Influence of Turbulence Models in Transient Simulations of Inducers Under Steady Operation

2019 ◽  
Author(s):  
Björn Gwiasda ◽  
Matthias Mohr ◽  
Dennis Herrmann-Verspagen ◽  
Martin Böhle
Keyword(s):  
Turbulence Model ◽  
Turbulence Models ◽  
Leading Edge ◽  
Geometrical Parameters ◽  
Transient Effects ◽  
Cfd Simulations ◽  
Transient Simulations ◽  
Models Comparison ◽  
Transient Data ◽  
Additional Influence

Abstract A significant uncertainty in full transient 3D-CFD simulations of inducers is the used turbulence model. To investigate the influence of different turbulence models (Spalart-Allmaras, SST, SSG) on the transient effects experiments and simulations are performed for two inducers. In this paper the results of simulations are represented that are performed under noncavitating conditions to exclude the additional influence of the cavitation model in order to gain an isolated understanding for the influence of turbulence models. Comparison of transient data from simulations as well as experiments determines the influence of the turbulence model. For the investigations two different inducers are designed with different leading edges. One inducer with a straight leading edge and one with a back swept leading edge. All other geometrical parameters are kept constant, such as the hub contour which is purely axial.

scholarly journals Assessment of CFD turbulence models for free surface flow simulation and 1-D modelling for water level calculations over a broad-crested weir floodway

Water SA ◽  
2019 ◽  
Vol 45 (3 July) ◽  
Author(s):  
Ahmed M Helmi
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Water Level ◽  
Dimensional Analysis ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Cfd Simulations ◽  
One Dimensional ◽  
The Mean ◽  
The One

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

Investigation of Annular Jet Flows in a Subsonic Air-Air Ejector With Multi-Ring Entraining Diffuser

2015 ◽  
Author(s):  
A. Namet-Allah ◽  
A. M. Birk
Keyword(s):  
Boundary Conditions ◽  
Turbulence Model ◽  
Nozzle Exit ◽  
Turbulence Models ◽  
Domain Size ◽  
Pressure Recovery ◽  
Cfd Simulations ◽  
The Core ◽  
Measured Flow ◽  
Air Ejector

The current paper presents a cold flow simulation study of a low Mach number air-air ejector with a four ring entraining diffuser that is used in a variety of applications including infrared (IR) suppression of exhaust from helicopters and fixed wing aircraft. The main objectives of this investigation were to identify key issues that must be addressed in successful CFD modelling of such devices, and recognize opportunities to improve the performance of these devices. Two-dimensional CFD simulations were carried out using commercial software, Ansys14. Studies of mesh and domain size sensitivity were made to ensure the CFD results were independent of both factors. A turbulence model independence study using k-ε, k-ω and RSM turbulence models was performed to figure out the appropriate turbulence model that produced the best agreement with the experimental data for several of ejector performance criteria. The measured flow properties in the annulus were used as input boundary conditions for the CFD simulations. However, in the comprehensive turbulence model study, the measured flow parameters at the nozzle exit were also applied as inlet boundary conditions for the CFD simulations. The measured flow velocity at the nozzle exit, at one centerline section inside the mixing tube and at the diffuser exit and the system pressure recovery were compared with the CFD predictions. The ejector pumping ratios, back pressure coefficient and diffuser gap velocities were also compared. It was found that the RANS-based CFD predictions were sensitive to the changes in the ejector domain size, mesh refinement and inlet boundary condition locations. With the annulus inlet boundary conditions, the tested turbulence models under predicted the size of the core separation downstream of the system, back pressure, pumping ratio and pressure recovery in the mixing tube and diffuser. However, the ability of the RNG turbulence model to predict the ejector performance parameters was better than that of the other turbulence models at all inlet flow conditions. Nevertheless, applying the inlet boundary conditions at the nozzle exit enhanced the capability of the RANS-based turbulence model particularly in predicting the ejector pumping ratios, pressure recovery and the size of the core separation. Finally, the acceptable agreement between the experimental data and the CFD predictions provides a valid tool to continue improving these devices using CFD techniques.

