Computational Study of the Effects of Shock Waves on Film Cooling Effectiveness

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
C. X.-Z. Zhang ◽  
I. Hassan
Keyword(s):  
Shock Waves ◽  
Flat Plate ◽  
Film Cooling ◽  
Computational Study ◽  
Strong Shock ◽  
Boundary Layer Separation ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Transonic Airfoil

The performance of a louver cooling scheme on a transonic airfoil has been studied numerically in this paper. Film cooling holes are located near the passage throat. The Mach number at the location of the jet exit is close to unity. A comparison of film cooling effectiveness between numerical prediction and experimental data for a circular hole shows that the numerical procedures are adequate. In addition to the shock-wave effects and compressibility, curvature effect was also studied by comparing cooling effectiveness on the airfoil surface with that on a flat plate. Substantially higher cooling effectiveness for the louver cooling scheme on the airfoil was predicted at blowing ratios below 1 in comparison to other cooling configurations. At higher blowing ratios than 2 the advantages of the louver cooling scheme become less obvious. It was also found that for the same cooling configuration the cooling effectiveness on the transonic airfoil is slightly higher than that on a flat plate at moderately low blowing ratios below 1. At high blowing ratios above 2 when the oblique shock becomes detached from the leading edge of the hole exits, dramatic reduction in cooling effectiveness occurs as a result of boundary layer separation due to the strong shock waves. A coolant-blockage and shaped-wedge similarity was proposed and found to be able to qualitatively explain this phenomenon satisfactorily.

Computational Study of the Effects of Shock Waves on Film Cooling Effectiveness

2009 ◽  
Author(s):  
Chad X.-Z. Zhang ◽  
Ibrahim G. Hassan
Keyword(s):  
Shock Waves ◽  
Flat Plate ◽  
Film Cooling ◽  
Computational Study ◽  
Strong Shock ◽  
Boundary Layer Separation ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Transonic Airfoil

The performance of a louver cooling scheme on a transonic airfoil has been studied numerically in this paper. Film cooling holes are located near the passage throat. The Mach number at the location of the jet exit is close to unity. A comparison of film cooling effectiveness between numerical prediction and experimental data for a circular hole shows that the numerical procedures are adequate. In addition to the shock wave effects and compressibility, curvature effect was also studied by comparing cooling effectiveness on the airfoil surface with that on a flat plate. Substantially higher cooling effectiveness for the louver cooling scheme on the airfoil was predicted at blowing ratios below 1 in comparison to other cooling configurations. At higher blowing ratios than 2 the advantages of the louver cooling scheme becomes less obvious. It was also found that for the same cooling configuration the cooling effectiveness on the transonic airfoil is slightly higher than that on a flat plate at moderately low blowing ratios below 1. At high blowing ratios above 2 when the oblique shock becomes detached from the leading edge of the hole exits, dramatic reduction in cooling effectiveness occurs as a result of boundary layer separation due to the strong shock waves. A coolant-blockage and shaped-wedge analogy was proposed and found to be able to qualitatively explain this phenomenon satisfactorily.

Computational Study of Parameters Affecting Turbulent Flat Plate Film Cooling

2004 ◽  
Author(s):  
Shadi Mahjoob ◽  
Mohammad Taeibi-Rahni
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Gas Turbines ◽  
Computational Study ◽  
Velocity Ratio ◽  
Hole Injection ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle

Blade film cooling is one of the best methods to improve efficiency of gas turbines. In this work, two different methods of film cooling, namely, slot injection and discrete hole injection have been numerically studied on a flat plate. Incompressible, stationary, viscous, turbulent flow has been simulated using the FLUENT CFD code with the standard k-ε model. The study of injection angle and velocity ratio show that the optimum film cooling in both methods, occurs at the jet angle of 30° but with the velocity ratio of 1.5 for slot case and 0.5 for discrete hole case. The study of jet aspect ratio in discrete hole method, shows that stretching the hole in spanwise direction increases the film cooling effectiveness. Because it not only cool a larger region in both spanwise and streamwise directions, but also can sustain the cooled flow closer to the blade’s wall. The study of jet spacing shows that increasing the jet spacing decreases the effectiveness but not as much as jet aspect ration does.

