Thermal Mixing Length Determination by RANS Models in T-Junction

2010 ◽  
Author(s):  
M. Aounallah ◽  
M. Belkadi ◽  
L. Adjlout ◽  
O. Imine
Keyword(s):  
Turbulent Mixing ◽  
Thermal Field ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Numerical Results ◽  
Test Case ◽  
Thermal Mixing ◽  
Rans Turbulence Models ◽  
Rans Models ◽  
Length Determination

In the present study, a numerical simulation is carried out in order to optimize the length of the mixing part of a T-junction to obtain a homogenous temperature distribution at the outlet. Different RANS turbulence models are tested: the Realizable k-ε the k-ω standard and the k-ω SST. The behavior of turbulent mixing flow in the mixing part of the pipe has helped in understanding the causes of discrepancy between the models used. The test case analysed in this paper is an unsteady state three-dimensional turbulent flow. The numerical results obtained show that there is a difference in the prediction of the thermal field when different models are used. The results obtained for both k-ω standard and SST models are closer compared with those given by the Realizable k-ε model. The numerical results show that a distance of x/L = 0.625 from the branch is enough to supply devices with a constant temperature.

Synthesis of a CFD Benchmark for the Thermal Mixing in a Sharp Corner T-Junction With a Wall

2018 ◽  
Author(s):  
Afaque Shams ◽  
Nicolas Edh ◽  
Kristian Angele
Keyword(s):  
Thermal Field ◽  
Turbulence Models ◽  
Temperature Fluctuations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Sharp Corner ◽  
Cfd Validation ◽  
Thermal Mixing ◽  
Eddy Simulation ◽  
Rans Models

This article reports a CFD-benchmark with the purpose of validating different turbulence modelling approaches for the transient heat transfer due to mixing of hot and cold flow in a T-junction including the wall. This validation exercise has been carried out within the MOTHER project. In the framework of the project, new experiments were performed with a novel measurement sensor allowing the measurements of the fluctuating wall temperature inside the solid pipe wall. The tests were performed for two different Reynolds numbers (Re) 40000 and 60000 and for two different T-junction geometries; a sharp corner and a round corner. The present article reports the synthesis of the CFD validation for a sharp corner T-junction for Re = 40 000. The CFD validation study has been performed using four different CFD softwares, namely STAR-CCM+, Code_Saturne, LESOCC2 and Fluent. In addition, five different turbulence models i.e. wall-function Large Eddy Simulation (LES), Deatched Eddy Simulation (DES), Partially Resolved Numerical Simulation (PRNS), Unsteady Reynolds Averaged Navier-Stokes URANS and RANS were used to perform the CFD computations. The validation exercise has shown that LES gives the best agreement with the experimental data followed by hybrid (LES/RANS), URANS and RANS models, respectively. The velocity and the thermal fields in the fluid region are correctly predicted by the proper use of the LES modelling, whereas, the accurate prediction of the thermal field in the solid requires very long sampling time in order to achieve a statistically converged solution, which of course requires an enormous computational power. Therefore, the statistical convergence of the thermal field in the solid has been found to be a bottleneck in order to accurately predict the temperature fluctuations in the wall. However, measuring the small amplitude temperature fluctuations is also associated with an uncertainty so the disagreement between CFD and measurements (of the order of 10 %) can also be attributed, in part, to uncertainties in the measurements.

scholarly journals A Combined Experimental and Numerical Investigation of the Flow and Heat Transfer Inside a Turbine Vane Cooled by Jet Impingement

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Emmanuel Laroche ◽  
Matthieu Fenot ◽  
Eva Dorignac ◽  
Jean-Jacques Vuillerme ◽  
Laurent Emmanuel Brizzi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Numerical Results ◽  
Point Of View ◽  
Navier Stokes ◽  
Recirculation Flow ◽  
Rans Models ◽  
Unsteady Effects

