outlet of simulation domain. The special condition for the pressure with table data, allowed to increase the value of pressure gradually, was used on the inlet of simulation domain. The value of the jet pressure degree was selected as n = 2.5 and n = 5.0. The results of distribution of the velocity magnitude, field pressure, upon symmetry axes were received. The simulations were done with grids 100 000-500 000 cells. The average value of y+ was equal to 270. The calculations were done for the end time Tend = 0.01 s. Comparison of the results of pressure distribution calculation based on nozzle length on different grids with the results of the experiment is carried out. The coincidence to engineering accuracy of 5 % is received.

The unsteady phenomenon abounds in centrifugal compressors and significantly affects the compressor performance. In this paper, unsteady simulations are carried out to investigate the aerodynamic performance of a process-unshrouded centrifugal compressor and the unsteady mechanism in the vaned diffuser. The predicted stage performance and pressure fluctuations at some locations are in good agreement with experimental data. The predicted main pressure fluctuation frequency spectrums at the diffuser inlet and outlet are consistent with the measured results. The results indicate that at the inlet of the diffuser there are two pressure peaks in a passage cycle. The higher pressure peak relates to the impeller wake and the lower peak is connected with the vortex generated at the diffuser’s leading edge. With a decrease in the mass flow coefficient, the vortex core region becomes larger and the lower pressure peak becomes more pronounced. The change in circumferential flow angle at the diffuser inlet is mainly responsible for the unsteadiness in the diffuser flow field, which in turn affects the inlet incidence of the diffuser vane and the vane loading distributions.

The paper handles the subject of the modelling and simulation of the flow inside a centrifugal pump through non-cavitating and cavitating conditions. Operating under cavitation state is so perilous to a pump and can considerably reduce its lifetime service. Hence, to provide highly reliable pumps, it is essential to comprehend the inner flow of pumps. The investigated centrifugal pump comprises five backward curved-bladed impeller running at 900 rpm. The modelling process started with an unsteady numerical analysis under non-cavitating conditions to validate the numerical model and the solver comparing with the available testing data. Due to high Reynolds numbers, turbulence effects have been taken into account by unsteady RANS methods using an SST-SAS turbulence model. The obtained pump performances were numerically compared with the experimental ones, and the outcome shows an acceptable agreement between both. The temporal distribution of the internal flow parameters such as pressure and velocity was then studied. Furthermore, basic investigations of cavitating flow around 3D NACA66-MOD profile using a recently developed and validate cavitation model was established. The verification of the numerical simulation validity was based on comparing calculated and experimental results and presented good agreement. Finally, a 3D simulation of the inception of the cavitating pocket inside the centrifugal pump is performed to analyze the impact of the cavitation in the decrease of the head and efficiency. [ABSTRACT FROM AUTHOR]

To investigate the effects of matching characteristics of tandem cascade on the performance and flow at large angle of attack, the unsteady numerical simulation has been implemented. The influences of different turning angle ratio (TR) and chord length ratio (CR) of two blades and the relative angle of attack of rear blade (Delta) are analyzed. The numerical results indicated that the tandem cascade can obtain overall performance improvement including higher static pressure ratio and lower total pressure loss with the matching parameters in the range of TR=3~5, CR=0.5~1.2, and Delta=-15°~-5°. The separation on the front blade has more prominent impact than that on the rear blade, so the performance improvement of tandem cascade is significantly dependent on the reduction of front-blade separation and loss. Regarding the rear blade, the gap injection effect can periodically control the separation. Temporal and spatial analysis of the flow field shows that the optimal-performance cases generally have much smaller wake loss for both two blades, but the unsteady characteristics of the wake loss is more apparent than that of the poor performance cases. [ABSTRACT FROM AUTHOR]

To compromise the compression efficiency and the starting properties, the inner contraction ratio (ICR) of a general high Mach number inlet is usually designed in the range of dual solution area. When going into an unstarted status, the high Mach inlet needs an assistant method to restart. This work explores a variable geometry method to restart the inlet. The rotating cowl is adopted to a typical Mach 4 cruising inlet, and the unsteady computation method with a dynamic Chimera grid technique is applied to simulate the rotating process of the inlet cowl. The change characteristics of the restarted performance at different rotating angle amplitude of the inlet cowl are investigated systematically. The numerical results reveal that the unstarted status of this typical inlet induced by the effect of high backpressure failed to restart if the inlet cowl rotating angle amplitude is under a small critical value, which is called lower critical angle. The inlet could restart if the cowl rotating angle amplitude is a little larger than the lower critical angle, and the flow may rapidly go to a steady condition after the inlet cowl returns to the design position. However, the performance of the restarted inlet is still worse than the design condition, because of the existence of an stable separation bubble on its shoulder, even if the inlet cowl stops rotating. The separation bubble becomes shrunk with an increasing the cowl rotating angle amplitude. When the inlet cowl rotating angle amplitude reaches a large critical value which is called upper critical angle, the separation bubble disappears, and all the separation is swallowed by the mean flow. Therefore the design performance of the inlet can be recovered, which means that the flow mass capture coefficient, total pressure recovery coefficient, drag and the outlet Mach number go back to the design level. It also shows that within the range of the lower and upper critical angles, the larger the rotating angle amplitude is, the more rapidly the separation bubble reaches stable state. [ABSTRACT FROM AUTHOR]