Experimental Investigation of Turbine Phantom Cooling on Suction Side With Combustor-Turbine Leakage Gap Flow and Endwall Film Cooling

2012 ◽  
Author(s):  
Yang Zhang ◽  
Xin Yuan
Keyword(s):  
Film Cooling ◽  
Incidence Angle ◽  
Suction Side ◽  
Leakage Flow ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Coolant Injection ◽  
Passage Vortex

The film cooling injection on Hp turbine component surface is strongly affected by the complex flow structure in the nozzle guide vane or rotor blade passages. The action of passage vortex near endwall surface could dominate the film cooling effectiveness distribution on the component surfaces. The film cooling injections from endwall and airfoil surface are mixed with the passage vortex. Considering a small part of the coolant injection from endwall will move towards the airfoil suction side and then cover some area, the interaction between the coolants injected from endwall and airfoil surface is worth investigating. Though the temperature of coolant injection from endwall increases after the mixing process in the main flow, the injections moving from endwall to airfoil suction side still have the potential of second order cooling. This part of the coolant is called “Phantom cooling flow” in the paper. A typical scale-up model of GE-E3 Hp turbine NGV is used in the experiment to investigate the cooling performance of injection from endwall. Instead of the endwall itself, the film cooling effectiveness is measured on the airfoil suction side. This paper is focused on the combustor-turbine interface gap leakage flow and the coolant from fan-shaped holes moving from endwall to airfoil suction side. The coolant flow is injected at a 30deg angle to the endwall surface both from a slot and four rows of fan-shaped holes. The film cooling holes on the endwall and the leakage flow are used simultaneously. The blowing ratio and incidence angle are selected to be the parameters in the paper. The experiment is completed with the blowing ratio changing from M = 0.7 to M = 1.3 and the incidence angle varying from −10deg to +10deg, with inlet Reynolds numbers of Re = 3.5×105 and an inlet Mach number of Ma = 0.1.

Numerical modeling of innovative film cooling hole schemes

2021 ◽  
Author(s):  
Siavash Khajehhasani
Keyword(s):  
Flat Plate ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Lateral Spread ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Mainstream Flow ◽  
Hole Geometry

A numerical investigation of the film cooling performance on novel film hole schemes is presented using Reynolds-Averaged Navier-Stokes analysis. The investigation considers low and high blowing ratios for both flat plate film cooling and the leading edge of a turbine blade. A novel film hole geometry using a circular exit shaped hole is proposed, and the influence of an existing sister holes’ technique is investigated. The results indicate that high film cooling effectiveness is achieved at higher blowing ratios, results of which are even greater when in the presence of discrete sister holes where film cooling effectiveness results reach a plateau. Furthermore, a decrease in the strength of the counter-rotating vortex pairs is evident, which results in more attached coolant to the plate’s surface and a reduction in aerodynamic losses. Modifications are made to the spanwise and streamwise locations of the sister holes around the conventional cylindrical hole geometry. It is found that the spanwise variations have a significant influence on the film cooling effectiveness results, while only minor effects are observed for the streamwise variations. Positioning the sister holes in locations farther from the centerline increases the lateral spreading of the coolant air over the plate’s surface. This result is further verified through the flow structure analysis. Combinations of sister holes are joined with the primary injection hole to produce innovative variant sister shaped single-holes. The jet lift-off is significantly decreased for the downstream and up/downstream configurations of the proposed scheme for the flat plate film cooling. These schemes have shown notable film cooling improvements whereby more lateral distribution of coolant is obtained and less penetration of coolant into the mainstream flow is observed. The performance of the sister shaped single-holes are evaluated at the leading edge of a turbine blade. At the higher blowing ratios, a noticeable improvement in film cooling performance including the effectiveness and the lateral spread of the cooling air jet has been observed for the upstream and up/downstream schemes, in particular on the suction side. It is determined that the mixing of the coolant with the high mainstream flow at the leading edge of the blade is considerably decreased for the upstream and up/downstream configurations and more adhered coolant to the blade’s surface is achieved.

Effect of Density Ratio on Film-Cooling Effectiveness Distribution and Its Uniformity for Several Hole Geometries on a Flat Plate

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Lateral Spread ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Density Ratios ◽  
Compound Angle

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.

Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film-Cooling

2018 ◽  
Author(s):  
Zachary T. Stratton ◽  
Tom I-P. Shih
Keyword(s):  
Shear Layer ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Turbulent Structure ◽  
Reverse Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Turbulent Fluctuations

Large eddy simulations (LES) were performed to investigate film cooling of a flat plate, where the cooling jets issued from a plenum through one row of circular holes of diameter D and length 4.7D that are inclined at 35° relative to the plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated — one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair. At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.

