Unsteady Analysis of Adiabatic Film Cooling Effectiveness Behind a Row of Circular Holes Fed by Internal Crossflow

2019 ◽  
Author(s):  
Mohamed Qenawy ◽  
Wenwu Zhou ◽  
Han Chen ◽  
Hongyi Shao ◽  
Di Peng ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Film Cooling ◽  
Large Scale ◽  
Density Ratio ◽  
Main Role ◽  
Test Model ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Entry Length ◽  
Circular Holes

Abstract The adiabatic film cooling effectiveness behind a single row of circular holes fed by internal crossflow was measured by fast-response pressure-sensitive paint technique. During the experiment, the coolant flow was discharged from the coolant holes via either plenum or crossflow channel. The test model has a row of circular holes with 3D spacing, 6.5D entry length, and 35° inclination angle. Two blowing ratios (M = 0.40 and 0.80) were tested with a density ratio of 0.97. A numerical steady-state RANS simulation, using SST k-ω and Realizable k-ε turbulence models, was conducted to understand the internal crossflow behaviors. The unsteadiness caused by the flow structures (counter-rotating vortex pair (CRVP) and horseshoe vortex) was quantified by the root mean square and the cross-correlations. In addition, the proper orthogonal decomposition was used to identify the large-scale unsteady coherent structures and their contributions. The fluctuations of the crossflow feed were asymmetric, which were significantly weaker compared with the plenum case. The CRVP, as the most significant coherent structures, were demonstrated to play the main role in the unsteadiness of the crossflow feed.

Flow Structures and Unsteady Behaviors of Film Cooling from Discrete Holes Fed by Internal Crossflow

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Mohamed Qenawy ◽  
Han Chen ◽  
Di Peng ◽  
Yingzheng Liu ◽  
Wenwu Zhou
Keyword(s):  
Flow Structure ◽  
Film Cooling ◽  
Density Ratio ◽  
Internal Flow ◽  
Frame Rate ◽  
Flow Structures ◽  
Incline Angle ◽  
Main Role ◽  
Entry Length ◽  
Circular Holes

Abstract The flow structures and unsteady behaviors of a flat plate film cooling flow behind a single row of circular holes fed by internal crossflow were extensively investigated. The investigation was achieved experimentally using fast-response pressure-sensitive paint (PSP) at a high frame rate and numerically using large-eddy simulation (LES). During the experiment, the coolant flow was discharged from discrete holes (i.e., a row of circular holes with 3D spacing, 6.5D entry length, and 35 deg incline angle) via a crossflow channel. Two blowing ratios (M = 0.4 and 0.8) were tested at a density ratio of DR = 0.97. The measured unsteadiness caused by the predicted flow structure over the coolant surface was identified by spatial correlation. The unsteady signatures were decomposed and demonstrated by proper orthogonal decomposition (POD). The results reveal that the flow structure plays the main role in cooling performance and its instability. The internal flow produced a vortex tube structure that was responsible for the shear vortex (i.e., Kelvin–Helmholtz instabilities) between the coolant and the mainstream at the hole exit. The internal crossflow forced the legs of the counter-rotating vortex pair (CRVP) to spread laterally, and the coolant to fluctuate asymmetrically around the discrete holes. This unsteady behavior may potentially cause high thermal stress and leads to blade cracking over a long time.

scholarly journals Design and Evaluation of a Single Passage Test Model to Obtain Turbine Airfoil Film Cooling Effectiveness Data

1995 ◽  
Author(s):  
Frederick A. Buck ◽  
Chander Prakash
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Density Ratio ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Suction Side ◽  
Test Model ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Passage

A single passage test model has been designed to simulate the mainstream aerodynamics between two adjacent turbine airfoils and to measure the film cooling effectiveness from coolant injection on the pressure and suction sides of the airfoils. Film cooling tests were run on the model using a gas concentration/mass transfer technique with a foreign gas as the coolant to match density ratio. Aspects of the design and test are discussed including the use of a two-dimensional inviscid flow analysis to design boundary layer bleeds upstream of the pressure- and suction-side airfoil surfaces. Results of two- and three-dimensional viscous flow analyses that were used to evaluate various design features including inlet bellmouth, boundary layer bleeds, adjustable tailboards and model backpressure are presented. Aerodynamic and film cooling effectiveness test measurements made with the model will show that the model flow field can be controlled to match results from a previous thermal cascade test.