The present study aims at characterizing the flow field and heat transfer for a schematic but realistic vane cooling scheme. Experimentally, both velocity and heat transfer measurements are conducted to provide a detailed database of the investigated configuration. From a numerical point of view, the configuration is investigated using isotropic and anisotropic Reynolds-averaged Navier–Stokes (RANS) turbulence models. A hybrid RANS/large eddy simulation (LES) technique is also considered to evaluate potential unsteady effects. Both experimental and numerical results show a very complex three-dimensional (3D) flow. Air is not evenly distributed between different injections, mainly because of a large recirculation flow. Due to the strong flow deviation at the hole inlet, the velocity distribution and the turbulence characteristics at the hole exit are far from fully developed profiles. The comparison between particle image velocimetry (PIV) measurements and numerical results shows a reasonable agreement. However, coming to heat transfer, all RANS models exhibit a major overestimation compared to IR thermography measurements. The Billard–Laurence model does not bring any improvement compared to a classical k–ω shear stress transport (SST) model. The hybrid RANS/LES simulation provides the best heat transfer estimation, exhibiting potential unsteady effects ignored by RANS models. Those conclusions are different from the ones usually obtained for a single fully developed impinging jet.

scholarly journals Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Olivier Petit ◽  
Håkan Nilsson
Keyword(s):  
Centrifugal Pump ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Centrifugal Impeller ◽  
Test Case ◽  
Vaned Diffuser ◽  
Pump Test ◽  
Steady Simulation ◽  
Turbulent Models ◽  
Cfd Analyses

Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.

scholarly journals Numerical Investigation of Boundary Layers in Wet Steam Nozzles

2016 ◽  
Author(s):  
Jörg Starzmann ◽  
Fiona R. Hughes ◽  
Alexander J. White ◽  
Marius Grübel ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Side Wall ◽  
Turbulence Models ◽  
Test Case ◽  
Wet Steam ◽  
Compression Waves ◽  
Wall Boundary Layer ◽  
Two Dimensional Flow

Condensing nozzle flows have been used extensively to validate wet steam models. Many test cases are available in the literature and in the past a range of numerical studies have dealt with this challenging task. It is usually assumed that the nozzles provide a one- or two-dimensional flow with a fully turbulent boundary layer. The present paper reviews these assumptions and investigates numerically the influence of boundary layers on dry and wet steam nozzle expansions. For the narrow nozzle of Moses and Stein it is shown that the pressure distribution is significantly affected by the additional blockage due to the side wall boundary layer. Comparison of laminar and turbulent flow predictions for this nozzles suggests that laminar-turbulent transition only occurs after the throat. Other examples are the Binnie nozzle and the Moore nozzles for which it is known that sudden changes in wall curvature produce expansion and compression waves that interact with the boundary layers. The differences between two- and three-dimensional calculations for these cases and the influence of laminar and turbulent boundary layers are discussed. The present results reveal that boundary layer effects can have a considerable impact on the mean nozzle flow and thus on the validation process of condensation models. In order to verify the accuracy of turbulence modelling a test case that is not widely known internationally is included within the present study. This experimental work is remarkable because it includes boundary layer data as well as the usual pressure measurements along the nozzle centreline. Predicted and measured boundary layer profiles are compared and the effect of different turbulence models is discussed. Most of the numerical results are obtained with the in-house wet steam RANS-solver, Steamblock, but for the purpose of comparison the commercial program ANSYS CFX is also used, providing a wider range of standard RANS-based turbulence models.

Using the DLR-F6 Aircraft Model for the Evaluation of the Academic CFD Code “Galatea”

2014 ◽  
Author(s):  
Georgios N. Lygidakis ◽  
Ioannis K. Nikolos
Keyword(s):  
Large Fraction ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Fluid Flows ◽  
Wind Tunnels ◽  
Navier Stokes ◽  
Test Case ◽  
Tetrahedral Elements ◽  
Computational Performance ◽  
Volume Method

