Temperature Corrected Turbulence Model for High Temperature Jet Flow

2004 ◽  
Vol 126 (5) ◽  
pp. 844-850 ◽  
Author(s):  
Khaled S. Abdol-Hamid ◽  
S. Paul Pao ◽  
Steven J. Massey ◽  
Alaa Elmiligui
Keyword(s):  
High Temperature ◽  
Turbulence Model ◽  
Room Temperature ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Supersonic Jet ◽  
Turbulence Models ◽  
Jet Flows ◽  
Viscosity Term ◽  
Mixing Layer Flows

It is well known that the two-equation turbulence models under-predict mixing in the shear layer for high temperature jet flows. These turbulence models were developed and calibrated for room temperature, low Mach number, and plane mixing layer flows. In the present study, four existing modifications to the two-equation turbulence model are implemented in PAB3D and their effect is assessed for high temperature jet flows. In addition, a new temperature gradient correction to the eddy viscosity term is tested and calibrated. The new model was found to be in the best agreement with experimental data for subsonic and supersonic jet flows at both low and high temperatures.

scholarly journals Numerical investigation of algebraic oceanic turbulent mixing-layer models

2013 ◽  
Vol 20 (6) ◽  
pp. 945-954 ◽  
Author(s):  
T. Chacón-Rebollo ◽  
M. Gómez-Mármol ◽  
S. Rubino
Keyword(s):  
Turbulent Mixing ◽  
Finite Time ◽  
Eddy Viscosity ◽  
Initial Conditions ◽  
Mixing Layer ◽  
Turbulence Models ◽  
Warm Pool ◽  
Oceanic Circulation ◽  
Turbulent Mixing Layer ◽  
Numerical Instabilities

Abstract. In this paper we investigate the finite-time and asymptotic behaviour of algebraic turbulent mixing-layer models by numerical simulation. We compare the performances given by three different settings of the eddy viscosity. We consider Richardson number-based vertical eddy viscosity models. Two of these are classical algebraic turbulence models usually used in numerical simulations of global oceanic circulation, i.e. the Pacanowski–Philander and the Gent models, while the other one is a more recent model (Bennis et al., 2010) proposed to prevent numerical instabilities generated by physically unstable configurations. The numerical schemes are based on the standard finite element method. We perform some numerical tests for relatively large deviations of realistic initial conditions provided by the Tropical Atmosphere Ocean (TAO) array. These initial conditions correspond to states close to mixing-layer profiles, measured on the Equatorial Pacific region called the West-Pacific Warm Pool. We conclude that mixing-layer profiles could be considered as kinds of "absorbing configurations" in finite time that asymptotically evolve to steady states under the application of negative surface energy fluxes.

scholarly journals On the “Early-Time” Evolution of Variables Relevant to Turbulence Models for the Rayleigh-Taylor Instability

2010 ◽  
Author(s):  
Bertrand Rollin ◽  
Malcolm J. Andrews
Keyword(s):  
Turbulence Model ◽  
Initial Conditions ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Early Time ◽  
Variable Density ◽  
Taylor Instability ◽  
Turbulent Regime ◽  
Rayleigh Taylor Instability

We present our progress toward setting initial conditions in variable density turbulence models. In particular, we concentrate our efforts on the BHR turbulence model [1] for turbulent Rayleigh-Taylor instability. Our approach is to predict profiles of relevant variables before fully turbulent regime and use them as initial conditions for the turbulence model. We use an idealized model of mixing between two interpenetrating fluids to define the initial profiles for the turbulence model variables. Velocities and volume fractions used in the idealized mixing model are obtained respectively from a set of ordinary differential equations modeling the growth of the Rayleigh-Taylor instability and from an idealization of the density profile in the mixing layer. A comparison between predicted profiles for the turbulence model variables and profiles of the variables obtained from low Atwood number three dimensional simulations show reasonable agreement.

