Evaluation of the SST-SAS Model for Prediction of Separated Flow Inside Turbine Internal Cooling Passages

2016 ◽  
Author(s):  
Piotr Zacharzewski ◽  
Kathy Simmons ◽  
Richard Jefferson-Loveday ◽  
Luigi Capone
Keyword(s):  
Heat Transfer ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Separated Flow ◽  
Streamwise Velocity ◽  
Stream Velocity ◽  
Internal Cooling ◽  
Sas Model ◽  
The Hill

The flow and heat transfer over a three-dimensional axisymmetric hill and rectangular ribbed duct is computed in order to evaluate the Shear Stress Transport - Scale Adaptive Simulation (SST-SAS) turbulence model. The study presented here is relevant to turbine blade internal cooling passages and the aim is to establish whether SAS-SST is a viable alternative to other turbulence models for computations of such flows. The model investigated is based on Menter’s modification to Rotta’s k-kL model and comparison is made against experimental data as well as other models including some with scale resolving capability, such as LES, DES & hybrid LES-RANS. For the hill case the SAS model dramatically overpredicts the size of the separation bubble. The LES on the other hand proved to be more accurate even though the mesh is courser by LES standards. There is little improvement of SST-SAS compared with RANS. Broadly speaking all models predict streamwise velocity profiles for the ribbed channel with reasonable accuracy. The cross-stream velocity is underpredicted by all models. Heat transfer prediction is more accurately predicted by LES than RANS, DES & SST-SAS on a mesh that is slightly coarser than required by LES standard, however it still exhibits significant error. It is concluded that more investigation of the SST-SAS model is required to more broadly assess its viability for industrial computation.

Three Dimensional Measurements of Instantaneous Flow Field in Corners With Smooth Surfaces Under a Zero Pressure Gradient

2004 ◽  
Author(s):  
Michael Phillips ◽  
Steve Deutsch ◽  
Arnie Fontaine ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Instantaneous Velocity ◽  
Stream Velocity ◽  
Internal Cooling ◽  
Mean Velocity ◽  
Data Set ◽  
Corner Flow

Three dimensional instantaneous velocity data were taken in a turbulent corner flow with smooth walls under a zero pressure gradient. Experiments were carried out in air with a free stream velocity of 13 m/s and an axial Reynolds number of about 10,000,000. The data were collected using a three-component LDV system that was configured in a nearly orthogonal setup. Measurements were made down to a y+ of approximately 5, and should provide a valuable data set in developing models and predictive codes. Data were collected at two axial locations, 0.93 and 1.26 m measured from the virtual origin. The boundary layer thickness was 20.90 mm and 24.91 mm respectively at these locations. At each position, instantaneous velocity profiles were measured at 6.35, 12.7, 20.6, 41.2, 82.3, 121.9, 164.5, 184.8, and 205.1 mm from the corner. The centerline profiles agree well with classical flat plate data. Three mean velocity and six Reynolds stress components have been calculated. The instantaneous velocity field data set is sufficient to compute higher order correlations. The data will be valuable for development of computer codes and models for heat transfer studies in the internal cooling channels of gas turbine blades and turbine end wall flow and heat transfer studies. An analysis of the data is presented. Future studies will concentrate on one smooth and one rough wall corner flow with favorable and adverse pressure gradients to provide a detailed database for corner flows in complex three dimensional flow fields.

scholarly journals Development of a Thermal and Structural Analysis Procedure for Cooled Radial Turbines

1988 ◽  
Author(s):  
Ganesh N. Kumar ◽  
Russell G. Deanna
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Internal Flow ◽  
Stream Velocity ◽  
Internal Cooling ◽  
Nasa Lewis Research ◽  
Transfer Coefficients ◽  
Cooling Flow ◽  
Radial Turbine

