scholarly journals Effects of Various Modeling Schemes on Mist Film Cooling Simulation

2007 ◽  
Vol 129 (4) ◽  
pp. 472-482 ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Cooling Effectiveness ◽  
Air Supply ◽  
Cooling Enhancement ◽  
Simulation Results ◽  
Density Ratios ◽  
Cooling Air

Numerical simulation is performed in this study to explore film-cooling enhancement by injecting mist into the cooling air with a focus on investigating the effect of various modeling schemes on simulation results. The effect of turbulence models, dispersed-phase modeling, inclusion of different forces (Saffman, thermophoresis, and Brownian), trajectory tracking, and mist injection scheme is studied. The effect of flow inlet boundary conditions (with/without air supply plenum), inlet turbulence intensity, and the near-wall grid density on simulation results is also included. Simulation of a two-dimensional (2D) slot film cooling with a fixed blowing angle and blowing ratio shows a 2% mist (by mass) injected into the cooling air can increase the cooling effectiveness about 45%. The renormalization group (RNG) k-ε model, Reynolds stress model, and the standard k-ε turbulence model with an enhanced wall treatment produce consistent and reasonable results while the turbulence dispersion has a significant effect on mist film cooling through the stochastic trajectory calculation. The thermophoretic force slightly increases the cooling effectiveness, but the effect of Brownian force and Saffman lift is imperceptible. The cooling performance deteriorates when the plenum is included in the calculation due to the altered velocity profile and turbulence intensity at the jet exit plane. The results of this paper can provide guidance for corresponding experiments and serve as the qualification reference for future more complicated studies with 3D cooling holes, different blowing ratios, various density ratios, and rotational effect.

scholarly journals Effects of Various Modeling Schemes on Mist Film Cooling Simulation

2005 ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Turbulence Models ◽  
Cooling Effectiveness ◽  
Air Supply ◽  
Cooling Enhancement ◽  
Simulation Results ◽  
Density Ratios ◽  
Slot Film Cooling ◽  
Cooling Air

Numerical simulation is performed in this study to explore film-cooling enhancement by injecting mist into the cooling air with a focus on investigating the effect of various modeling schemes on the simulation results. The effect of turbulence models, dispersed-phase modeling, inclusion of different forces (Saffman, thermophoresis, and Brownian), trajectory tracking, and mist injection scheme is studied. The effect of flow inlet boundary conditions (with/without air supply plenum), inlet turbulence intensity, and the near-wall grid density on simulation results is also included. Using a 2-D slot film cooling simulation with a fixed blowing angle and blowing ratio shows a 2% mist injected into the cooling air can increase the cooling effectiveness about 45%. The RNG k-ε model, RSM and the standard k-ε turbulence model with the enhanced wall treatment produce consistent and reasonable results while the turbulence dispersion has a significant effect on mist film cooling through the stochastic trajectory calculation. The thermophoretic force slightly increases the cooling effectiveness, but the effect of Brownian force and Saffman lift is imperceptible. The cooling performance is affected negatively by the plenum in this study, which alters the velocity profile and turbulence intensity at the jet exit plane. The results of this paper can serve as the qualification reference for future more complicated studies including 3-D cooling holes, different blowing ratios, various density ratios, and rotational effect.

An Investigation of the Effects of Film Cooling in a High-Pressure Aeroengine Turbine Stage

2005 ◽  
Author(s):  
Kam S. Chana ◽  
Mary A. Hilditch ◽  
James Anderson
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Phase Iii ◽  
Cooling Effectiveness ◽  
Aerodynamic Efficiency ◽  
Cooling Flow ◽  
External Cooling ◽  
Improved Design ◽  
Density Ratios ◽  
Cooling Air

