Effect of Self-Sustained Pulsation of Coolant Flow on Adiabatic Effectiveness and Net Heat Flux Reduction on a Flat Plate

2021 ◽  
Author(s):  
Nicola Rosafio ◽  
Simone Salvadori ◽  
Daniela Anna Misul ◽  
Mirko Baratta ◽  
Mauro Carnevale ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Field ◽  
Working Conditions ◽  
Film Cooling ◽  
Inlet Section ◽  
Complex Flow ◽  
Cooling Systems ◽  
Length Scales ◽  
Net Heat Flux ◽  
Adiabatic Effectiveness

Abstract Advanced film-cooling systems are necessary to guarantee safe working conditions of high-pressure turbine stages. A fair prediction of the inherent unsteady interaction between the main-flow and the jet of cooling air allows for correctly describing the complex flow structures arising close to the cooled region. This proves to be crucial for the design of high-performance cooling systems. Results obtained by means of an experimental campaign performed at the University of Karlsruhe are shown along with unsteady numerical data obtained for the corresponding working conditions. The experimental rig consists of an instrumented plate where the hot flow reaches Mach = 0.6 close to the coolant jet exit section. The numerical campaign models the unsteady film cooling characteristics using a third-order accurate method. The ANSYS® FLUENT® software is used along with a mesh refinement procedure that allows for accurately modelling the flow field. Turbulence is modelled using the k-ω SST model. Time-averaged and time-resolved distributions of adiabatic effectiveness and Net Heat Flux Reduction are analysed to determine to what extent deterministic unsteadiness plays a role in cooling systems. It is found that coolant pulsates due to fluctuations generated by flow separation at the inlet section of the cooling channel. Visualizations of the fluctuating flow field demonstrate that coolant penetration depends on the phase of the pulsation, thus leading to periodically reduced shielding. Eventually, unsteadiness occurring at integral length scales does not provide enough mixing to match the experiments, thus hinting that the dominant phenomena occur at inertial length scales.

Scaling of Adiabatic Effectiveness and Net Heat Flux Reduction From Near Ambient to Engine Temperatures

2015 ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
James L. Rutledge
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Thermal Boundary Layer ◽  
Thermal Condition ◽  
Adiabatic Wall ◽  
Ambient Temperatures ◽  
Wall Boundary Condition ◽  
Net Heat Flux ◽  
Adiabatic Effectiveness ◽  
Adiabatic Case

The present work computationally examines the scaling of a fan-shaped hole’s film-cooling performance from a near ambient temperature to an engine temperature on a flat plate. Heat flux distributions for both film-cooled and non-film-cooled cases were computed for several isothermal boundary conditions. Cases with engine representative freestream temperatures and near ambient temperatures were examined. This study first shows that the adiabatic wall temperatures interpolated from the isothermal results were lower than those measured directly using an adiabatic wall boundary condition. This was due to the presence of a thermal boundary layer in the isothermal results, which would not develop for the adiabatic case. As a result, the adiabatic effectiveness found with adiabatic models will not represent the true thermal condition found in the engine. Finally, this study shows that both the adiabatic effectiveness interpolated from the isothermal results and Net Heat Flux Reduction can be scaled from low temperature to high temperature by proper non-dimensional matching.

A Preliminary Numerical Study on the Effect of High Freestream Turbulence on Anti-Vortex Film Cooling Design at High Blowing Ratio

2010 ◽  
Author(s):  
Benson K. Hunley ◽  
Andrew C. Nix ◽  
James D. Heidmann
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Numerical Study ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Blowing Ratio ◽  
Net Heat Flux ◽  
Cooling Design ◽  
Adiabatic Effectiveness ◽  
Density Ratios

Researchers at NASA Glenn Research Center have developed and investigated a novel film cooling design, the anti-vortex hole (AVH), which has been shown to cancel or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low turbulence levels. This paper presents preliminary CFD results on the film effectiveness and net heat flux reduction at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. Baseline cases at low turbulence levels of 5% intensity and length scale of Λx/dm = 1 with a nominal blowing ratio of 2 and a density ratios of 1 and 2 were compared to previous results reported by Heidmann [1]. Higher freestream turbulence cases were investigated with a turbulence intensity and length scale of 10% and Λx/dm = 1 and 3, respectively. Results showed that higher freestream turbulence improves adiabatic effectiveness for the AVH design.