A procedure for computing the rotor temperature and stress distributions in a cooled radial turbine is considered. Existing codes for modeling the external mainstream flow and the internal cooling flow are used to compute boundary conditions for the heat transfer and stress analyses. An inviscid, quasi three-dimensional code computes the external free stream velocity. The external velocity is then used in a boundary layer analysis to compute the external heat transfer coefficients. Coolant temperatures are computed by a viscous one-dimensional internal flow code for the momentum and energy equation. These boundary conditions are input to a three-dimensional heat conduction code for calculation of rotor temperatures. The rotor stress distribution may be determined for the given thermal, pressure and centrifugal loading. The procedure is applied to a cooled radial turbine which will be tested at the NASA Lewis Research Center. Representative results from this case are included.

scholarly journals Comparison of Two-Equation Turbulence Models for Prediction of Heat Transfer on Film-Cooled Turbine Blades

1997 ◽  
Author(s):  
Vijay K. Garg ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Computer Time ◽  
Suction Surface ◽  
The Heat Transfer Coefficient

A three-dimensional Navier-Stokes code has been used to compute the heat transfer coefficient on two film-cooled turbine blades, namely the VKI rotor with six rows of cooling holes including three rows on the shower head, and the C3X vane with nine rows of holes including five rows on the shower head. Predictions of heat transfer coefficient at the blade surface using three two-equation turbulence models, specifically, Coakley’s q-ω model, Chien’s k-ε model and Wilcox’s k-ω model with Menter’s modifications, have been compared with the experimental data of Camci and Arts (1990) for the VKI rotor, and of Hylton et al. (1988) for the C3X vane along with predictions using the Baldwin-Lomax (B-L) model taken from Garg and Gaugler (1995). It is found that for the cases considered here the two-equation models predict the blade heat transfer somewhat better than the B-L model except immediately downstream of the film-cooling holes on the suction surface of the VKI rotor, and over most of the suction surface of the C3X vane. However, all two-equation models require 40% more computer core than the B-L model for solution, and while the q-ω and k-ε models need 40% more computer time than the B-L model, the k-ω model requires at least 65% more time due to slower rate of convergence. It is found that the heat transfer coefficient exhibits a strong spanwise as well as streamwise variation for both blades and all turbulence models.

Numerical Simulations of Heat Transfer and Fluid Flow for a Rotating High-Pressure Turbine

2006 ◽  
Author(s):  
F. Mumic ◽  
L. Ljungkruna ◽  
B. Sunden
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Fluid Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulence Models ◽  
High Pressure Turbine ◽  
Experimental Heat ◽  
Commercial Code ◽  
Stator Vane

In this work, a numerical study has been performed to simulate the heat transfer and fluid flow in a transonic high-pressure turbine stator vane passage. Four turbulence models (the Spalart-Allmaras model, the low-Reynolds-number realizable k-ε model, the shear-stress transport (SST) k-ω model and the v2-f model) are used in order to assess the capability of the models to predict the heat transfer and pressure distributions. The simulations are performed using the FLUENT commercial software package, but also two other codes, the in-house code VolSol and the commercial code CFX are used for comparison with FLUENT results. The results of the three-dimensional simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. It is observed that the predictions of the vane pressure field agree well with experimental data, and that the pressure distribution along the profile is not strongly affected by choice of turbulence model. It is also shown that the v2-f model yields the best agreement with the measurements. None of the tested models are able to predict transition correctly.

scholarly journals Direct numerical simulation of heat transfer from the stagnation region of a heated cylinder affected by an impinging wake

2011 ◽  
Vol 669 ◽  
pp. 64-89 ◽  
Author(s):  
JAN G. WISSINK ◽  
WOLFGANG RODI
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Three Dimensional ◽  
Stream Velocity ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Vortical Structures ◽  
Free Stream Turbulence ◽  
Heated Cylinder ◽  
Three Dimensional Simulations