Cooling is required to enable the turbine components to survive and have acceptable life in the very high gas temperatures occurring in modern engines. The cooling air is bled from the compression system, with typically about 15% of the core flow being diverted in military engines and about 20% in civil turbofans. Cooling benefits engine specific thrust and efficiency by allowing higher cycle temperatures to be employed, but the bleed air imposes cycle penalties and also reduces the aerodynamic efficiency of the turbine blading, typically by 2–4%. Cooling research aims to develop and validate improved design methodologies that give maximum cooling effectiveness for minimum cooling flow. This paper documents external cooling research undertaken in the Isentropic Light Piston Facility at QinetiQ as part of a European collaborative programme on turbine aerodynamics and heat transfer. In Phase I, neither the ngv nor the rotor was cooled; cooling was added to the ngv only for Phase II, and to the rotor and ngv in Phase III. Coolant blowing rates and density ratios were also varied in the experiments. This paper describes the ILPF and summarises the results of this systematic programme, paying particular attention to the variation in aerofoil heat transfer with changing coolant conditions, and the effects coolant ejection has on the aerofoil’s aerodynamic performance.

Evaluation of Two-Equation Models of Turbulence in Predicting Film Cooling Performance Under High Free Stream Turbulence

2007 ◽  
Author(s):  
Savas Yavuzkurt ◽  
Jawad S. Hassan
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Turbulence Models ◽  
Accurate Solution ◽  
Diameter Ratio ◽  
Tube Length ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Density Ratios

The capabilities of four two-equation turbulence models in predicting film cooling effectiveness under high free stream turbulence (FST) intensity (Tu = 10%) were investigated and their performance are presented and discussed. The four turbulence models are: the standard k-ε, RNG, and realizable k-ε models as well as the standard k-ω model all four found in the FLUENT CFD code. In all models, the enhanced wall treatment has been used to resolve the flow near solid boundaries. A systematic approach has been followed in the computational setup to insure grid-independence and accurate solution that reflects the true capabilities of these models. Exact geometrical and flow-field replicas of an experimental study on discrete hole film cooling were generated and used in FLUENT. A pitch-to-diameter ratio of 3.04, injection tube length-to-diameter ratio of 4.6 and density ratios of 0.92 and 0.97 were some of the parameters used in the film cooling analysis. The study covered two levels of blowing ratios (M = 0.5 and 1.5) at an environment of what is defined as high initial free-stream turbulence intensity (Tu = 10%). Performance of these models under a very low initial FST were presented in a paper by the authors in Turbo Expo 2006. In that case, the standard k-ε model had the most consistent performance among all considered turbulence models and the best centerline film cooling effectiveness predictions under very low FST. However, after the addition of high FST in the free-stream, even the standard k-ε model started to deviate greatly from the experimental data (up to 200% over-prediction) under high blowing ratios (M = 1.5). The model which performed the best under high FST but low blowing ratios (M = 0.5) is still the standard k-ε model. In all cases only standard k-ε model results match the trends of data for both cases. It can be said that under high FST with high M all the models do not do a good job of predicting the data. It was concluded that these deviations resulted from the effects of both high FST and high M. Under high M, near the injection holes deviations could result from the limitations of Boussinesq hypothesis relating the direction of Reynolds stress to the mean strain rate. Also, it seems like all models have trouble including the effects of high FST by not being able to take into account high levels of diffusion of turbulence from the free stream. However, standard k-ε model still looks like the best candidate for further improvement with the addition of new diffusion model for TKE under high FST.

Numerical Investigations of Cooling Enhancement With Internal Ribs and External Coolant Film

2012 ◽  
Author(s):  
Zhixin Feng ◽  
Zhongwang Dou ◽  
Jianhua Wang ◽  
Shiyan Ma ◽  
Zhiqiang Zhang
Keyword(s):  
Film Cooling ◽  
Influence Factors ◽  
Numerical Approach ◽  
Cooling Effectiveness ◽  
Numerical Investigations ◽  
Wall Film ◽  
Ansys Cfx ◽  
Cooling Enhancement ◽  
Energy Equations ◽  
Cooling Air