An unsteady numerical analysis has been conducted to study the strong interaction between impeller blade and volute tongue of a centrifugal pump. The 3-D-URANS equations were solved with the shear stress transport turbulence model for a wide range of flow rates. These unsteady interactions are mostly related to the unsteady radial force due to an imbalance in the pressure field at the impeller periphery. This force represents dynamic load that are one of the most important sources of vibration and hydraulic noise. Based on this phenomenon, this work analyzes and gives a more realistic prediction of the pressure fluctuation and the radial force during steady and unsteady calculation by considering the effect of the change in the pump operating point. Actually, the pressure fluctuations in the impeller and the volute were recorded by mounting nine monitoring points on the impeller and volute casing. The results of the existing analysis has proven that the pressure fluctuation is periodic due to the relative position of impeller blade to volute tongue. The characteristics of the time domain and frequency domain of the pressure pulsation were analyzed under different coupling conditions. Fast Fourier transform was performed to obtain the spectra of pressure pulsation. Besides, the steady and unsteady forces were calculated around the impeller periphery to fully characterize the pump behavior. The obtained pump performance curves were numerically compared with the experimental ones, and the outcome have shown an acceptable agreement between both curves. [ABSTRACT FROM AUTHOR]

The ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine due to advantages of high efficiency and low Specific Fuel Consumption (SFC). One of the characteristics of ultra-high bypass ratio turbofan is the intermediate turbine duct which guides the flow leaving high pressure turbine (HPT) to low pressure turbine (LPT) at a larger diameter, and this kind of design will lead to aggressive intermediate turbine duct (AITD) design concept. Thus, it is important to design the AITD without any severe loss. From the unsteady flow’s point of view, in actual operating conditions, the incoming wake generated by HPT is unsteady which will take influence on boundary layer’s transition within the ITD and LPT. In this paper, the three-dimensional unsteady aerodynamics of an AITD taken from a real engine is studied. The results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX (RANS simulation with transitional model), are critically evaluated against experimental data. After validation of the numerical model, the physical mechanisms inside the flow channel are analyzed, with an aim to quantify the sensitivities of different Reynolds number effect on both the ITD and LPT nozzle. Some general physical mechanisms can be recognized in the unsteady environment. It is recognized that wake characteristics plays a crucial role on the loss within both the ITD and LPT nozzle section, determining both time-averaged and time-resolved characteristics of the flow field. Meanwhile, particular attention needs to be paid to the unsteady effect on the boundary layer of LPT nozzle’s suction side surface. [ABSTRACT FROM AUTHOR]

In this paper, a series of simulations and experiments about hydrogen peroxide throttleable catalyst hybrid rocket motor were conducted during thrust regulation process. Some characteristics of this motor were investigated such as regression rate, pressure in chamber and thrust. The motor used polyethylene (PE) as the solid fuel and 90% hydrogen peroxide (H 2 O 2 ) as the oxidizer. To investigate transient process of this throttleable motor, an unsteady simulation model was developed. The realizable k – ε turbulence model combined with the Eddy-Dissipation combustion model was applied in this paper, and gas–solid coupling model was used to simulate the regression process on the solid fuel surface. The distributions of temperature, pressure and solid fuel regression rate were obtained. A series of tests were conducted to verify the accuracy of the simulation model. From the comparison of the pressure in chamber between the simulation and test, the maximum error is 9%. The numerical model could predict the characteristics of this motor. The simulation results and the experimental data indicate that the chamber pressure and fuel regression rate cannot response to the oxidizer mass flow rate change immediately, it requires a lag time to readjust to new equilibrium. [ABSTRACT FROM AUTHOR]

Unsteady numerical simulations of a high-load transonic turbine stage have been carried out to study the influences of vane trailing edge outer-extending shockwave on rotor blade leading edge film cooling performance. The turbine stage used in this paper is composed of a vane section and a rotor one which are both near the root section of a transonic high-load turbine stage. The Mach number is 0.94 at vane outlet, and the relative Mach number is above 1.10 at rotor outlet. Various positions and oblique angles of film cooling holes were investigated in this research. Results show that the cooling efficiency on the blade surface of rotor near leading edge is significantly affected by vane trailing edge outer-extending shockwave in some cases. In the cases that film holes are close to leading edge, cooling performance suffers more from the sweeping vane trailing edge outer-extending shockwave. In addition, coolant flow ejected from oblique film holes is harder to separate from the blade surface of rotor, and can cover more blade area even under the effects of sweeping vane trailing edge shockwave. As a result, oblique film holes can provide better film cooling performance than vertical film holes do near the leading edge on turbine blade which is swept by shockwaves. [ABSTRACT FROM AUTHOR]

