Algebraic Anisotropic Eddy-Viscosity Modeling for Application to Turbulent Film Cooling Flows

2011 ◽  
Author(s):  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Viscosity Ratio ◽  
Equation Model ◽  
Wall Region ◽  
Mean Flow ◽  
Film Cooling Effectiveness ◽  
Jet In Crossflow ◽  
Comparison Of The Results

Under-predicting the spanwise spreading of film cooling is a big problem in the film cooling computation. This is mainly due to the incorrect simulation of the spanwise transport of the jet in crossflow by conventional isotropic eddy viscosity turbulent models. An improved algebraic anisotropic eddy viscosity method including both the influence of the wall and the strain of the mean flow field to the anisotropic ratio has been raised by the authors in the paper, referred to as Algebraic Anisotropic Eddy Viscosity (AAEV) method. An equation derived from the algebraic Reynolds stress transport equations is applied to compute the anisotropic eddy-viscosity ratio. The variation of the anisotropic eddy-viscosity ratio is a function of both the dimensionless wall distance and the local mean flow field. This method is applied to the two layer k-ε model with a one-equation model in near-wall region to form a new turbulent model- AAEV k-ε model. The new model is tested for the computation of a flat plate film cooling flow with an inclined row of streamwise injected jets. Comparison of the results between the AAEV k-ε model and two-layer k-ε model with the measured adiabatic film-cooling effectiveness distributions indicates that the AAEV k-ε model can correctly predict the spanwise spreading of the film and reduce the strength of the secondary vortices.

Full Field Algebraic Anisotropic Eddy Viscosity Model for the Film Cooling Flows

2012 ◽  
Author(s):  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Wall Region ◽  
Mean Flow ◽  
Experiment Data ◽  
Anisotropic Models ◽  
Eddy Viscosity Model

The algebraic anisotropic eddy viscosity model proposed by the authors is further developed to make it suitable to the full flow field in order to focus not only in the near wall region but also in the main flow field. The three anisotropic eddy viscosity ratios for u′v′, u′w′, v′w′ are determined from the eddy viscosity hypothesis and algebraic Reynolds stress transport equations and expressed in Cartesian coordinate system. This model is applied to four isotropic two-equation turbulence models to make them anisotropic. These anisotropic models are validated with the experiment data from Sinha et al.[1]. Thorough tests are performed with all these isotropic and anisotropic turbulence models for film cooling on a flatplate with different blowing ratios. Detailed analyses of computational simulations are presented. The predicted adiabatic film cooling effectiveness and mean flow field show that the algebraic anisotropic eddy-viscosity turbulence models agree better with the experiment data. Among the four anisotropic models, the anisotropic models based on the realizable k-ε and RNG k-ε models stand out as the most promising models for flatplate film cooling predictions. It’s a big advantage of this model that it deals with the whole flow field and can be combined with different turbulence models.

Perspectives in Modeling Film Cooling of Turbine Blades by Transcending Conventional Two-Equation Turbulence Models

2002 ◽  
Vol 124 (3) ◽  
pp. 472-484 ◽  
Author(s):  
A. Azzi ◽  
D. Lakehal
Keyword(s):  
Film Cooling ◽  
Eddy Viscosity ◽  
Transport Coefficients ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Outer Core ◽  
Equation Model ◽  
Wall Region ◽  
Stress Models ◽  
Near Wall

The paper presents recent trends in modeling jets in crossflow with relevance to film cooling of turbine blades. The aim is to compare two classes of turbulence models with respect to their predictive performance in reproducing near-wall flow physics and heat transfer. The study focuses on anisotropic eddy-viscosity/diffusivity models and explicit algebraic stress models, up to cubic fragments of strain and vorticity tensors. The first class of models are direct numerical simulation (DNS) based two-layer approaches transcending the conventional k−ε model by means of a nonisotropic representation of the turbulent transport coefficients; this is employed in connection with a near-wall one-equation model resolving the semi-viscous sublayer. The aspects of this new strategy are based on known channel-flow and boundary layer DNS statistics. The other class of models are quadratic and cubic explicit algebraic stress formulations rigorously derived from second-moment closures. The stress-strain relations are solved in the context of a two-layer strategy resolving the near-wall region by means of a nonlinear one-equation model; the outer core flow is treated by use of the two-equation model. The models are tested for the film cooling of a flat plate by a row of streamwise injected jets. Comparison of the calculated and measured wall-temperature distributions shows that only the anisotropic eddy-viscosity/diffusivity model can correctly predict the spanwise spreading of the temperature field and reduce the strength of the secondary vortices. The wall-cooling effectiveness was found to essentially depend on these two particular flow features. The non-linear algebraic stress models were of a mixed quality in film-cooling calculations.