Turbulence Input Parameters Correction Methodology in Water Lubricated Thrust Bearings

2018 ◽  
Author(s):  
Xin Deng ◽  
Harrison Gates ◽  
Brian Weaver ◽  
Houston Wood ◽  
Roger Fittro
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Film Thickness ◽  
Turbulence Model ◽  
Thermal Deformation ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Water Lubrication ◽  
Low Viscosity ◽  
Eddy Viscosity Model

Oil-lubricated bearings are widely used in high speed rotating machines such as those found in the aerospace and automotive industries. However, environmental issues and risk-averse operations are resulting in the removal of oil and the replacement of all sealed oil bearings with reliable water-lubricated bearings. Due to the different fluid properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. This requires finer meshes when compared to oil-lubricated bearings as the low-viscosity fluid produces a very thin lubricant film. Analyzing water-lubricated bearings can also produce convergence and accuracy issues in traditional oil-based analysis codes. Thermal deformation largely affects oil-lubricated bearings, while having limited effects on water lubrication; mechanical deformation largely affects water lubrication, while its effects are typically lower than thermal deformation with oil. One common turbulence model used in these analysis tools is the eddy-viscosity model. Eddy-viscosity depends on the wall shear stress, therefore effective wall shear stress modeling is necessary in determining an appropriate turbulence model. Improving the accuracy and efficiency of modeling approaches for eddy-viscosity in turbulence models is of great importance. Therefore, the purpose of this study is to perform mesh refinement for water-lubricated bearings based on methodologies of eddy-viscosity modeling to improve their accuracy. According to Szeri [1], εm/v for the Boussinesq hypothesis is given by Reichardt’s formula. Fitting the velocity profile with experiments having a y+ in the range of 0–1,000 results in Ng-optimized Reichardt’s constants k = 0.4 and δ+ = 10.7. He clearly states that for y+ > 1000 theoretical predictions and experiments have a greater variance. Armentrout and others [2] developed an equation for δ+ as a function of the pivot Reynolds number, which they validated with CFD simulations. The definition of y+ can be used to approximate the first layer thickness calculated for a uniform mesh. Together with Armentrout’s equation, the number of required elements across the film thickness can be obtained. For typical turbulence models, the y+ must be within a certain range to be accurate. On the condition that the y+ is fixed to that of a standard oil bearing for which an oil bearing code was validated, the number of elements across the film thickness and coefficients used in the eddy-viscosity equation can be adjusted to allow for convergence with other fluids other than that which the traditional oil bearing code was designed for. In this study, the number of required elements across the film for improved prediction quality was calculated based on the proposed eddy-viscosity model mesh correction from the known literature. A comparison between water lubrication using the parameter correction and oil lubrication was also made. The results of this study could aid in improving future designs and models of water-lubricated bearings.

An improved turbulence model for predicting unsteady cavitating flows in centrifugal pump

2015 ◽  
Vol 25 (5) ◽  
pp. 1198-1213 ◽  
Author(s):  
Jian Wang ◽  
Yong Wang ◽  
Houlin Liu ◽  
Haoqin Huang ◽  
Linglin Jiang
Keyword(s):  
Centrifugal Pump ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulent Viscosity ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Content Type ◽  
Cavitation Inception ◽  
Cavitation Performance ◽  
Unsteady Rans