The effect of an incoming wake on the flow around and heat transfer from the stagnation region of a circular cylinder was studied using direct numerical simulations (DNSs). Four simulations were carried out at a Reynolds number (based on free-stream velocity and cylinder diameterD) ofReD= 13200: one two-dimensional (baseline) simulation and three three-dimensional simulations. The three-dimensional simulations comprised a baseline simulation with a uniform incoming velocity field, a simulation in which realistic wake data – generated in a separate precursor DNS – were introduced at the inflow plane and, finally, a simulation in which the turbulent fluctuations were removed from the incoming wake in order to study the effect of the mean velocity deficit on the heat transfer in the stagnation region. In the simulation with realistic wake data, the incoming wake still exhibited the characteristic meandering behaviour of a near-wake. When approaching the regions immediately above and below the stagnation line of the cylinder, the vortical structures from the wake were found to be significantly stretched by the strongly accelerating wall-parallel (circumferential) flow into elongated vortex tubes that became increasingly aligned with the direction of flow. As the elongated streamwise vortical structures impinge on the stagnation region, on one side they transport cool fluid towards the heated cylinder, while on the other side hot fluid is transported away from the cylinder towards the free stream, thereby increasing the heat transfer. The DNS results are compared with various semi-empirical correlations for predicting the augmentation of heat transfer due to free-stream turbulence.

Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances

2013 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Free Stream ◽  
Separation Bubble ◽  
Cross Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Domain ◽  
Free Stream Turbulence ◽  
Gap Height

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.

Finite-amplitude three-dimensional instability of inviscid laminar boundary layers

1995 ◽  
Vol 290 ◽  
pp. 203-212
Author(s):  
Melvin E. Stern
Keyword(s):  
Three Dimensional ◽  
Streamwise Velocity ◽  
Finite Amplitude ◽  
Transition To Turbulence ◽  
Stream Velocity ◽  
Normal Velocity ◽  
Laminar Boundary Layers ◽  
Vertical Thickness ◽  
Layer Flow ◽  
Dimensional Instability

An inviscid laminar boundary layer flow Û(ŷ) with vertical thickness λy, and free stream velocity U is disturbed at time $\tcirc$ = 0 by a normal velocity $\vcirc$ and by a spanwise velocity ŵ([xcirc ],ŷ, $\zcirc$, 0) of finite amplitude αU, with spanwise ($\zcirc$) scale λz, and streamwise ([xcirc ]) scale λx = λz/α; the streamwise velocity û([xcirc ],ŷ,$\zcirc$,$\tcirc$) is initially undisturbed. A long wave λy/λz → 0) expansion of the Euler equations for fixed α and time scale $\tcirc$s = U−1λz/α results in a hyperbolic equation for Lagrangian displacements ŷ. Within the interval $\tcirc$ > $\tcirc$s of asymptotic validity, finite parcel displacements (O(λy)) with finite (O(U)) û fluctuations occur, independent of α no matter how small; the basic flow Û is therefore said to be unstable to streaky (λx [Gt ] λz) spanwise perturbations. The temporal development of the ('spot’) region in the (x,z) plane wherein inflected û profiles appear is computed and qualitatively related to observations of ‘breakdown’ and transition to turbulence in the flow over a flat plate. The maximum $\vcirc$([xcirc ],ŷ,$\zcirc$,$\tcirc$) increases monotonically to infinity as $\tcirc$ → $\tcirc$s.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

Numerical Simulation of Heat Transfer Characteristics for Two Metallic TPS Structures

2010 ◽  
Vol 156-157 ◽  
pp. 1568-1573
Author(s):  
Hai Yong Liu ◽  
Hong Fu Qiang
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Heat Conductivity ◽  
Radiation Effect ◽  
Thermal Protection ◽  
Heating Temperature ◽  
Three Dimensional ◽  
Metallic Layer ◽  
Internal Cooling ◽  
Thermal Radiation Effect

Two structures of metallic thermal protection system(TPS) for hypersonic vehicle were presented. One model was a multi-layer construction and the other has cavities in the metallic layer. Numerical simulations were conducted on the three-dimensional TPS models using CFD software of Gambit and Fluent. Two heating temperatures of 1073K and 773K with constant temperature and isothermal boundary conditions were considered. Heat transfer was treated as single conductivity and thermal radiation effect was not involved. The results of simulation investigation showed that: The metallic layer had poor capability to restrict the heat conductivity. Heat was easier to transfer across the bracket into the internal part of the TPS. The ability of cavities in metallic layer to resist heat conductivity was limited. The temperature-heating time variation pattern was similar for different external heating temperature. Internal cooling was important for the TPS. The thermal radiation effect on the TPS would be focused in further research.

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