Nowadays, the research in the aerospace scientific field relies strongly on CFD (Computational Fluid Dynamics) algorithms, avoiding (initially at least) a large fraction of the extremely time and money consuming experiments in wind tunnels. In this paper such a recently developed academic CFD code, named Galatea, is presented in brief and validated against a benchmark test case. The prediction of compressible fluid flows is succeeded by the relaxation of the Reynolds Averaged Navier-Stokes (RANS) equations, along with appropriate turbulence models (k-ε, k-ω and SST), employed on three-dimensional unstructured hybrid grids, composed of prismatic, pyramidical and tetrahedral elements. For the discretization of the computational field a node-centered finite-volume method is implemented, while for improved computational performance Galatea incorporates an agglomeration multigrid methodology and a suitable parallelization strategy. The proposed algorithm is evaluated against the Wing-Body (WB) and the Wing-Body-Nacelles-Pylons (WBNP) DLR-F6 aircraft configurations, demonstrating its capability for a good performance in terms of accuracy and geometric flexibility.

How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?

2021 ◽  
Author(s):  
Mehran Masoumifar ◽  
Suyash Verma ◽  
Arman Hemmati
Keyword(s):  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Flow Response ◽  
High Reynolds Numbers ◽  
Flow Features ◽  
Rans Models ◽  
Response And Recovery ◽  
High Reynolds

Abstract This study evaluates how Reynolds-Averaged-Navier-Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. Capturing such flow features using turbulence models is still challenging at high Reynolds numbers. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (10000-158000). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relations. The good agreement between our computationally predicted data using Standard k-epsilon model and those of experiments indicated that this model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.

Influence of Rotation on Dynamic Stall

2013 ◽  
Vol 58 (3) ◽  
pp. 1-9 ◽  
Author(s):  
A. D. Gardner ◽  
K. Richter
Keyword(s):  
Three Dimensional ◽  
Time History ◽  
Turbulence Models ◽  
Dynamic Stall ◽  
Test Case ◽  
Test Cases ◽  
Pitching Moment ◽  
Pitching Motion ◽  
Rotating Blade ◽  
Wind Tunnel Data

A computational investigation of the effect of rotation on two-dimensional (2D) deep dynamic stall has been undertaken, showing that the effect of rotation is to reduce the severity of the pitching moment peak and cause earlier reattachment of the flow. A generic single blade rotor geometry was investigated, which had a pitching oscillation around the quarter-chord axis while in hover, causing angle-driven dynamic stall. The results at the midpoint of the blade have the same Mach number (0.31), Reynolds number (1.15 × 106), and pitching motion (α = 13° ± 7°) as a dynamic stall test case for which significant experimental wind tunnel data and 2D computations exist. The rotating blade is compared with 2D computations and computations using the same blade without rotation at Mach 0.31 and with the same pitching motion. All test cases involve geometries propagating into undisturbed flow with no downwash. The three-dimensional (3D) grid computed without rotation had lower lift at the reference section than for a 2D computation with the same geometric angle of attack time history, and the lift overshoot classically observed for Spalart–Allmaras turbulence models during 2D dynamic stall was significantly reduced in the 3D case. Rotation reduced the strength of the dynamic stall vortex, which reduced the accompanying pitching moment peak by 25%.

Evaluation of RANS Models in Predicting Low Reynolds, Free, Turbulent Round Jet

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Shahriar Ghahremanian ◽  
Bahram Moshfegh
Keyword(s):  
Numerical Simulation ◽  
Boundary Conditions ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Diffusion Term ◽  
Turbulent Region ◽  
Round Jet ◽  
Rans Models ◽  
Low Reynolds

In order to study the flow behavior of multiple jets, numerical prediction of the three-dimensional domain of round jets from the nozzle edge up to the turbulent region is essential. The previous numerical studies on the round jet are limited to either two-dimensional investigation with Reynolds-averaged Navier–Stokes (RANS) models or three-dimensional prediction with higher turbulence models such as large eddy simulation (LES) or direct numerical simulation (DNS). The present study tries to evaluate different RANS turbulence models in the three-dimensional simulation of the whole domain of an isothermal, low Re (Re = 2125, 3461, and 4555), free, turbulent round jet. For this evaluation the simulation results from two two-equation (low Re k-ɛ and low Re shear stress transport (SST) k-ω), a transition three-equation (k-kl-ω), and a transition four-equation (SST) eddy-viscosity turbulence models are compared with hot-wire anemometry measurements. Due to the importance of providing correct inlet boundary conditions, the inlet velocity profile, the turbulent kinetic energy (k), and its specific dissipation rate (ω) at the nozzle exit have been employed from an earlier verified numerical simulation. Two-equation RANS models with low Reynolds correction can predict the whole domain (initial, transition, and fully developed regions) of the round jet with prescribed inlet boundary conditions. The transition models could only reach to a good agreement with the measured mean axial velocities and its rms in the initial region. It worth mentioning that the round jet anomaly is still present in the turbulent region of the round jet predicted by the low Re k-ɛ. By comparing the k and the ω predicted by different turbulence models, the blending functions in the cross-diffusion term is found one of the reasons behind the more consistent prediction by the low Re SST k-ω.