Algebraic Anisotropic Turbulence Modeling of Compound Angled Film Cooling Validated by PIV and PSP Measurements

2013 ◽  
Author(s):  
Xueying Li ◽  
Yanmin Qin ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Flow Field ◽  
Reynolds Stress ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Good Prediction ◽  
Anisotropic Model ◽  
Scalar Flux ◽  
Film Cooling Effectiveness ◽  
Anisotropic Turbulence

The complex structures in the flow field of gas turbine film cooling lead to the anisotropic property of the turbulent eddy viscosity and scalar diffusivity. An algebraic anisotropic turbulence model is developed while aiming at a more accurate modeling of the Reynolds stress and turbulent scalar flux. In this study the algebraic anisotropic model is validated by a series of in-house experiments for cylindrical film cooling with compound angle injection of 0, 45, and 90 deg. Adiabatic film cooling effectiveness and flow field are measured using PSP and PIV techniques on film cooling test rig in Tsinghua University. Detailed analyses of computational simulations are performed. The algebraic anisotropic model gives a good prediction of the secondary vortices associated with the jet and the trajectory of the jet, therefore improves the prediction of the scalar field. On one hand, the anisotropic eddy viscosity improves the modeling of Reynolds stress and the predictive flow field. On the other hand, the anisotropic turbulent scalar-flux model includes the role of anisotropic eddy viscosity in modeling of scalar flux and directly improves the turbulent scalar flux prediction.

Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation

2020 ◽  
Author(s):  
Mael Harnieh ◽  
Nicolas Odier ◽  
Jérôme Dombard ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Spatial Distribution ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Total Pressure ◽  
Mean Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Vane

Abstract The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film cooling effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such systems and if possible in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations, the geometrical complexities, high Reynolds and Mach numbers as well as boundary condition setup lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Comparisons with the experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. Balance of total pressure without the contribution of thermal effects only highlights the losses generated by the wakes and secondary flows. To overcome this limitation, SLA is adopted by investigating loss maps. Thanks to this approach, mixing losses are shown to dominate in the coolant film while aerodynamic losses dominate in the coolant pipe region.

Prediction of Film Cooling Effectiveness and Heat Transfer due to Streamwise and Compound Angle Injection on Flat Surfaces

1995 ◽  
Author(s):  
S. Neelakantan ◽  
M. E. Crawford
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Equation Model ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Flat Surfaces ◽  
Momentum Flux Ratio ◽  
Density Ratios

The distributed Yavuzkurt injection model is extended to predict the effectiveness and heat transfer coefficients for film cooling injection from a single row of holes, aligned both along the direction of the freestream and at an angle with it. The injection angles were 24° and 35°. The compound angles considered were 50.5° and 60°. The Yavuzkurt film cooling model is used in conjunction with a one-equation model to yield the effectiveness and heat transfer predictions. The density ratios considered were 1.6 and 0.95 for the effectiveness predictions and 1.0 and 0.95 for the heat transfer predictions. For the effectiveness predictions, the blowing ratios range from 0.5 to 2.5, and the momentum flux ratios from 0.16 until 3.9. The hole spacings were 3, 6, and 7.8 hole diameters. The Yavuzkurt model constants are seen to be definitely correlated with the momentum flux ratio. Correlations for the model constants are obtained in terms of the momentum flux ratio. For the heat transfer predictions, the blowing ratios ranged from 0.4 to 2.0, and the momentum flux ratios from 0.16 to 3.9. The spacing between the holes was 3, 6, and 7.8 hole diameters. The matching between the effectiveness correlations and the heat transfer predictions is done on the basis of the momentum flux ratio. Results indicate that the Yavuzkurt model predictions are best for the in-line round holes. Heat transfer predictions are close to the experimental results for lower blowing ratios, until the ratio exceeds 1. For higher blowing ratios, the predictions, though less accurate, follow the experimental trends.

Computational Study of Film-Cooling Effectiveness on a Low-Speed Airfoil Cascade: Part II — Discussion of Physics

2002 ◽  
Author(s):  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Film Cooling ◽  
Turbulence Modeling ◽  
Computational Study ◽  
Density Ratio ◽  
Leading Edge ◽  
Mean Flow ◽  
Film Cooling Effectiveness ◽  
Geometry Modeling ◽  
Blowing Ratio ◽  
Airfoil Cascade

Computational fluid dynamics (CFD) results are presented for a study of film cooling on a linear turbine airfoil cascade. The simulations are for a single-row of streamwise-injected cylindrical holes on both the pressure and suction surfaces, downstream of the leading edge. The cases considered match experimental efforts previously documented in the open literature. Results are obtained for density ratio equal to 2.0, and a blowing ratio range from 0.5 to 2.0. The computational methodology minimizes error due to geometry modeling, grid, and numerical scheme, placing the simulations against the limits of the turbulence modeling. In this part, the results are examined in order to highlight the mean-flow physical mechanisms responsible for film-cooling performance on airfoils.