scholarly journals Highly Turbulent Mainstream Effects on Film Cooling of a Simulated Airfoil Leading Edge

1999 ◽  
Author(s):  
Christopher A. Johnston ◽  
David G. Bogard ◽  
Marcus A. McWaters
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Relative Increase ◽  
Stagnation Line ◽  
Net Heat Flux ◽  
Adiabatic Effectiveness

The influence of a high mainstream turbulence was examined in an experimental study of film cooling on a simulated turbine blade leading edge. Detailed heat transfer coefficient and adiabatic effectiveness values were measured under conditions representative of actual environments in a gas turbine engine. The two parameters were also combined for a net heat flux reduction analysis. Turbulence levels of Tu = 17% were achieved by modifying a cross-jets turbulence generator with a large cylinder element. A quarter cylinder geometry was used to simulate the turbine blade leading edge. Two staggered rows of nine holes each were incorporated with a geometry consistent with current industry design practices. One row was positioned nominally on the stagnation line, x/d = 0, while the other was located 25° from the stagnation line. The holes were spaced at S/d = 7.64 with a shallow injection angle of 20° and oriented at 90° to the streamwise direction. Comparisons were made to previous studies of heat transfer rates and adiabatic effectiveness values under low turbulence (Tu < 0.5%) conditions. Adiabatic effectiveness was generally decreased by about 20% due to the high mainstream turbulence, although a much greater decrease occurred at the stagnation line at lower blowing rates. The relative increase in heat transfer coefficient due the coolant injection was found to be significantly smaller for the high mainstream turbulence case compared to the low mainstream turbulence case. This was particularly important when evaluating the overall performance of this film cooling hole configuration, since the much smaller relative increase in heat transfer coefficient resulted in good performance in terms of net heat flux reduction.

scholarly journals Effect of Coolant Injection on Heat Transfer for a Simulated Turbine Airfoil Leading Edge

1998 ◽  
Author(s):  
Ushio M. Yuki ◽  
David G. Bogard ◽  
J. Michael Cutbirth
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Cooling ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Net Heat Flux ◽  
Overall Performance ◽  
Adiabatic Effectiveness

This paper presents an experimental study of the heat transfer on the leading edge of a simulated film cooled turbine airfoil. Previous studies have shown that use of film cooling on the leading edge of an airfoil can significantly increase the heat transfer coefficients around the leading edge which counter-acts the benefits of the adiabatic effectiveness provided by the coolant film. These heat transfer results complement our earlier study of the adiabatic effectiveness for this leading edge and film cooling hole geometry. Heat transfer and adiabatic effectiveness results were combined to determine the overall performance of the film cooling in terms of the net heat flux reduction. Heat transfer coefficients were found to be significantly increased by the film cooling flow in a narrow region which followed the path of the coolant flow. However, heat transfer coefficients were maximum to one side of the coolant jet, consistent with a streamwise vortex flow which is believed to be generated by the interaction of the mainstream with the coolant jet. Overall performance in terms of the net heat flux reduction was found to be unaffected by the large heat transfer coefficients in the vicinity of the holes, but was significantly diminished farther downstream.

A Novel Antivortex Turbine Film-Cooling Hole Concept

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
James D. Heidmann ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Circular Cross Section ◽  
Round Hole ◽  
Net Heat Flux ◽  
Cooling Hole ◽  
Film Cooling Holes

A novel turbine film-cooling hole shape has been conceived and designed at NASA Glenn Research Center. This “antivortex” design is unique in that it requires only easily machinable round holes, unlike shaped film-cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film-cooling holes. This vorticity typically entrains hot freestream gas and is associated with jet separation from the turbine blade surface. The antivortex film-cooling hole concept has been modeled computationally for a single row of 30 deg angled holes on a flat surface using the 3D Navier–Stokes solver GLENN-HT. A blowing ratio of 1.0 and density ratios of 1.05 and 2.0 are studied. Both film effectiveness and heat transfer coefficient values are computed and compared to standard round hole cases for the same blowing rates. A net heat flux reduction is also determined using both the film effectiveness and heat transfer coefficient values to ascertain the overall effectiveness of the concept. An improvement in film effectiveness of about 0.2 and in net heat flux reduction of about 0.2 is demonstrated for the antivortex concept compared to the standard round hole for both blowing ratios. Detailed flow visualization shows that as expected, the design counteracts the detrimental vorticity of the round hole flow, allowing it to remain attached to the surface.

