Measurement of a Recirculating, Two-Dimensional, Turbulent Flow and Comparison to Turbulence Model Predictions. I: Steady State Case

1983 ◽  
Vol 105 (4) ◽  
pp. 439-446 ◽  
Author(s):  
D. R. Boyle ◽  
M. W. Golay
Keyword(s):  
Steady State ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Scale Model ◽  
Test Facility ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Flow Area ◽  
Flow Measurements

Turbulent flow measurements have been performed in a two-dimensional flow cell which is a 1/15-scale model of the Fast Flux Test Facility nuclear reactor outlet plenum. In a steady water flow, maps of the mean velocity field, turbulence kinetic energy, and Reynolds stress have been obtained using a laser doppler anemometer. The measurements are compared to numerical simulations using both the K–ε and K–σ two-equation turbulence models. A relationship between K–σ and K–ε turbulence models is derived, and the two models are found to be nearly equivalent. The steady-state mean velocity data are predicted well through-out most of the test cell. Calculated spatial distributions of the scalar turbulence quantities are qualitatively similar for both models; however, the predicted distributions do not match the data over major portions of the flow area. The K–σ model provides better estimates of the turbulence quantity magnitudes. The predicted results are highly sensitive to small changes in the turbulence model constants and depend heavily on the levels of inlet turbulence. However, important differences between prediction and measurement cannot be significantly reduced by simple changes to the model’s constants.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Evaluation of Different Turbulence Models Applied in Turbopump’s Hydraulic Turbine

2021 ◽  
Author(s):  
Daniel Ferreira Corrêa Barbosa ◽  
Daniel da Silva Tonon ◽  
Luiz Henrique Lindquist Whitacker ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti
Keyword(s):  
Boundary Conditions ◽  
Turbulence Model ◽  
Rotor Blade ◽  
Space Shuttle ◽  
Turbulence Models ◽  
Tip Clearance ◽  
Test Facility ◽  
Speed Ratio ◽  
Computational Domain ◽  
Axial Turbine

Abstract The aim of this work is an evaluation of different turbulence models applied in Computational Fluid Dynamics (CFD) techniques in the turbomachinery area, in this case, in an axial turbine stage used in turbopump (TP) application. The tip clearance region was considered in this study because it has a high influence in turbomachinery performance. In this region, due to its geometry and the relative movement between the rotor row and casing, there are losses associated with vortices and secondary flow making the flowfield even more turbulent and complex. Moreover, the flow that leaks in the tip region does not participate in the energy transfer between the fluid and rotor blades, degradating the machine efficiency and performance. In this work, the usual flat tip rotor blade geometry was considered. The modeling of turbulent flow based on Reynolds Averaged Navier-Stokes (RANS) equations predicts the variation of turbine operational characteristics that is sufficient for the present turbomachine and flow analysis. Therefore, the appropriate choice of the turbulence model for the study of a given flow is essential to obtain adequate results using numerical approximations. This comparison become important due to the fact that there is no general turbulence model for all engineering applications that has fluid and flow. The turbomachine considered in the present work, is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME), considering the 3.0% tip clearance configuration relative to rotor blade height. The turbulence models evaluated in this work were the SST (Shear Stress Transport), the k-ε Standard and the k-ε RNG. The computational domain was discretized in several control volumes based on unstructured mesh. All the simulations were performed using the commercial software developed by ANSYS, CFX v15.0 (ANSYS). All numerical settings and how the boundary conditions were imposed at different surfaces are explained in the work. The boundary conditions settings follow the same rule used in the test facility and needs some attention during the simulations to vary the Blade-Jet-Speed ratio parameter adequately. The results from numerical simulations, were synthesized and compared with the experimental data published by National Aeronautics and Space Administration (NASA), in which the turbine efficiency and its jet velocity parameter are analyzed for each turbulence model result. The work fluid considered in this work was water, the same fluid used in the NASA test facility.

Assessment of Different Turbulence Models in Helically Coiled Pipes Through Comparison With Experimental Data

2012 ◽  
Author(s):  
Marco Colombo ◽  
Antonio Cammi ◽  
Marco E. Ricotti
Keyword(s):  
Turbulent Flow ◽  
Great Influence ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Test Facility ◽  
Wall Functions ◽  
Pressure Drops ◽  
Fully Developed Turbulent Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Helical Geometry