Interactions Between the Combustor Swirl and the High Pressure Stator of a Turbine

2012 ◽  
Author(s):  
Lucas Giller ◽  
Heinz-Peter Schiffer
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Film Cooling ◽  
Field Measurements ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Film Cooling Holes ◽  
The Impact

The interaction between the strongly swirling combustor outflow and the high pressure turbine nozzle guide vanes were investigated at the cascade test rig at Technische Universität Darmstadt. The test section of the rig consists of six swirl generators and five cascade vanes. The three middle vanes are equipped with film cooling holes at the leading edges. The swirler nozzles are aligned with the center of the cascade passages. The operating settings are defined by the swirl number, the distance between the swirler nozzles and the vanes, the blowing ratio and the radial angle of the film cooling holes. Flow field measurements using PIV downstream of the swirlers and five hole probe measurements at the inlet and outlet plane of the cascade were accomplished. Measurements using the ammonia diazo technique to determine the adiabatic film cooling effectiveness on the surface of the center cascade vane were also carried out. It is shown that a swirling inflow leads to a strong alteration of the flow field and the losses in the passages in comparison to an axial inflow. Furthermore, the impact of the swirl on the formation of the cooling film and it’s adiabatic film cooling effectiveness is presented.

Film-Cooled Turbine Endwall in a Transonic Flow Field: Part I—Aerodynamic Measurements

2001 ◽  
Vol 123 (4) ◽  
pp. 709-719 ◽  
Author(s):  
Friedrich Kost ◽  
Martin Nicklas
Keyword(s):  
Flow Field ◽  
Transonic Flow ◽  
Film Cooling ◽  
Coolant Flow ◽  
Pressure Probe ◽  
Thermal Methods ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Oil Flow ◽  
Oil Flow Visualization

Thermodynamic and aerodynamic measurements were carried out in a linear turbine cascade with transonic flow field. Heat transfer and adiabatic film-cooling effectiveness resulting from the interaction of the flow field and the ejected coolant at the endwall were measured and will be discussed in two parts. The investigations were performed in the Windtunnel for Straight Cascades (EGG) at DLR, Go¨ttingen. The film-cooled NGV endwall was operated at representative dimensionless engine conditions of Mach and Reynolds number Ma2is=1.0 and Re2=850,000 respectively. Part I of the investigation discusses the aerodynamic measurements. Detailed aerodynamic measurements were carried out in the vicinity of a turbine stator endwall using conventional pressure measurements and a Laser-2-Focus (L2F) device. The L2F served as a velocimeter measuring 2D-velocity vectors and turbulence quantities and as a tool to determine the concentration of coolant ejected through a slot and through holes at the endwall. Pressure distribution measurements provided information on the endwall pressure field and its variation with coolant flow rate. Pressure probe measurements delivered cascade performance data. Oil flow visualization and laser velocimetry gave a picture of the near endwall flow field and its interference with the coolant. A strikingly strong interaction of coolant air and secondary flow field could be identified. The measurement of coolant concentration downstream of the ejection locations provided a detailed picture of the coolant flow convection and its mixing with the main flow. The relative coolant concentration in the flow field is directly comparable to the adiabatic film-cooling effectiveness measured by thermal methods at the wall.

Flow Dynamics and Film Cooling Effectiveness on a Non-Axisymmetric Contour Endwall in a Two-Dimensional Cascade Passage

2009 ◽  
Author(s):  
Gazi I. Mahmood ◽  
Ross Gustafson ◽  
Sumanta Acharya
Keyword(s):  
Temperature Field ◽  
Flow Field ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Blowing Ratio

The measured flow field and temperature field near a three-dimensional asymmetric contour endwall employed in a linear blade cascade are presented with and without film-cooling flow on the endwall. Flow field temperature and Nusselt number distributions along the asymmetric endwall with wall heating and no film-cooling flow are also reported to show local high heat transfer region on the endwall and justify the locations of the coolant holes. Adiabatic film-cooling effectiveness along the endwall is then measured to indicate the local effects of the coolant jets. The near endwall flow field and temperature field provide the coolant flow behavior and the interaction of coolant jets with the boundary layer flow. Thus, the local film-cooling effectiveness can be explained with the coolant jet trajectories. The measurements are obtained at the Reynolds number of 2.30×105 based on blade actual chord and inlet velocity, coolant-to-free stream temperature ratio of 0.93, and coolant-to-free stream density ratio of 1.06. The cascade employs the hub side blade section and passage geometry of the first stage rotor of GE-E3 turbine engine. The contour endwall profile is employed on the bottom endwall only in the cascade. The blowing ratio of the film-cooling flow varies from 1.0 to 2.4 from 71 discrete cylindrical holes located in the contour endwall. The three-dimensional profile of the endwall varies in height in both the pitchwise and axial directions. The flow field is quantified with the streamwise vorticity and turbulent intensity, pitchwise static pressure difference, flow yaw angle, and pitchwise velocity. Both the flow field and temperature data indicate that the coolant jets cover more distance in the pitchwise and axial direction in the passage as the blowing ratio increases. Thus, the local and average film-cooling effectiveness increase with the blowing ratio.

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