Effect of Showerhead Injection on Superposition of Multi-Row Pressure Side Film Cooling With Fan Shaped Holes

2003 ◽  
Author(s):  
Martin Schneider ◽  
Sacha Parneix ◽  
Jens von Wolfersdorf
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Density Ratio ◽  
Test Facility ◽  
Main Stream ◽  
Test Model ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row

In the present study the effect of approach boundary layer conditions on film cooling effectiveness superposition for pressure side fan shaped holes on a first stage vane is investigated. More particularly, the effect of showerhead cooling on the film effectiveness of downstream pressure side rows is addressed. The experimental test facility used is a continuously running , two passage, linear cascade wind tunnel equipped with a central vane and contoured side walls. Main stream stagnation conditions and pressure measurements on the vane external surface were taken to determine the isentropic Mach number distribution. The turbulence level generated with a bar grid is around 15%. Film cooling effectiveness has been determined with the narrow banded thermochromic liquid crystal steady state technique. Mainstream as well as coolant flow could be heated to shift the iso-temperature contours across the vane. Carbon dioxide was used as coolant gas to better match the density ratio in the experimental facility to engine conditions. The test model is a research vane equipped with four rows of cylindrical holes showerhead and three rows of fan shaped holes along the pressure side at typical inclination angles to the surface. The study incorporates single row blowing with the following row approach conditions: 1) no showerhead injection, 2) boundary layer trip, 3) isothermal showerhead blowing, and multi-row blowing with and without showerhead blowing. The results are used to investigate the applicability of the single row results superposition approach for multiple-row injection. Simulating the appropriate aerodynamic conditions during individual row measurements improves the superposition prediction in comparison to the multi-row results.

Conjugate Heat Transfer and Film Cooling of a Multi-Stage Cooling Scheme

2008 ◽  
Author(s):  
M. Ghorab ◽  
S. I. Kim ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Conjugate Heat Transfer ◽  
Density Ratio ◽  
Design Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Multi Stage ◽  
Internal Gap

Cooling techniques play a key role in improving efficiency and power output of modern gas turbines. The conjugate technique of film and impingement cooling schemes is considered in this study. The Multi-Stage Cooling Scheme (MSCS) involves coolant passing from inside to outside turbine blade through two stages. The first stage; the coolant passes through first hole to internal gap where the impinging jet cools the external layer of the blade. Finally, the coolant passes through the internal gap to the second hole which has specific designed geometry for external film cooling. The effect of design parameters, such as, offset distance between two-stage holes, gap height, and inclination angle of the first hole, on upstream conjugate heat transfer rate and downstream film cooling effectiveness performance are investigated computationally. An Inconel 617 alloy with variable properties is selected for the solid material. The conjugate heat transfer and film cooling characteristics of MSCS are analyzed across blowing ratios of Br = 1 and 2 for density ratio, 2. This study presents upstream wall temperature distributions due to conjugate heat transfer for different gap design parameters. The maximum film cooling effectiveness with upstream conjugate heat transfer is less than adiabatic film cooling effectiveness by 24–34%. However, the full coverage of cooling effectiveness in spanwise direction can be obtained using internal cooling with conjugate heat transfer, whereas adiabatic film cooling effectiveness has narrow distribution.

Assessment of a Double Hole Film Cooling Geometry Using S-PIV and PSP

2013 ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Charles P. Brown ◽  
Weston V. Harmon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Field Measurements ◽  
Secondary Flows ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Hole Geometry ◽  
Compound Angle

A novel, double hole film cooling configuration is investigated as an alternative to traditional cylindrical and fanshaped, laidback holes. This experimental investigation utilizes a Stereo-Particle Image Velocimetry (S-PIV) to quantitatively assess the ability of the proposed, double hole geometry to weaken or mitigate the counter-rotating vortices formed within the jet structure. The three-dimensional flow field measurements are combined with surface film cooling effectiveness measurements obtained using Pressure Sensitive Paint (PSP). The double hole geometry consists of two compound angle holes. The inclination of each hole is θ = 35°, and the compound angle of the holes is β = ± 45° (with the holes angled toward one another). The simple angle cylindrical and shaped holes both have an inclination angle of θ = 35°. The blowing ratio is varied from M = 0.5 to 1.5 for all three film cooling geometries while the density ratio is maintained at DR = 1.0. Time averaged velocity distributions are obtained for both the mainstream and coolant flows at five streamwise planes across the fluid domain (x/d = −4, 0, 1, 5, and 10). These transverse velocity distributions are combined with the detailed film cooling effectiveness distributions on the surface to evaluate the proposed double hole configuration (compared to the traditional hole designs). The fanshaped, laidback geometry effectively reduces the strength of the kidney-shaped vortices within the structure of the jet (over the entire range of blowing ratios considered). The three-dimensional velocity field measurements indicate the secondary flows formed from the double hole geometry strengthen in the plane perpendicular to the mainstream flow. At the exit of the double hole geometry, the streamwise momentum of the jets is reduced (compared to the single, cylindrical hole), and the geometry offers improved film cooling coverage. However, moving downstream in the steamwise direction, the two jets form a single jet, and the counter-rotating vortices are comparable to those formed within the jet from a single, cylindrical hole. These strong secondary flows lift the coolant off the surface, and the film cooling coverage offered by the double hole geometry is reduced.