In order to have a further insight into the dynamic build-up process of particle deposits within the high-pressure turbine stator of an aeroengine and also into their effects on aerodynamic performance and heat transfer characteristics of the entire cascade passages, unsteady simulations coupled with a particle-wall interaction model and a dynamic mesh update technology were conducted in this study. The changing tendencies of flow field structures, aerodynamic losses, and heat transfer coefficients were characterized as the deposits on the stator increased with the exposure time. Results reveal that localized deposits with peak-to-valley patterns are generated with the accumulation of particles. The flow path area of the turbine passage is reduced due to the deposits that are mainly concentrated on the pressure side of the stator vane. Energy dissipation is generated as the mainstream gas flows through the fouled stator, which results in the deterioration of aerodynamic performance. Heat transfer presents a different tendency at specific locations on the vane surface with the dynamic deposition. At the early stage of deposition, slight deposits can reduce the thermal load on the vane to a certain extent, while as particles further build up, the heat transfer coefficient of the entire vane surface increases rapidly. [ABSTRACT FROM AUTHOR]

Solar chimney power plant (SCPP) is a promising renewable energy technology that needs policy support and market cultivation at the early stage of its development. An accurate prediction of the levelized cost of electricity (LCOE) can be used as basis for crafting effective support policies. This study presents an unsteady theoretical model that considers hourly meteorological data and soil heat storage in estimating the annual power generation of an SCPP. A cost benefit model is adopted to calculate the LCOE of a 10-MW SCPP in Yinchuan, a representative geographical location in the Northwestern region of China. By considering the cost advantage of China, the concessional loan, as well as the low operation and maintenance cost, the LCOE of the SCPP is estimated to be 0.4178 Yuan/kWh, which can compete with those of wind power and solar PV in China. This work lays a good foundation for the accurate prediction of power generation and provides a reference for the Chinese government in crafting effective support policies for SCPPs. [ABSTRACT FROM AUTHOR]

The flow field investigation around marine propellers is of great importance, due to its applications in vessels identification and hydrodynamic noise prediction. In the present research, the steady and unsteady wake flow field was simulated using the RANS equations with the open-source OpenFOAM software and the simple-Foam and Pimple-DyMFoam solvers. The obtained characteristic chart and near propeller wake flow results were validated against available experimental data, and were shown to be in a very good agreement. The grid study results in the wake region prove that unlike global quantities, the employed wake grid strongly affects the wake parameters. The results obtained from the present research show that employing the RANS models is suitable for the hydrodynamic coefficients calculation and these models predict the results with a low computational cost against the Unsteady RANS approach. On the other hand, an accurate investigation of the flow fluctuations and the vortex flow instabilities can only be accrued performing unsteady simulations with an appropriate refined grid. In this research, the effect of advance coefficient is also investigated on the vortex flow pattern in the wake region. Qualitative comparison of the obtained results and similar available data of the more accurate DES turbulence model shows that the URANS method has great capabilities in wake flow simulation provided that a suitable grid is applied. This method significantly decreases the required cells number and run time while maintaining the results accuracy. [ABSTRACT FROM AUTHOR]

Mixed heat convection of three-dimensional unsteady flow of four different types of fluids in a double lid-driven enclosure is simulated by a two-phase mixture model in this project. The cubic cavity with moving isothermal sidewalls has uniform heat flux on the middle part of the bottom wall, and the other remaining walls forming the enclosure are adiabatic and stationary. The relevant parameters in the present research include Reynolds number Re (5000–30,000), nanoparticle diameter (25 nm–85 nm), and nanoparticle volume fraction (0.00–0.08). In general, remarkable effects on the heat transfer and fluid patterns are observed by using nanofluids in comparison to the conventional fluid. Different types of nanofluids or different diameters of nanoparticles can make pronounced changes in the heat convection ratio. In addition, increasing in either volume fraction of nanoparticles or Reynolds number leads to increasing in the Nusselt number, fluctuation kinetic energy and root mean square velocity of the fluid in the domain. It is also found that both URANS and LES methods have shown good performance in dealing with unsteady flow conducted in this project. However, the comparisons have elucidated clearly the advantages of the LES approach in predicting more detailed heat and flow structures. [ABSTRACT FROM AUTHOR]

Dynamic stall, caused by flow separation, will take place on any profile or other surfaces that are exposed to time-dependentmotion in the flow, such as change in angle of attack, wing flapping respectively or another vertical movement. The study comparerresults of simulations of flow around airfoil FX 63-137.