Purpose – The purpose of this paper is to study the unsteady caivitating flows in centrifugal pump, especially for improving the turbulence model to obtain highly resolution results-capable of predicting the cavitation inception, shedding off and collapse procedures. Design/methodology/approach – Both numerical simulations and experimental visualizations were performed in the present paper. An improved RCD turbulence models was proposed by considering three corrected methods: the rotating corrected method, the compressible corrected method and the turbulent viscosity corrected method. Unsteady RANS computations were conducted to compare with the experiments. Findings – The comparison of pump cavitation performance showed that the RCD turbulence model obtained better performance both in non-cavitation and cavitation conditions. The visualization of the cavitation evolution was recorded to validate the unsteady simulations. Good agreement was noticed between calculations and visualizations. It is indicated the RCD model can successfully capture the bubbles detachment and collapse at the rear of the cavity region, since it effectively reduces the eddy viscosity in the multiphase region of liquid and vapor. Furthermore, the eddy viscosity, the instantaneous pressure and density distribution were investigated. The effectiveness of the compressibility was found. Meanwhile, the influence of the rotating corrected method on prediction was explored. It is found that the RCD model solved more unsteady flow characteristics. Originality/value – The current work presented a turbulence model which was much more suitable for predicting the cavitating flow in centrifugal pump.

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

High Temperature Supersonic Jet Facility for Aeroacoustic Studies

2001 ◽  
Author(s):  
Brenton J. Greska ◽  
Anjaneyulu Krothapalli
Keyword(s):  
High Temperature ◽  
High Speed ◽  
Noise Suppression ◽  
Supersonic Jet ◽  
Infrared Camera ◽  
Operating Conditions ◽  
Laser Speckle ◽  
Stereoscopic Particle Image Velocimetry ◽  
Sudden Expansion ◽  
Jet Flows

Abstract This paper describes a newly built experimental facility at the Florida State University to develop innovative technologies for the noise suppression and mixing control of high-speed jets. This facility is capable of generating jet flows up to a maximum jet exit Mach number of about 2.5 at stagnation temperatures reaching up to 1500K. The facility can accommodate nozzles having an exit diameter of about 80 mm. At the maximum operating conditions, the jet can be run continuously for about 15 minutes. The jet exhausts into an anechoic room that measures 5.2 m (width) × 5.8 m (length) × 4 m (height). A sudden expansion (SUE) burner using Ethylene as its fuel is used to heat the high-pressure air. The instrumentation includes: High Resolution Infrared camera, stereoscopic Particle Image Velocimetry and Laser Speckle Displacement method for flow field measurements, high temperature unsteady pressure probes for the measurement of pressure fluctuations in the hydrodynamic field, and microphones with high speed data acquisition for far-field narrow band sound measurements.

Analysis of Unsteady Turbulent Merging Jet Flows With Temperature Difference

2002 ◽  
Author(s):  
Geun Jong Yoo ◽  
Won Dae Jeon
Keyword(s):  
Temperature Variation ◽  
Turbulent Flows ◽  
Turbulence Model ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Jet Flow ◽  
Reynolds Stress Model ◽  
Jet Flows ◽  
Test Cases ◽  
Temperature Variance

Suitable turbulence model is required in the course of establishing a proper analysis methodology for thermal stripping phenomena. For this purpose, three different turbulence models of k-ε model, modified k-ε model, and full Reynolds stress model and VLES are applied to analyze unsteady turbulent flows with temperature variation. Four test cases are selected for verification. These are vertical jet flows with water and sodium, parallel jet flow with sodium, and merging pipe flow through T-junction with sodium. The geometries of test cases well represent common places where thermal stripping might be occurred. The turbulence model computation shows overall jet flow characteristics well and good comparison of mean temperature distribution. Temperature variance (θ′2) is rather over-predicted, but location of high temperature variance is matched well with that of the large amplitude of temperature variation of experimental results. Meanwhile, mixing of hot and cold jet flow is found to be not that active.

scholarly journals The Effect Of Turbulence Models On Coolant Temperature And Velocity For The Pebble-Bed Typed High Temperature Reactor

KnE Energy ◽  
2016 ◽  
Vol 1 (1) ◽  
Author(s):  
Muhammad Subekti
Keyword(s):  
High Temperature ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Coolant Temperature ◽  
Face Centered Cubic ◽  
Pebble Bed ◽  
Computational Fluid Dynamics Cfd ◽  
High Temperature Reactor ◽  
The Difference ◽  
Face Centered