Systematic Study on the Fluid Dynamical Behaviour of Streamwise and Laterally Inclined Jets in Crossflow

1997 ◽  
Author(s):  
R.-D. Baier ◽  
W. Koschel ◽  
K.-D. Broichhausen ◽  
G. Fritsch
Keyword(s):  
High Resolution ◽  
Film Cooling ◽  
Large Scale ◽  
Computational Study ◽  
Dynamical Behaviour ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes

The design of discrete film cooling holes for gas turbine airfoil applications is governed by a number of parameters influencing both their aerodynamic and thermal behaviour. This numerical and experimental study focuses on the marked differences between film cooling holes with combined streamwise and lateral inclination and film cooling holes with streamwise inclination only. The variation in the blowing angle was chosen on a newly defined and physically motivated basis. High resolution low speed experiments on a large scale turbine airfoil gave insights particularly into the intensified mixing process with lateral ejection. The extensive computational study is performed with the aid of a 3D block-structured Navier-Stokes solver incorporating a low-Reynolds-number k-ε turbulence model. Special attention is paid to mesh generation as a precondition for accurate high-resolution results. The downstream temperature fields of the jets show reduced spanwise variations with increasing lateral blowing angle; these variations are quantified for a comprehensive variety of configurations in terms of adiabatic film cooling effectiveness.

Experimental Film Cooling Effectiveness of Multi-Row Patterns on Flat and Step-Down Surfaces

2019 ◽  
Author(s):  
Filippo Baldino ◽  
Mohammad E. Taslim
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Hole Diameter ◽  
Constant Density ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flat Surfaces ◽  
Step Down ◽  
Turbine Airfoils

Abstract Multiple rows of film cooling holes have been widely used for the protection of gas turbine airfoils and other hot sections. In the common approach, however, the streamwise surfaces between the film holes may not receive enough protection. The objective of this research was to overcome this issue by introducing a new layout of film cooling, the step-down surfaces. Pressure-sensitive paint technique was used to test three pairs of geometries. Each pair consists of a flat and a step-down surface for back to back comparisons, under otherwise identical conditions. Two rows of 30° angled cylindrical holes of 3.175 mm diameter, exiting at the step bottom corner, introduced the coolant to the surface. Two spanwise pitch-to-diameter ratios of 2 and 4, two row distance to hole diameter of 4 and 8, four blowing ratios of 0.25, 0.5, 0.75 and 1, all at a constant density ratio of 1 were tested. Adding a step-down of the order of 0.8 hole-diameter proved to significantly increase the overall film cooling effectiveness. Two major improvements compared to a flat surfaces were observed: (a) longer streamwise film cooling effectiveness (b) more uniform spanwise distribution of coolant. The main reason of all the improvements is the aerodynamic phenomenon governing the flow evolution, the Coanda effect. The latter, indeed, enhances the flow attachment to the airfoil surface downstream the step.

Geometrical Optimization and Experimental Validation of a Tripod Film Cooling Hole With Asymmetric Side Holes

2014 ◽  
Author(s):  
Zhongran Chi ◽  
Chang Han ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Experimental Results ◽  
Geometrical Parameters ◽  
Vortex System ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Optimum Configuration ◽  
Optimization Study ◽  
Cooling Hole

A tripod cylindrical film hole with asymmetric side holes is studied numerically and experimentally on a flat plate for higher film cooling effectiveness. Firstly, the influences of geometrical parameters are studied and the optimum configurations of the asymmetric tripod hole are found in a DoE optimization study based on an improved numerical model for film cooling prediction, in which more than one hundred 3D CFD simulations are carried out. Then one optimum configuration of the asymmetric tripod hole is examined experimentally using pressure-sensitive paint (PSP) measurements, and compared against the experimental results of the simple cylindrical film hole and a well-designed shaped film hole. The flow and heat transfer characteristics of the asymmetric tripod holes were explored from the DoE results. The side holes can form a shear vortex system or an anti-kidney vortex system when proper spanwise distances of them are adopted, which laterally transports the coolant and form a favorable coolant coverage. According to the experimental results, the cooling performance of the optimized asymmetric tripod hole is significantly better than that of the simple cylindrical hole, especially at high blowing ratios. And the optimized asymmetric tripod hole can provide almost the same or even higher film cooling effectiveness on the flat plate compared with the shaped hole in the same flow conditions.

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