A New Unsteady-Based Turbulence Model to Predict Shear Layer Rollup and Breakdown

2004 ◽  
Author(s):  
D. Scott Holloway ◽  
James H. Leylek
Keyword(s):  
Shear Layer ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Separated Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Aircraft Carrier ◽  
Flow Through

This paper documents the computational investigation of the unsteady rollup and breakdown of a turbulent separated shear layer. This complex phenomenon plays a key role in many applications, such as separated flow at the leading edge of an airfoil at off-design conditions; flow through the tip clearance of a rotor in a gas turbine; flow over the front of an automobile or aircraft carrier; and flow through turbulated passages that are used to cool turbine blades. Computationally, this problem poses a significant challenge in the use of traditional RANS-based turbulence models for the prediction of unsteady flows. To demonstrate this point, a series of 2-D and 3-D unsteady simulations have been performed using a variety of well-known turbulence models, including the “realizable” k-ε model, a differential Reynolds stress model, and a new model developed by the present authors that contains physics that account for the effects of local unsteadiness on turbulence. All simulations are fully converged and grid independent in the unsteady framework. A proven computational methodology is used that takes care of several important aspects, including high-quality meshes (2.5 million finite volumes for 3-D simulations) and a discretization scheme that will minimize the effects of numerical diffusion. To isolate the shear layer breakdown phenomenon, the well-studied flow over a blunt leading edge (Reynolds number based on plate half-thickness of 26,000) is used for validation. Surprisingly, none of the traditional eddy-viscosity or Reynolds stress models are able to predict an unsteady behavior even with modifications in the near-wall treatment, repeated adaption of the mesh, or by adding small random perturbations to the flow field. The newly developed unsteady-based turbulence model is shown to predict some important features of the shear layer rollup and breakdown.

scholarly journals Influence of Turbulence Model for Wind Turbine Simulation in Low Reynolds Number

2016 ◽  
Vol 2016 ◽  
pp. 1-9
Author(s):  
Masami Suzuki
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Leading Edge ◽  
Wind Tunnel Experiment ◽  
Speed Ratio ◽  
Horizontal Axis Wind Turbine ◽  
Developed Turbulence

In designing a wind turbine, the validation of the mathematical model’s result is normally carried out by comparison with wind tunnel experiment data. However, the Reynolds number of the wind tunnel experiment is low, and the flow does not match fully developed turbulence on the leading edge of a wind turbine blade. Therefore, the transition area from laminar to turbulent flow becomes wide under these conditions, and the separation point is difficult to predict using turbulence models. The prediction precision decreases dramatically when working with tip speed ratios less than the maximum power point. This study carries out a steadiness calculation with turbulence model and an unsteadiness calculation with laminar model for a three-blade horizontal axis wind turbine. The validation of the calculations is performed by comparing with experimental results. The power coefficients calculated without turbulence models are in agreement with the experimental data for a tip speed ratio greater than 5.

Prediction of a Laminar Separation Bubble Over a Controlled-Diffusion Compressor Blade

2000 ◽  
Author(s):  
G. V. Hobson ◽  
S. Weber
Keyword(s):  
Turbulence Model ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Leading Edge ◽  
Equation Model ◽  
Implicit Time ◽  
Controlled Diffusion ◽  
Time Marching ◽  
The One ◽  
Edge Separation

The paper describes the comparison of the prediction of the flow through a cascade of controlled-diffusion compressor blades with two Navier-Stokes solvers. Both codes solved the thin-layer N-S equations, however; one code performed implicit time marching whereas the other performed explicit time marching. Flow predictions were accomplished with the implicit code using the algebraic turbulence model of Baldwin and Lomax and the one-equation model of Spalart and Allmaras, while predictions were made with the explicit code using the two-equation model by Wilcox. Predictions were made of the detailed laser-anemometry measurements of the flow field taken previously in a low-speed cascade wind tunnel. Comparisons were also made with the experimentally measured blade surface pressures and flow visualization of the extent of the laminar leading edge separation bubble. The one-equation turbulence model was combined with an intermittency based transition-length model for comparisons with fully turbulent calculations. Both codes predicted the leading-edge separation bubble satisfactorily when using higher order turbulence models.

