Wray-Agarwal Model Research Articles

Vortex dynamics characteristics in the tip region based on Wray–Agarwal model

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps.

Evaluation of Various Turbulence Models and Large Eddy Simulation for Stall Prediction in a Centrifugal Pump

Rotational stall is an unstable flow phenomenon that reduces the performance of centrifugal pumps, usually occurring under partial load conditions. It causes instability in the flow resulting in intense vibrations and noise under certain flow conditions. In this study, the one-equation Wray–Agarwal (WA) turbulence model, which was recently developed, is employed to numerically simulate the internal flow field of a centrifugal pump under the deep stall condition. The aim of this study is to examine the prediction accuracy for stall by using the WA turbulence model. The method based on computational fluid dynamics (CFD) has been widely applied for investigation of complex flow patterns in pumps by solving Reynolds-averaged Navier-Stokes (RANS) equations. Particle image velocimetry (PIV) experimental results were compared with simulations predicted using the WA, renormalization group (RNG) k−ε, shear stress transport (SST) k−ω, and realizable k−ε turbulence models and large eddy simulations (LES). The comparisons indicated that the WA turbulence model can accurately predict the flow separation and has a good agreement with the PIV data. The WA model adds a cross-diffusion term and a blending function to the eddy viscosity R equation, so that this model could be expressed as a one-equation k−ω model or one-equation k−ε model as needed by using the switching function. The results show the strong potential of the WA model for accurately computing the stall in rotating fluid machinery. The outcomes of the study are useful in development and optimization of fluid machinery with a low calculation cost and a high accuracy.

Application of Wray–Agarwal Turbulence Model for Numerical Simulation of Gas-Solid Flows in Circulating Fluidized Bed Risers

Abstract In recent decades, increasing attention has been paid on accurate modeling of circulating fluidized bed (CFB) risers to provide valuable guidance to design, optimization, and operation of reactors. Turbulence model plays an important role in the accurate prediction of complex gas-solid flows. Recently developed Wray–Agarwal (WA) model is a one-equation turbulence model with the advantages of high computational efficiency and competitive accuracy with two-equation models. In this paper for the first time, the Eulerian–Eulerian approach coupled with different turbulence models including WA model, standard κ–ɛ model, and shear stress transport (SST) κ–ω model is employed to simulate two-phase flows of gas phase and solid phase in two CFB risers, in order to assess accuracy and efficiency of WA model compared to other well-known two-equation models. Predicted gas-solid flow dynamic characteristics including the gas-solid volume fraction distributions in radial and axial directions, pressure profiles, and solid mass flux distributions are compared with data obtained from an experiment in detail. The results demonstrate that the WA model is very promising for accurate and efficient simulation of gas-solid multiphase flows.

Application of Wray–Agarwal Turbulence Model in Flow Simulation of a Centrifugal Pump With Semispiral Suction Chamber

Abstract The Wray–Agarwal (WA) turbulence model is selected to simulate the internal and external characteristics of a centrifugal pump with semispiral suction chamber; the numerical results are compared with the experimental data and computed results predicted by standard k–ε, renormalization group (RNG) k–ε, and shear stress transport (SST) k–ω turbulence models. The results show that the WA model could be effectively used to compute the energy performance of centrifugal pump under full range of operating conditions and gives higher accuracy than other models. Overall, the WA model shows closer similarity to the experimental data and gives more uniform flow field in the impeller region compared to that predicted by other models. In prediction of internal flow fields of the pump, overall the WA model is more accurate and efficient being a one-equation model. The control of undamped eddy viscosity variable R (= k/ω) in WA model does not allow the overestimation of turbulent kinetic energy and turbulent eddy frequency obtained with other models, which leads to its advantage in accurate prediction of both internal and external flow characteristics of centrifugal pump.

Computation of gas-liquid flow in a square bubble column with Wray-Agarwal one-equation turbulence model

The newly proposed one-equation Wray-Agarwal (WA) turbulence model coupled with Euler-Euler (E-E) approach was used to simulate the gas-liquid flow in a square bubble column, which further validated the accuracy and expanded the application of the WA model comparing to a preliminary study (Ouyang et al., 2019). All simulation results of the WA model were compared with two widely used turbulence models of standard k-ε and SST k-ω and literature data. The numerical results of the time-averaged axial liquid and gas velocity were validated with experimental data, and it was found that the WA model showed overall the best agreement. Profiles of turbulent kinetic energy, turbulent dissipation rate, turbulent viscosity and gas holdup were investigated at three different heights. Results for the first time validate the WA model based on the turbulent characteristic values of gas-liquid flow in the bubble column, which shows its promising prospective in multiphase flow simulation.

Evaluation of various turbulence models for numerical simulation of a multiphase system in a rotating packed bed

Numerical simulations of a multiphase system (synthesis of butyl rubber) in a rotating packed bed (RPB) are reported in this paper. Several turbulence models, namely the Standard k-ε, Realizable k-ε, SST k-ω, RSM, and the recently developed one-equation Wray–Agarwal (WA) turbulence model are used in conjunction with the Reynolds-Averaged Navier-Stokes equations. WA model has been shown to be quite accurate and efficient in a large number of benchmark (50+) wall bounded and free shear flows. In this paper for the first time, WA model coupled with Eulerian multiphase model is successfully implemented to simulate the complex multiphase system RPB. Employing the experimental data available in the literature, numerical results are validated based on the liquid holdup in the RPB and the average molecular weight (Mn) of the butyl rubber. Flow characteristic and polymerization process in the RPB are obtained. The WA model results are compared with those obtained with the Standard k-ε, Realizable k-ε, SST k-ω and RSM models.

Computation of Flow in S Ducts with Wray–Agarwal One-Equation Turbulence Model

This paper focuses on the validation and application of a new one-equation eddy viscosity model derived from closure (the Wray–Agarwal model) for three-dimensional flows in serpentine diffusers (S ducts). The S-duct geometry produces streamline curvature and an adverse pressure gradient, resulting in flow separation. Two S-duct geometries are employed in this investigation: one was used in an experimental study conducted at NASA John H. Glenn Research Center in the early 1990s, and the other used in an experimental study conducted at ONERA–The French Aerospace Lab in 2006 and considered for computational fluid dynamics technology validation during the AIAA Propulsion Aerodynamics Workshops in 2012 and 2014. The computational fluid dynamics flow solver ANSYS Fluent is used for flow calculations. Results from the new “Wray–Agarwal” one-equation turbulence model, the widely used Spalart–Allmaras, and the shear-stress-transport models are compared to the available experimental data. Results obtained with the new Wray–Agarwal turbulence model are very promising. It is shown that this new model matches the experimental data better when compared to the Spalart–Allmaras and shear-stress-transport models.