NUMERICAL ASSESSMENT OF DENSITY RATIO AND MAINSTREAM TURBULENCE EFFECTS ON LEADING EDGE FILM COOLING: HEAT AND MASS TRANSFER METHODS

2021 ◽  
pp. 1-29
Author(s):  
Silvia Ravelli ◽  
Hamed Abdeh ◽  
Giovanna Barigozzi
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Transport Model ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Thermal Method ◽  
Detached Eddy Simulation ◽  
Experimental Database

Abstract Within the context of leading edge film cooling in a high-pressure turbine vane, the present study is a step forward towards modelling showerhead performance for a baseline geometry (namely 4 staggered rows of cylindrical holes) at engine like conditions, starting from a previous investigation, at low speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6% and density ratio of DR ∼ 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aero-thermal features of the flow in the leading edge region at larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness obtained by using the pressure sensitive paint (PSP) technique. DDES predictions were computed by means of the species transport model (i.e. mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e. heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I and Tu1 should be taken into account when the goal is matching engine-like conditions.

Numerical Assessment of Density Ratio and Mainstream Turbulence Effects on Leading Edge Film Cooling: Heat and Mass Transfer Methods

2020 ◽  
Author(s):  
S. Ravelli ◽  
H. Abdeh ◽  
G. Barigozzi
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Transport Model ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Thermal Method ◽  
Detached Eddy Simulation ◽  
Experimental Database

Abstract Within the context of leading edge film cooling in a high-pressure turbine vane, the present study is a step forward towards modelling showerhead performance for a baseline geometry (namely 4 staggered rows of cylindrical holes) at engine like conditions, starting from a previous investigation, at low speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6% and density ratio of DR ∼ 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aero-thermal features of the flow in the leading edge region in the presence of larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness (η), obtained by using the pressure sensitive paint (PSP) technique. DDES predictions of η were computed by means of the species transport model (i.e. mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e. heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I and Tu1 should be taken into account when the goal is matching engine-like conditions.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR = 1.1 and 1.6 over a range of blowing conditions, 0.2 ≤ M ≤ 1.5 and 0.05 ≤ I ≤ 1.2. Two different mainstream turbulence intensity levels, Tu∞ = 0.5% and 20%, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50° injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M < 0.5 there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

Experimental Evaluation of Thermal and Mass Transfer Techniques to Measure Adiabatic Effectiveness With Various Coolant to Freestream Property Ratios

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Adiabatic Wall ◽  
Thermal Methods ◽  
Turbine Cooling ◽  
Fluid Properties ◽  
Gas Turbine Cooling ◽  
Adiabatic Effectiveness

Experimentally evaluating gas turbine cooling schemes is generally prohibitive at engine conditions. Thus, researchers conduct film cooling experiments near room temperature and attempt to scale the results to engine conditions. An increasingly popular method of evaluating adiabatic effectiveness employs pressure sensitive paint (PSP) and the heat–mass transfer analogy. The suitability of mass transfer methods as a substitute for thermal methods is of interest in the present work. Much scaling work has been dedicated to the influence of the coolant-to-freestream density ratio (DR), but other fluid properties also differ between experimental and engine conditions. Most notably in the context of an examination of the ability of PSP to serve as a proxy for thermal methods are the properties that directly influence thermal transport. That is, even with an adiabatic wall, there is still heat transfer between the freestream flow and the coolant plume, and the mass transfer analogy would not be expected to account for the specific heat or thermal conductivity distributions within the flow. Using various coolant gases (air, carbon dioxide, nitrogen, and argon) and comparing with thermal experiments, the efficacy of the PSP method as a direct substitute for thermal measurements was evaluated on a cylindrical leading edge model with compound coolant injection. The results thus allow examination of how the two methods respond to different property variations. Overall, the PSP technique was found to overpredict the adiabatic effectiveness when compared to the results obtained from infrared (IR) thermography, but still reveals valuable information regarding the coolant flow.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Vol 123 (2) ◽  
pp. 231-237 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first-stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR=1.1 and 1.6 over a range of blowing conditions, 0.2⩽M⩽1.5 and 0.05⩽I⩽1.2. Two different mainstream turbulence intensity levels, Tu∞=0.5 and 20 percent, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50 deg injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M<0.5, there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

CFD Evaluations of Unconventional Film Cooling Scaling Parameters on a Simulated Turbine Blade Leading Edge

2014 ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Heat Capacity ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Density Effects ◽  
Number Ratio ◽  
Blade Leading Edge

While it is well understood that certain nondimensional parameters, such as freestream Reynolds number and turbulence intensity, must be matched for proper design of film cooling experiments, uncertainty continues on the ideal method to scale film cooling flow rate. This debate typically surrounds the influence of the coolant to freestream density ratio and whether mass flux ratio or momentum flux ratio properly accounts for the density effects. Unfortunately, density is not the only fluid property to differ between typical wind tunnel experiments and actual turbine conditions. Temperature differences account for the majority of the property differences; however, attempts to match density ratio through the use of alternative gases can exacerbate these property differences. A computational study was conducted to determine the influence of other fluid properties besides density — namely specific heat, thermal conductivity, and dynamic viscosity. CFD simulations were performed by altering traditional film cooling nondimensional parameters as well as others such as the Reynolds number ratio, Prandtl number ratio, and heat capacity ratio to evaluate their effects on adiabatic effectiveness and heat transfer coefficient. A cylindrical leading edge with a flat afterbody was used to simulate a turbine blade leading edge region. A single coolant hole was located 21.5° from the leading edge, angled 20° to the surface and 90° from the streamwise direction. Results indicated that thermal properties can play a significant role in understanding and matching results in cooling performance. Density effects certainly dominate; however, variations in conductivity and heat capacity can result in 10% or higher changes in the resulting heat flux to the surface when scaling ambient rig configurations to engine representative conditions.