Validation of CFD simulations for X-31 wind-tunnel models

2015 ◽  
Vol 119 (1214) ◽  
pp. 479-500 ◽  
Author(s):  
M. Ghoreyshi ◽  
A. D. H. Kim ◽  
A. Jirasek ◽  
A. J. Lofthouse ◽  
R. M. Cummings
Keyword(s):  
Wind Tunnel ◽  
Aerodynamic Force ◽  
Numerical Algorithms ◽  
Turbulence Models ◽  
Leading Edge ◽  
Convergence Acceleration ◽  
Cfd Simulations ◽  
Data Set ◽  
Cfd Models ◽  
Sinusoidal Oscillations

AbstractComputational Fluid Dynamics (CFD) has become an attractive method of choice in the design of many aerospace vehicles because of advances in numerical algorithms and convergence acceleration methods. However, the flow around an advanced fighter aircraft is complicated and usually unsteady due to the presence of vortex-dominated flows. The accuracy and predictability of conventional turbulence models for these applications may be questionable and therefore results obtained from these models must be validated and evaluated on the basis of experimental data from wind tunnels and/or flight tests. This work aims to validate CFD simulations of X-31 wind-tunnel models with and without a belly-mounted sting. The sting setup facilitates forced sinusoidal oscillations in one of three modes of: pitch, yaw, and roll. However, the results show that measured aerodynamic data are altered by the turbulent wake behind the sting, even at small angles of attack. The high angle-of-attack flow around the X-31 is also very complicated and unsteady due to canard and wing vortices. Therefore, validation of CFD models for predicting these complex flows can be a very challenging task. The X-31 wind-tunnel experiments were carried out in the German Dutch low-speed wind tunnel at Braunschweig and include aerodynamic force and moment measurement as well as span-wise pressure distributions at locations of 60% and 70% chord length. This data set is used to validate the Cobalt and Kestrel flow solvers and the results are similar and match quiet well with experiments for small to moderate angles of attack. The main discrepancies between CFD and measurements occur close to the wing tip, where leading-edge flaps are located.

scholarly journals NEW METHODS FOR STABILIZING RANS TURBULENCE MODELS WITH APPLICATION TO LARGE SCALE BREAKING WAVES

2020 ◽  
pp. 19
Author(s):  
Georgios Azorakos ◽  
Bjarke Eltard Larsen ◽  
David R. Fuhrman
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Breaking Waves ◽  
Wide Spread ◽  
Cfd Simulations ◽  
New Methods ◽  
Rans Turbulence Models ◽  
Scale Breaking

Recently, Larsen and Fuhrman (2018) have shown that seemingly all commonly used (both k-omega and k-epsilon variants) two-equation RANS turbulence closure models are unconditionally unstable in the potential flow beneath surface waves, helping to explain the wide-spread over-production of turbulent kinetic energy in CFD simulations, relative to measurements. They devised and tested a new formally stabilized formulation of the widely used k-omega turbulence model, making use of a modified eddy viscosity. In the present work, three new formally-stable k-omega turbulence model formulations are derived and tested in CFD simulations involving the flow and dynamics beneath large-scale plunging breaking waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T2fFRgq3I8E

scholarly journals Heat Transfer on a Film-Cooled Rotating Blade Using a Two-Equation Turbulence Model

1998 ◽  
Vol 4 (3) ◽  
pp. 201-216 ◽  
Author(s):  
Vijay K. Garg
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Leading Edge ◽  
Equation Model ◽  
Tip Clearance ◽  
Suction Surface ◽  
Pressure Surface ◽  
Rotating Blade