This paper deals with a comprehensive study of fully developed single-phase turbulent flow and pressure drops in helically coiled channels. To the aim, experimental pressure drops were measured in an experimental campaign conducted at SIET labs, in Piacenza, Italy, in a test facility simulating the Steam Generator (SG) of a Generation III+ integral reactor. Very good agreement is found between data and some of the most common correlations available in literature. Also more data available in literature are considered for comparison. Experimental results are used to assess the results of Computational Fluid Dynamics (CFD) simulations. By means of the commercial CFD package FLUENT, different turbulence models are tested, in particular the Standard, RNG and realizable k-ε models, Shear Stress Transport (SST) k-ω model and second order Reynolds Stress Model (RSM). Moreover, particular attention is placed on the different types of wall functions utilized through the simulations, since they seem to have a great influence on the calculated results. The results aim to be a contribution to the assessment of the capability of turbulence models to simulate fully developed turbulent flow and pressure drops in helical geometry.

scholarly journals Condensates in thin-layer turbulence

2019 ◽  
Vol 864 ◽  
pp. 490-518 ◽  
Author(s):  
Adrian van Kan ◽  
Alexandros Alexakis
Keyword(s):  
Steady State ◽  
Layer Thickness ◽  
Turbulent Flows ◽  
Mean Field ◽  
Direct Numerical Simulations ◽  
Thin Layers ◽  
Scale Model ◽  
Two Dimensional ◽  
Critical Height ◽  
Basic Features

We examine the steady state of turbulent flows in thin layers using direct numerical simulations. It is shown that when the layer thickness is smaller than a critical height, an inverse cascade arises which leads to the formation of a steady state condensate where most of the energy is concentrated in the largest scale of the system. For layers of thickness smaller than a second critical height, the flow at steady state becomes exactly two-dimensional. The amplitude of the condensate is studied as a function of layer thickness and Reynolds number. Bi-stability and intermittent bursts are found close to the two critical points. The results are interpreted based on a mean-field three-scale model that reproduces some of the basic features of the numerical results.

Computational Fluid Dynamics Study for Improvement of Prediction of Various Thermally Stratified Turbulent Boundary Layers

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Hirofumi Hattori ◽  
Tomoya Houra ◽  
Amane Kono ◽  
Shota Yoshikawa
Keyword(s):  
Boundary Layers ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Eddy Diffusivity ◽  
Turbulent Boundary Layers ◽  
Heat Fluxes ◽  
Shear Stresses ◽  
Turbulent Heat ◽  
Two Dimensional ◽  
Turbulent Statistics

The objectives of this study are to reconstruct a turbulence model of both the large Eddy simulation (LES) and the Reynolds-averaged Navier–Stokes simulation (RANS) which can predict wind synopsis in various thermally stratified turbulent boundary layers over any obstacles. Hence, the direct numerical simulation (DNS) of various thermally stratified turbulent boundary layers with/without forward-step, two-dimensional block, or two-dimensional hill is carried out in order to obtain detailed turbulent statistics for the construction of a database for the evaluation of a turbulence model. Also, DNS clearly reveals the characteristics of various thermally stratified turbulent boundary layers with/without forward-step, two-dimensional block, or two-dimensional hill. The turbulence models employed in LES and RANS are evaluated using the DNS database we obtained. In the LES, an evaluated turbulence model gives proper predictions, but the quantitative agreement of Reynolds shear stress with DNS results is difficult to predict. On the other hand, the nonlinear eddy diffusivity turbulence models for Reynolds stress and turbulent heat flux are also evaluated using DNS results of various thermally stratified turbulent boundary layers over a forward-step in which the turbulence models are evaluated using an a priori method. Although the evaluated models do not make it easy to properly predict the Reynolds shear stresses in all cases, the turbulent heat fluxes can be qualitatively predicted by the nonlinear eddy diffusivity for a heat turbulence model. Therefore, the turbulence models of LES and RANS should be improved in order to adequately predict various thermally stratified turbulent boundary layers over an obstacle.

Experiments and Simulations on the Steady-State and Transient Behavior of Gas/Liquid Interfaces in Impulse Pipes for Hydrostatic Level Measurements

2012 ◽  
Author(s):  
Stephan Schulz ◽  
Rainer Hampel
Keyword(s):  
Steady State ◽  
Transient Behavior ◽  
Scale Model ◽  
Test Facility ◽  
Reference Level ◽  
Liquid Interfaces ◽  
Phase Boundaries ◽  
Liquid Mass ◽  
Hydrostatic Level ◽  
The Impact

For Boiling Water Reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and therefore to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “Zero Chamber Level Vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bar will be investigated by applying x-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

Transient Lubricating Films With Inertia—Turbulent Flow

1984 ◽  
Vol 106 (1) ◽  
pp. 134-139 ◽  
Author(s):  
H. G. Elrod ◽  
I. Anwar ◽  
R. Colsher
Keyword(s):  
Steady State ◽  
Turbulent Flow ◽  
Stream Function ◽  
Velocity Gradient ◽  
Eddy Viscosity ◽  
Mean Velocity ◽  
Steady State Operation ◽  
Pressure Development ◽  
Transient And Steady State

This paper presents some new equations for the treatment of turbulent lubricating films when the effects of inertia cannot be neglected. The eddy-viscosity concept is used to represent the turbulent stresses in terms of mean-velocity gradient. Transient and steady-state operation are both considered by means of a generalized stream-function-pressure development.