Influence of Film Cooling Hole Angles and Geometries on Aerodynamic Loss and Net Heat Flux Reduction

2011 ◽  
Author(s):  
Chia Hui Lim ◽  
Graham Pullan ◽  
Peter Ireland
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Design Parameters ◽  
Aerodynamic Loss ◽  
Design Engineers ◽  
Net Heat Flux ◽  
Cooling Hole ◽  
Shaped Hole

Turbine design engineers have to ensure that film cooling can provide sufficient protection to turbine blades from the hot mainstream gas, while keeping the losses low. Film cooling hole design parameters include inclination angle (α), compound angle (β), hole inlet geometry and hole exit geometry. The influence of these parameters on aerodynamic loss and net heat flux reduction is investigated, with loss being the primary focus. Low-speed flat plate experiments have been conducted at momentum flux ratios of IR = 0.16, 0.64 and 1.44. The film cooling aerodynamic mixing loss, generated by the mixing of mainstream and coolant, can be quantified using a three-dimensional analytical model that has been previously reported by the authors. The model suggests that for the same flow conditions, the aerodynamic mixing loss is the same for holes with different α and β but with the same angle between the mainstream and coolant flow directions (angle κ). This relationship is assessed through experiments by testing two sets of cylindrical holes with different α and β: one set with κ = 35°, another set with κ = 60°. The data confirm the stated relationship between α, β, κ and the aerodynamic mixing loss. The results show that the designer should minimise κ to obtain the lowest loss, but maximise β to achieve the best heat transfer performance. A suggestion on improving the loss model is also given. Five different hole geometries (α = 35.0°, β = 0°) were also tested: cylindrical hole, trenched hole, fan-shaped hole, D-Fan and SD-Fan. The D-Fan and the SD-Fan have similar hole exits to the fan-shaped hole but their hole inlets are laterally expanded. The external mixing loss and the loss generated inside the hole are compared. It was found that the D-Fan and the SD-Fan have the lowest loss. This is attributed to their laterally expanded hole inlets, which lead to significant reduction in the loss generated inside the holes. As a result, the loss of these geometries is ≈ 50% of the loss of the fan-shaped hole at IR = 0.64 and 1.44.

Investigation of Steady and Unsteady Film-Cooling Using Immersed Mesh Blocks With New Conservative Interface Scheme

2016 ◽  
Author(s):  
Y. Jiang ◽  
L. He ◽  
L. Capone ◽  
E. Romero
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Computational Modelling ◽  
Length Scales ◽  
Cooling Flows ◽  
Cooling Flow ◽  
Mainstream Flow ◽  
Design Analyses ◽  
First Time ◽  
Advanced Development

Advanced development of high pressure turbines requires accurate predictions of film cooling flow. However, the length scales inherent to film cooling flows produce a large disparity compared to those of the mainstream flow field. To address this computational modelling challenge, an immersed mesh block (IMB) methodology has been initiated (Lad and He, 2011) which uses the much refined mesh around cooling holes to be mapped into the base mesh which tends to be much coarser for blade aerodynamic designs. Both the base mesh flow field and that of the IMB are solved simultaneously. By employing a simultaneous two-way coupling, the flow physics in and around cooling holes is able to interact with the mainstream, hence the length scales of both types of flow, as well as their interactions, are appropriately captured and resolved. The present work is aimed to develop a new numerical scheme for enforcing conservation at the interfacing boundary between the immersed cooling block and the base mesh, as well as, carry out a systematic validation and application of the IMB method for some well-established film-cooling experimental configurations (cylindrical and fan-shaped holes) at different blowing ratios. During the validation process, the mesh counts/resolution requirements for consistent cooling predictions for design analyses are established. The method is then applied to a transonic HPT stage. Its steady and unsteady flows are investigated. The results consistently demonstrate the effectiveness and applicability of the conservative IMB method, and indicate, for the first time, some interesting and relevant unsteady film-cooling behaviour.