Influence of Coolant Density on Turbine Platform Film-Cooling With Stator–Rotor Purge Flow and Compound-Angle Holes

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Kevin Liu ◽  
Shang-Feng Yang ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Fundamental Parameters ◽  
Blowing Ratio ◽  
Purge Flow ◽  
Cylindrical Holes ◽  
Exit Mach Number ◽  
Compound Angle

A detailed parametric study of film-cooling effectiveness was carried out on a turbine blade platform. The platform was cooled by purge flow from a simulated stator–rotor seal combined with discrete hole film-cooling. The cylindrical holes and laidback fan-shaped holes were accessed in terms of film-cooling effectiveness. This paper focuses on the effect of coolant-to-mainstream density ratio on platform film-cooling (DR = 1 to 2). Other fundamental parameters were also examined in this study—a fixed purge flow of 0.5%, three discrete-hole film-cooling blowing ratios between 1.0 and 2.0, and two freestream turbulence intensities of 4.2% and 10.5%. Experiments were done in a five-blade linear cascade with inlet and exit Mach number of 0.27 and 0.44, respectively. Reynolds number of the mainstream flow was 750,000 and was based on the exit velocity and chord length of the blade. The measurement technique adopted was the conduction-free pressure sensitive paint (PSP) technique. Results indicated that with the same density ratio, shaped holes present higher film-cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The optimum blowing ratio of 1.5 exists for the cylindrical holes, whereas the effectiveness for the shaped holes increases with an increase of blowing ratio. Results also indicate that the platform film-cooling effectiveness increases with density ratio but decreases with turbulence intensity.

Numerical Investigation of Effects of Blockage, Inclination Angle, and Hole-Size on Film Cooling Effectiveness at Concave Surface

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Fu-qiang Wang ◽  
Jian Pu ◽  
Jian-hua Wang ◽  
Wei-dong Xia
Keyword(s):  
Film Cooling ◽  
Pressure Loss ◽  
Numerical Study ◽  
Density Ratio ◽  
Concave Surface ◽  
Blockage Ratio ◽  
Coverage Area ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle

Abstract Film-hole can be often blocked by thermal-barrier coatings (TBCs) spraying, resulting in the variations of aerodynamic and thermal performances of film cooling. In this study, a numerical study of the blockage effect on the film cooling effectiveness of inclined cylindrical-holes was carried out on a concave surface to simulate the airfoil pressure side. Three typical blowing ratios (BRs) of 0.5, 1.0, and 1.5 were chosen at an engine-similar density ratio (DR) of 2.0. Two common inclination angles of 30 deg and 45 deg were designed. The blockage ratios were adjusted from 0 to 20%. The results indicated the blockage could enhance the penetration of film cooling flow to the mainstream. Thus, the averaged effectiveness and coolant coverage area were reduced. Moreover, the pressure loss inside of the hole was increased. With the increase of BR, the decrement of film cooling effectiveness caused by blockage rapidly increased. At BR = 1.5, the decrement could be acquired up to 70% for a blockage ratio of 20%. The decrement of film cooling effectiveness caused by blockage was nearly nonsensitive to the injection angle; however, the larger angle could generate the higher increment of pressure loss caused by blockage. A new design method for the couple scheme of film cooling and TBC was proposed, i.e., increasing the inlet diameter according to the blockage ratio before TBC spraying. In comparison with the original unblocked-hole, the enlarged blocked-hole not only kept the nearly same area-averaged effectiveness but also reduced slightly the pressure loss inside of the hole. Unfortunately, application of enlarged blocked-hole at large BR could lead to a more obvious reduction of effectiveness near hole-exit, in comparison with the original common-hole.