Experimental and numerical investigations were carried out to study the average cooling performance of two different rectangular structures: 1) purely ribbed channel (only ribs were periodically embedded inner the wall of the structure); 2) combined structure of film cooling with the ribs (in the ribbed wall, film holes were periodically drilled). To create a similar environment of gas turbine blade, the experiments were performed at a high temperature mainstream, and the ambient temperature cooling air passed through the channel with the direction normal to the mainstream. In the experimental and numerical investigations, the overall cooling effect contributed by the heat conduction through channel’s wall and convections including internal ribbed wall and external film cooling was considered. In the numerical investigation, 3D conservation equations including mass, momentum, energy, turbulence eddy frequency and turbulence kinetic energy equations were solved with ANSYS-CFX, and the hybrid mesh technique and shear stress transport (SST) k-ω model were adopted. This numerical approach was validated by the experimental data. Using the validated numerical approach, the influence factors on the overall cooling effectiveness are discussed, and the effects of the internal ribs and external film cooling are numerically compared by the two structures. The relationship of the overall cooling effectiveness averaged over the rectangular surface with the mainstream Reynolds number, mass flow ratio and temperature ratio of the mainstream to cooling air, as well as the blowing ratio injected through the film holes was fitted by the numerical results.

scholarly journals Combined Experimental and CFD Investigation of Flat Plate Film Cooling through Fan Shaped Holes

2019 ◽  
Vol 4 (2) ◽  
pp. 7 ◽  
Author(s):  
Samaneh Rouina ◽  
Silvia Ravelli ◽  
Giovanna Barigozzi
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Thermal Protection ◽  
Density Ratio ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Film Cooling Effectiveness ◽  
Cooling Air ◽  
Low Speed Wind Tunnel

The present paper reports the results of an experimental and computational investigation of flat plate film cooling jets discharged from three fan-shaped holes. Measurements have been carried out at near unity density ratio in a low-speed wind tunnel, at low inlet turbulence intensity, with blowing ratios (BR) of 1 and 2. Aerodynamic results have shown that the jet stays attached to the flat plate. Thermal measurements have revealed that film cooling effectiveness decreases downstream of the holes, and BR equal to 1 provides the best trade-off between cooling air consumption and thermal protection. Consequently, BR = 1 was selected for assessing the performance of different turbulence models, implemented in STAR-CCM+, according with the steady Reynolds-averaged Navier–Stokes (RANS) approach. Predictions from realizable k-ε (RKE), shear stress transport k-ω (SST KW) and Reynolds stress model (RSM) were compared against measurements of laterally averaged and centerline adiabatic effectiveness, as well as off-the-wall velocity maps and profiles of stress components. RSM provided the most accurate predictions.

Influence of Freestream Turbulence Intensity on Cooling Effectiveness

2001 ◽  
Author(s):  
E. Laroche
Keyword(s):  
Turbulence Intensity ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Temperature Fields ◽  
Type Model ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Flow Parameters ◽  
Injection Region ◽  
Correct Estimation

The objective of the study is to evaluate the potential of various turbulence models to simulate satisfactorily the influence of freestream turbulence intensity on the development of a cooling film, via a coupled computation, i.e. taking into account the full geometry (plenum, hole and main channel). Isotropic as well as anisotropic turbulence models (for the velocity as well as for the temperature fields) are tested, and an insight on the best suited closure is expected. The question of the respective influences of the various flow parameters (boundary layer characteristics, turbulent length scales, mass blowing ratios…) is also addressed. A low Reynolds number approach gives a correct estimation of the cooling effectiveness after approximately 10 hole diameters, for high or small blowing ratios, and using a k-ε model. The standard k-1 model largely underestimates the mixing in the injection region. The prediction of the injection region still needs to be improved for most configurations, but qualitatively the computation seems more than acceptable, as it exhibits the classically identified counter-rotating vortices that drive the heat transfer phenomena. The study also showed that predicting the influence of the freestream turbulence intensity requires taking into account thermal anisotropies, using an EARSMt (Explicit Algebraic Reynolds Stress Model, t being for Thermal) type model. An increase in freestream turbulence intensity was then shown to diminish the cooling effectiveness for all blowing ratios. The magnitude of the drop has still to be satisfactorily captured.