A three-dimensional Navier–Stokes code has been used to compare the heat transfer coefficient on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire span. This is the only filmcooled rotating blade over which experimental data is available for comparison. Over 2.278 million grid points are used to compute the flow over the blade including the tip clearance region, using Coakley'sq-ωturbulence model. Results are also compared with those obtained by Garg and Abhari (1997) using the zero-equation Baldwin-Lomax (B-L) model. A reasonably good comparison with the experimental data is obtained on the suction surface for both the turbulence models. At the leading edge, the B-L model yields a better comparison than theq-ωmodel. On the pressure surface, however, the comparison between the experimental data and the prediction from either turbulence model is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present computations. Prediction using the two-equation model is in general poorer than that using the zero-equation model, while the former requires at least 40% more computational resources.

Analysis and Modifications of Turbulence Models for Wind Turbine Wake Simulations in Atmospheric Boundary Layers

2016 ◽  
Author(s):  
Enrico G. A. Antonini ◽  
David A. Romero ◽  
Cristina H. Amon
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Cfd Simulations ◽  
Rans Equations ◽  
Stress Models ◽  
Turbine Wake ◽  
Wind Turbine Wake

Computational Fluid Dynamics (CFD) simulations of wind turbine wakes are strongly influenced by the choice of the turbulence model used to close the Reynolds-averaged Navier-Stokes (RANS) equations. A wrong choice can lead to incorrect predictions of the velocity field characterizing the wind turbine wake, and consequently to an incorrect power estimation for wind turbines operating downstream. This study aims to investigate the influence of different turbulence models on the results of CFD wind turbine simulations. In particular, the k–ε, k–ω, SSTk–ω, and Reynolds stress models are used to close the RANS equations and their influence on the CFD simulations is evaluated from the flow field generated downstream a stand-alone wind turbine. The assessment of the turbulence models was conducted by comparing the CFD results with publicly available experimental measurements of the flow field from the Sexbierum wind farm. Consistent turbulence model constants were proposed for atmospheric boundary layer and wake flows according to previous literature and appropriate experimental observations. Modifications of the derived turbulence model constants were also investigated in order to improve agreement with experimental data. The results showed that the simulations using the k–ε and k–ω turbulence models consistently overestimated the velocity in the wind turbine wakes. On the other hand, the simulations using the SSTk–ω and Reynolds stress models could accurately capture the velocity in the wake of the wind turbine. Results also showed that the predictions from the k–ε and k–ω turbulence models could be improved by using the modified set of turbulence coefficients.

Performance improvement of a high-speed aero-fuel centrifugal pump through active inlet injector

2020 ◽  
pp. 095441002096096
Author(s):  
Jia Li ◽  
Xin Wang ◽  
Wancheng Wang ◽  
Yue Wang
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Turbulence Model ◽  
High Speed ◽  
Flow Direction ◽  
Active Flow Control ◽  
Turbulence Models ◽  
Internal Flow ◽  
Geometrical Parameters ◽  
Centrifugal Pumps

This paper presents a high-speed aero-fuel centrifugal pump with an active inlet injector for an aero-engine aiming at regulating the internal flow field and improving overall hydraulic performance. Unlike most of the existing centrifugal pumps for aero-engines, an injector is designed and integrated with the pump to accomplish the active flow control. Firstly, by employing the energy equation in the pump, reasonable geometrical parameters of the injector are calculated. Then, a validation study is conducted with three known turbulence models, showing that simulations with the RNG κ- ε turbulence model can accurately predict the head and efficiency of the experimental pump. Finally, simulation results with the determined turbulence model are discussed. The results show that the static pressure is uniformly distributed inside the impeller, the volute and the injector. The flow field is significantly ameliorated by improving the pressure inside the suction pipe and controlling the flow direction via the injector. Furthermore, the head and efficiency of the designed pump with an active inlet injector are improved compared to the one without an injector.

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