scholarly journals Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

2004 ◽  
Vol 10 (5) ◽  
pp. 345-354 ◽  
Author(s):  
Jan Dittmar ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Guide Vane ◽  
Inlet Temperature ◽  
Test Model ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

The demand of improved thermal efficiency and high power output of modern gas turbine engines leads to extremely high turbine inlet temperature and pressure ratios. Sophisticated cooling schemes including film cooling are widely used to protect the vanes and blades of the first stages from failure and to achieve high component lifetimes. In film cooling applications, injection from discrete holes is commonly used to generate a coolant film on the blade's surface.In the present experimental study, the film cooling performance in terms of the adiabatic film cooling effectiveness and the heat transfer coefficient of two different injection configurations are investigated. Measurements have been made using a single row of fanshaped holes and a double row of cylindrical holes in staggered arrangement. A scaled test model was designed in order to simulate a realistic distribution of Reynolds number and acceleration parameter along the pressure side surface of an actual turbine guide vane. An infrared thermography measurement system is used to determine highly resolved distribution of the models surface temperature. Anin-situcalibration procedure is applied using single embedded thermocouples inside the measuring plate in order to acquire accurate local temperature data.All holes are inclined 35° with respect to the model's surface and are oriented in a streamwise direction with no compound angle applied. During the measurements, the influence of blowing ratio and mainstream turbulence level on the adiabatic film cooling effectiveness and heat transfer coefficient is investigated for both of the injection configurations.

Turbine Vane Endwall Film Cooling From Cross-Row Configuration With Simulated Upstream Leakage Flow

2017 ◽  
Author(s):  
Nafiz H. K. Chowdhury ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Companion Paper ◽  
Leakage Flow ◽  
Blow Down ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Lift Off ◽  
Endwall Cooling

The performance of a full coverage film cooling configuration called cross-row (CR) configuration including upstream inlet leakage flow was studied by measuring the adiabatic film cooling effectiveness distribution using PSP technique. Experiments were conducted in a blow-down wind tunnel cascade facility at the isentropic exit Mach number of 0.5 corresponding to inlet Reynolds number of 3.8 × 105, based on axial chord length. A free-stream turbulence level was generated as high as 19% with a length scale of 1.7 cm at the inlet. The results are presented as two-dimensional adiabatic film cooling effectiveness distributions on the endwall surface with corresponding spanwise averaged distributions. The focus of this study is to investigate the effect of coolant-to-mainstream mass flow ratio (MFR) and density ratio (DR) on the proposed endwall cooling design. Initially, increased MFR for the endwall cooling and upstream leakage levels up the local adiabatic cooling effectiveness and yields relatively uniform coverage on the entire endwall. However, in either case, highest MFR does not provide any improvement as endwall cooling suffered from the jet lift-off and leakage coolant coverage restricted by the downstream near-wall flow field. Results also indicated a density ratio of 1.5 provides the best performance. Finally, a fair comparison is made with another design called axial-row (AR) configuration from a companion paper.

High Resolution Measurements of Local Effectiveness by Discrete Hole Film Cooling

1999 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Surface Temperature ◽  
Film Cooling ◽  
Density Ratio ◽  
Geometrical Parameters ◽  
Element Analysis ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flow Parameters ◽  
Wide Range ◽  
Local Measurements

Local adiabatic film cooling effectiveness on a flat plate surface downstream a row of cylindrical holes was investigated. Geometrical parameters like blowing angle and hole pitch as well as the flow parameters blowing rate and density ratio were varied in a wide range emphasizing on engine relevant conditions. An IR-thermography technique was used to perform local measurements of the surface temperature field. A spatial resolution of up to 7 data points per hole diameter extending up to 80 hole diameters downstream of the ejection location was achieved. Since all technical surface materials have a finite thermoconductivity, no ideal adiabatic conditions could be established. Therefore, a procedure for correcting the measured surface temperature data based on a Finite Element analysis was developed. Heat loss over the backside of the testplate and remnant heat flux within the testplate in lateral and streamwise direction were taken into account. The local effectiveness patterns obtained are systematically analyzed to quantify the influence of the various parameters. As a result, a detailed description of the characteristics of local adiabatic film cooling effectiveness is given. Furthermore, the locally resolved experimental results can serve as a data base for the validation of CFD-codes predicting discrete hole film cooling.

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