scholarly journals Performance of Turbulence Models and Near-Wall Treatments in Discrete Jet Film Cooling Simulations

1998 ◽  
Author(s):  
Jeffrey D. Ferguson ◽  
Dibbon K. Walters ◽  
James H. Leylek
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Turbulence Models ◽  
Viscous Sublayer ◽  
Reynolds Stress Model ◽  
Quality Data ◽  
Wall Functions ◽  
First Time ◽  
Near Wall ◽  
Non Equilibrium

For the first time in the open literature, code validation quality data and a well-tested, highly reliable computational methodology are employed to isolate the true performance of seven turbulence treatments in discrete jet film cooling. The present research examines both computational and high quality experimental data for two length-to-diameter ratios of a row of streamwise injected, cylindrical film holes. These two cases are used to document the performance of the following turbulence treatments: 1) standard k-ε model with generalized wall functions; 2) standard k-ε model with non-equilibrium wall functions: 3) Renormalization Group k-ε (RNG) model with generalized wall functions; 4) RNG model with non-equilibrium wall functions: 51 standard k-ε model with two-layer turbulence wall treatment; 6) Reynolds Stress Model (RSM) with generalized wall functions; and 7) RSM with non-equilibrium wall functions. Overall, the standard k-ε turbulence model with the two-layer near-wall treatment, which resolves the viscous sublayer, produces results that are more consistent with experimental data.

A Parametric Numerical Study of the Effects of Freestream Turbulence Intensity and Length Scale on Anti-Vortex Film Cooling Design at High Blowing Ratio

2013 ◽  
Author(s):  
Timothy W. Repko ◽  
Andrew C. Nix ◽  
James D. Heidmann
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Numerical Study ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Length Scales ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Design

An advanced, high-effectiveness film-cooling design, the anti-vortex hole (AVH) has been investigated by several research groups and shown to mitigate or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low freestream turbulence levels. [1, 2] The effects of increased turbulence on the AVH geometry were previously investigated and presented by researchers at West Virginia University (WVU), in collaboration with NASA, in a preliminary CFD study [3] on the film effectiveness and net heat flux reduction (NHFR) at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. The current paper presents the results of an extended numerical parametric study, which attempts to separate the effects of turbulence intensity and length-scale on film cooling effectiveness of the AVH. In the extended study, higher freestream turbulence intensity and larger scale cases were investigated with turbulence intensities of 5, 10 and 20% and length scales based on cooling hole diameter of Λx/dm = 1, 3 and 6. Increasing turbulence intensity was shown to increase the centerline, span-averaged and area-averaged adiabatic film cooling effectiveness. Larger turbulent length scales were shown to have little to no effect on the centerline, span-averaged and area-averaged adiabatic film-cooling effectiveness at lower turbulence levels, but slightly increased effect at the highest turbulence levels investigated.

Film Cooling of the Gas Turbine Endwall by Discrete-Hole Injection

1996 ◽  
Vol 118 (2) ◽  
pp. 278-284 ◽  
Author(s):  
M. Y. Jabbari ◽  
K. C. Marston ◽  
E. R. G. Eckert ◽  
R. J. Goldstein
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Hole Injection ◽  
Qualitative Information ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Density Ratios

Film cooling performance for injection through discrete holes in the endwall of a turbine blade is investigated. The effectiveness is measured at 60 locations in the region covered by injection. Three nominal blowing rates, two density ratios, and two approaching flow Reynolds numbers are examined. Analysis of the data reveals that even 60 locations are insufficient for the determination of the field of film cooling effectiveness with its strong local variations. Visualization of the traces of the coolant jets on the endwall surface, using ammonium-diazo-paper, provides useful qualitative information for the interpretation of the measurements, revealing the paths and interaction of the jets, which change with blowing rate and density ratio.

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