<p>The 3D thermal-hydraulics analysis based on Computational Fluid Dynamics (CFD) has a role to analysis more detail the reactor safety, especially for pebble-bed typed High Temperature Reactor (HTR). A realistic pebble arrangement becomes a challenge to be modeled based on the Simple Cubic (SC), Body-Centered Cubic (BCC) and Face-Centered Cubic (FCC). Furthermore, CFD calculation could utilizes laminar model as well as turbulence model such as ,  and Reynold stress model (RSM). Therefore, the objective of this reseach is to analyze the effect of turbulence model on temperature and coolant velocity distribution using FCC on pebble-bed typed HTR as well as investigation of the turbulence models. The comparison shows that all models are acceptable for HTR-10 case with the difference by the range of 0.03-0.33% for the temperature parameters, in which the minimum different is obtained by  model.</p><p> </p>

Modeling Separation-Induced Transition Using a Non-Linear Three Equation Turbulence Model and a Reynolds Stress Turbulence Model

2010 ◽  
Author(s):  
Zinon Vlahostergios ◽  
Kyros Yakinthos
Keyword(s):  
Transport Equation ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Transitional Flows ◽  
Eddy Viscosity Model ◽  
Non Linear ◽  
Stress Models

This paper presents an effort to model separation-induced transition on a flat plate with a semi-circular leading edge, by using two advanced turbulence models, the three equation non-linear model k-ε-A2 of Craft et al. [16] and the Reynolds-stress model of Craft [13]. The mechanism of the transition is governed by the different inlet velocity and turbulence intensity conditions, which lead to different recirculation bubbles and different transition onset points for each case. The use of advanced turbulence models in predicting the development of transitional flows has shown, in past studies, good perspectives. The k-ε-A2 model uses an additional transport equation for the A2 Reynolds stress invariant and it is an improvement of Craft et al. [12] non-linear eddy viscosity model. The use of the third transport equation gives improved results in the prediction of the longitudinal Reynolds stress distributions and especially, in flows where transitional phenomena may occur. Although this model is a pure eddy-viscosity model, it borrows many aspects from the more complex Reynolds-stress models. On the other hand, the use of an advanced Reynolds-stress turbulence model, such as the one of Craft [13], can predict many complex flows and there are indications that it can be applied to transitional flows also, since the crucial terms of Reynolds stress generation are computed exactly and normal stress anisotropy is resolved. The model of Craft [13], overcomes the drawbacks of the common used Reynolds-stress models regarding the computation of wall-normal distances and vectors in order to account for wall proximity effects. Instead of these quantities, it employs “normalized turbulence lengthscale gradients” which give the ability to identify the presence of strong inhomogeneity in a flow development, in an easier way. The final results of both turbulence models showed acceptable agreement with the experimental data. In this work it is shown that there is a good potential to model separation-induced transitional flows, with advanced turbulence modeling without any additional use of ad-hoc modifications or additional equations, based on various transition models.

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2¯−f Turbulence Model

2005 ◽  
Vol 127 (3) ◽  
pp. 627-634 ◽  
Author(s):  
A. Sveningsson ◽  
L. Davidson
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Mean Flow ◽  
Stator Vane ◽  
Good Agreement

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2¯−f turbulence model. Both an in-house code (CALC-BFC) and the commercial software FLUENT are used. The main objective is to investigate the v2¯−f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the end walls between two stator vanes. Results of two versions of the v2¯−f model are presented and compared to detailed mean flow field, turbulence, and heat transfer measurements. The performance of the v2¯−f model is also compared with other eddy-viscosity-based turbulence models, including a version of the v2¯−f model, available in FLUENT. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2¯−f model predictions of the vane passage flow agree well with experiments and that, among the eddy-viscosity closures investigated, the v2¯−f model, in general, performs the best. Good agreement between the two different implementations of the v2¯−f model (CALC-BFC and FLUENT) was obtained.

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