Unsteady simulations of migration and deposition of fly-ash particles in the first-stage turbine of an aero-engine

2021 ◽  
pp. 1-21
Author(s):  
Z. Hao ◽  
X. Yang ◽  
Z. Feng
Keyword(s):  
Fly Ash ◽  
Film Cooling ◽  
Particle Deposition ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Velocity Model ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Aero Engine

Abstract Particulate deposits in aero-engine turbines change the profile of blades, increase the blade surface roughness and block internal cooling channels and film cooling holes, which generally leads to the degradation of aerodynamic and cooling performance. To reveal particle deposition effects in the turbine, unsteady simulations were performed by investigating the migration patterns and deposition characteristics of the particle contaminant in a one-stage, high-pressure turbine of an aero-engine. Two typical operating conditions of the aero-engine, i.e. high-temperature take-off and economic cruise, were discussed, and the effects of particle size on the migration and deposition of fly-ash particles were demonstrated. A critical velocity model was applied to predict particle deposition. Comparisons between the stator and rotor were made by presenting the concentration and trajectory of the particles and the resulting deposition patterns on the aerofoil surfaces. Results show that the migration and deposition of the particles in the stator passage is dominated by the flow characteristics of fluid and the property of particles. In the subsequential rotor passage, in addition to these factors, particles are also affected by the stator–rotor interaction and the interference between rotors. With higher inlet temperature and larger diameter of the particle, the quantity of deposits increases and the deposition is distributed mainly on the Pressure Side (PS) and the Leading Edge (LE) of the aerofoil.

Influence of Turbine Blade Leading Edge Profile on Film Cooling With Shaped Holes

2017 ◽  
Author(s):  
Mingjie Zhang ◽  
Nian Wang ◽  
Andrew F. Chen ◽  
Je-Chin Han
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Edge Profile ◽  
Elliptical Cylinders ◽  
Blade Leading Edge

This paper presents the turbine blade leading edge model film cooling effectiveness with shaped holes, using the pressure sensitive paint (PSP) mass transfer analogy method. The effects of leading edge profile, coolant to mainstream density ratio and blowing ratio are studied. Computational simulations are performed using the realizable k-ε turbulence model. Effectiveness obtained by CFD simulations are compared with experiments. Three leading edge profiles, including one semi-cylinder and two semi-elliptical cylinders with an after body, are investigated. The ratios of major to minor axis of two semi-elliptical cylinders are 1.5 and 2.0, respectively. The leading edge has three rows of shaped holes. For the semi-cylinder model, shaped holes are located at 0 degrees (stagnation line) and ± 30 degrees. Row spacing between cooling holes and the distance between impingement plate and stagnation line are the same for three leading edge models. The coolant to mainstream density ratio varies from 1.0 to 1.5 and 2.0, and the blowing ratio varies from 0.5 to 1.0 and 1.5. Mainstream Reynolds number is about 100,900 based on the diameter of the leading edge cylinder, and the mainstream turbulence intensity is about 7%. The results provide an understanding of the effects of leading edge profile and on turbine blade leading edge region film cooling with shaped-hole designs.

Experimental Study of the Effects of an Oscillating Approach Flow on Overall Cooling Performance of a Simulated Turbine Blade Leading Edge

2009 ◽  
Author(s):  
Ross Johnson ◽  
Jonathan Maikell ◽  
David Bogard ◽  
Justin Piggush ◽  
Atul Kohli ◽  
...  
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Stagnation Line ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Oscillation Frequencies ◽  
Overall Effectiveness ◽  
Blade Leading Edge

When a turbine blade passes through wakes from upstream vanes it is subjected to an oscillation of the direction of the approach flow resulting in the oscillation of the position of the stagnation line on the leading edge of the blade. In this study an experimental facility was developed that induced a similar oscillation of the stagnation line position on a simulated turbine blade leading edge. The overall effectiveness was evaluated at various blowing ratios and stagnation line oscillation frequencies. The location of the stagnation line on the leading edge was oscillated to simulate a change in angle of attack between α = ± 5° at a range of frequencies from 2 to 20 Hz. These frequencies were chosen based on matching a range of Strouhal numbers typically seen in an engine due to oscillations caused by passing wakes. The blowing ratio was varied between M = 1, M = 2, and M = 3. These experiments were carried out at a density ratio of DR = 1.5 and mainstream turbulence levels of Tu ≈ 6%. The leading edge model was made of high conductivity epoxy in order to match the Biot number of an actual engine airfoil. Results of these tests showed that the film cooling performance with an oscillating stagnation line was degraded by as much as 25% compared to the performance of a steady flow with the stagnation line aligned with the row of holes at the leading edge.

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