Simulation and Validation of Mach Number Effects on Secondary Flow in a Transonic Turbine Cascade Using a Multigrid, k–ε Solver

1998 ◽  
Vol 120 (2) ◽  
pp. 285-297 ◽  
Author(s):  
M. Koiro ◽  
B. Lakshminarayana
Keyword(s):  
Secondary Flow ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Test Case ◽  
Turbine Cascade ◽  
Efficient Manner ◽  
Wall Boundary Layer ◽  
Transonic Turbine ◽  
Mach Numbers

An existing three-dimensional Navier–Stokes flow solver with an explicit Runge–Kutta algorithm and a low-Reynolds-number k–ε turbulence model has been modified in order to simulate turbomachinery flows in a more efficient manner. The solver has been made to converge more rapidly through use of the multigrid technique. Stability problems associated with the use of multigrid in conjunction with two-equation turbulence models are addressed and techniques to alleviate instability are investigated. Validation for the new code was performed with a transonic turbine cascade tested by Perdichizzi. In the fully three-dimensional turbulent cascade, real convergence (i.e., CPU time) was improved nearly two times the original code. Robustness was enhanced with the full multigrid initialization procedure. The same test case was then used to perform a series of simulations that investigated the effect of different exit Mach numbers on secondary flow features. This permitted an in-depth study into the mechanisms of secondary flow formation and secondary losses at high Mach numbers. In this cascade, it was found that secondary losses and secondary flow deviation, which are fairly constant in incompressible flows with similar geometries, underwent a large reduction in the compressible flow range. The structure of the trailing edge shock system and the reduced end wall boundary layer at supersonic exit conditions were shown to be very significant in reducing the amount of secondary flow and losses.

scholarly journals Simulation and Validation of Mach Number Effects on Secondary Flow in a Transonic Turbine Using a Multigrid, k-ε Solver

1996 ◽  
Author(s):  
M. Koiro ◽  
B. Lakshminarayana
Keyword(s):  
Secondary Flow ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Efficient Manner ◽  
Transonic Turbine ◽  
Mach Numbers ◽  
High Mach

An existing three dimensional Navier-Stokes flow solver with an explicit Runge-Kutta algorithm and a low Reynolds number k-ε turbulence model has been modified in order to simulate turbomachinery flows in a more efficient manner. The solver has been made to converge more rapidly through use of the mutligrid technique. Stability problems associated with use of multigrid in conjunction with two equation turbulence models are addressed and techniques to alleviate instability are investigated. Validation for the new code was performed with a transonic turbine cascade tested by Perdichizzi. In the fully three dimensional turbulent cascade, real convergence (i.e. CPU time) was improved nearly two times the original code. Robustness was enhanced with the full multigrid initialization procedure. The same test case was then used to perform a series of simulations that investigated the effect of different exit Mach numbers on secondary flow features. This permitted an in depth study into the mechanisms of secondary flow formation and secondary losses at high Mach numbers. In this cascade, it was found that secondary losses and secondary flow deviation, which are fairly constant in incompressible flows with similar geometries, underwent a large reduction in the compressible flow range. The structure of the trailing edge shock system and the reduced endwall boundary layer at supersonic exit conditions were shown to be very significant in reducing the amount of secondary flow and losses.

Sign in / Sign up

Export Citation Format

Share Document