Velocity and Turbulence Intensity Profiles Downstream of a Long Reach Endwall Double Row of Film Cooling Holes in a Gas Turbine Combustor Representative Environment

2015 ◽  
Author(s):  
Irene Cresci ◽  
Peter T. Ireland ◽  
Marko Bacic ◽  
Ian Tibbott ◽  
Anton Rawlinson
Keyword(s):  
Flow Field ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Momentum Flux ◽  
Diameter Ratio ◽  
Double Row ◽  
Length Scales ◽  
Cylindrical Holes ◽  
Endwall Film Cooling ◽  
Film Cooling Holes

The continuous demand from the airlines for reduced jet engine fuel consumption results in increasingly challenging high pressure turbine nozzle guide vane (NGV) working conditions. The capability to reproduce realistic boundary conditions in a rig at the combustor-turbine interaction plane is a key feature when testing NGVs in an engine-representative environment. A large scale linear cascade rig to investigate NGV leading edge cooling systems has been designed with particular attention being paid to creating engine representative conditions at the inlet to the NGVs. The combustor simulator replicates the main features of a rich-burn design including large dilution jets and extensive endwall film cooling. A three-dimensional computational domain including the entire combustor simulator has been created and RANS CFD simulations have been run in order to match Reynolds number and mainstream-to-coolant momentum flux ratio; velocity and turbulence measurements have been acquired at the NGV inlet plane at ambient temperature. In this engine-representative environment the authors focused their attention on the flow field downstream of different endwall film cooling holes configurations: three arrangements of a double row of staggered cylindrical holes (lateral pitch-to-diameter ratio of 2–3–6) and one with intersecting holes (intersecting angle of 90°) are experimentally and numerically analyzed. Velocity, turbulence intensity and integral length scales are predicted and measured for a density ratio of 1 and coolant-to-mainstream momentum flux of 6. A hot wire sensor was mounted on a two-axis traverse mechanism able to move the probe in the spanwise and lateral directions. Three slots allowed to reposition the traverse and take measurements at three downstream locations (stream-wise distance-to-diameter ratio of 4.2–9.2–14.2). The research confirmed the strong influence of the endwall coolant on the flow field at the NGV inlet plane and the hole spacing results a key parameter in managing the film development. Closer-spaced hole configurations can assure an effective film coverage. The integral length scales are strongly connected to the hole diameter and spacing. Intersecting holes can potentially reduce the amount of required coolant at a fixed pressure ratio, but they offer worst film performance than cylindrical holes. RANS simulations proved to be able to get the main trends shown by the measurements.

Visualization Experiment with PIV and Analysis of Flow Field in Hydrodynamic Coupling

2010 ◽  
Vol 29-32 ◽  
pp. 1327-1333
Author(s):  
Xiu Quan Lu ◽  
Wen Xing Ma ◽  
Li Dan Fan ◽  
Bo Sen Cai
Keyword(s):  
Flow Field ◽  
Working Conditions ◽  
Internal Flow ◽  
Two Dimensions ◽  
Flow State ◽  
Complex Flow ◽  
Piv Technique ◽  
Hydrodynamic Coupling ◽  
Visualization Experiment ◽  
Testing Technology

In order to study the complex flow state of the internal flow field while the hydrodynamic coupling is under working conditions, the two dimensions PIV technique of the modern testing technology is adopted to test and analyze typical working conditions of hydrodynamic coupling. According to the experimental results, the internal flow field of the typical working conditions is analyzed and compared in qualitative way. The research of this paper has guiding significance for the hydrodynamic coupling design.

Film Cooling From Short Holes With Sister Hole Influence

2012 ◽  
Author(s):  
Marc J. Ely ◽  
B. A. Jubran
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Film Cooling ◽  
Computational Analysis ◽  
Numerical Study ◽  
Vortical Flow ◽  
Injection Hole ◽  
Hole Configuration ◽  
Adiabatic Effectiveness ◽  
Structure Research

This paper reports a computational analysis on the effect of sister hole control on film cooling from short holes. The proposed method includes surrounding a primary injection hole by two or four smaller sister holes to actively maintain flow adhesion along the surface of the blade. A numerical study using the realizable k-ε turbulence model led to the determination that the use of sister holes significantly improves adiabatic effectiveness by countering the primary vortical flow structure. Research was carried out to determine the optimum hole configuration, arriving at the conclusion that placing sister holes slightly downstream of the primary injection hole improves the near-hole effectiveness, while placing sister holes slightly upstream of the primary hole improves downstream effectiveness. Similar results were found in evaluating both long and short hole geometries with a significantly less coherent flow field arising from the short hole. However, on the whole, the sister hole approach to film cooling was found to offer viable improvements over standard cooling regimes.

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