Turbulence Measurements Downstream of a Turbine Cascade at Different Incidence Angles and Pitch-Chord Ratios

1993 ◽  
Author(s):  
Vincenzo Dossena ◽  
Antonio Perdichizzi ◽  
Marina Ubaldi ◽  
Pietro Zunino
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Turbulent Flow Structure

An experimental investigation on a linear turbine cascade has been carried out to study the effects induced by incidence angle and pitch-chord ratio variations on the three-dimensional turbulent flow downstream of the cascade. Previous mean flow measurements have shown how these parameters influence the energy losses and the secondary velocity field. Now detailed hot wire measurements have been performed on a plane located at 22 per cent of an axial chord downstream of the trailing edge, in order to determine the distribution of all the six Reynolds stress tensor components, for three incidence conditions (i = −30, 0, +30 deg) and for three pitch-chord ratios (s/c = 0.58, 0.72, 0.87). Significant changes of the turbulent flow structure, interesting magnitude and distribution of the Reynolds stress components, have been observed for all the considered test conditions. The analysis of the results shows the correlation between the mean flow features and the turbulent quantities and the relationship between the energy loss production and the blade loading variation. The presented data are also suitable for assessing the behaviour of turbulence models in complex 3D flows, on design and off-design conditions.

CFD Analysis for the Turbulent Flow Distribution in a Fuel Assembly with the Split-Type Mixing Vanes by Using the Advanced Scale-Resolving Turbulence Models

2015 ◽  
Vol 752-753 ◽  
pp. 902-907 ◽  
Author(s):  
Gong Hee Lee ◽  
Ae Ju Cheong
Keyword(s):  
Turbulent Flow ◽  
Fuel Assembly ◽  
Turbulence Models ◽  
Measured Data ◽  
Test Facility ◽  
Detached Eddy Simulation ◽  
Axial Velocity Component ◽  
Pressurized Water ◽  
Ansys Cfx ◽  
Significant Difference

In general, the turbulent flow inside PWR (Pressurized Water Reactor) fuel assembly depends on the mixing vane configuration and the pattern of the mixing vane arrangement on the strap of the spacer grid. In this study, in order to examine the turbulent flow structure inside fuel assembly with the split-type mixing vanes, simulations were conducted with the commercial CFD (Computational Fluid Dynamics) software, ANSYS CFX R.14. Two different types of turbulence models, i.e. SAS (Scale-Adaptive Simulation)-SST (Shear Stress Transport) and DES (Detached Eddy Simulation), were used. The predicted results were compared with the measured data from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. Although there were locally differences between the prediction and the measurement, ANSYS CFX R.14 predicted the time averaged velocity field in the reliable level. The predicted horizontal and vertical velocity components were more in agreement with the measured data than the axial velocity component. There was no significant difference in the prediction accuracy of both turbulence models.

scholarly journals The Development of the Mean Flow and Turbulence Structure in an Annular S-Shaped Duct

1994 ◽  
Author(s):  
K. M. Britchford ◽  
J. F. Carrotte ◽  
S. J. Stevens ◽  
J. J. McGuirk
Keyword(s):  
Reynolds Stress ◽  
Laser Doppler Anemometry ◽  
Reynolds Shear Stress ◽  
Turbulence Models ◽  
Test Facility ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Mean Velocity ◽  
Curvature Effects ◽  
The Mean

This paper describes an investigation of the mean and fluctuating flow field within an annular S-shaped duct which is representative of that used to connect the compressor spools of aircraft gas turbine engines. Data was obtained from a fully annular test facility using a 3-component Laser Doppler Anemometry (LDA) system. The measurements indicate that development of the flow within the duct is complex and significantly influenced by the combined effects of streamwise pressure gradients and flow curvature. In addition CFD predictions of the flow, using both the k-ε and Reynolds stress transport equation turbulence models, are compared with the experimental data. Whereas curvature effects are not described properly by the k-ε model, such effects are captured more accurately by the Reynolds stress model leading to a better prediction of the Reynolds shear stress distribution. This, in turn, leads to a more accurate prediction of the mean velocity profiles, as reflected by the boundary layer shape parameters, particularly in the critical regions of the duct where flow separation is most likely to occur.

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