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.

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.

Modal Analysis of Inclined Jet Film Cooling Flows With Density Variation

2013 ◽  
Author(s):  
Prasad Kalghatgi ◽  
Sumanta Acharya
Keyword(s):  
Modal Analysis ◽  
Wall Temperature ◽  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Intermediate Frequency ◽  
Hydrodynamic Flow ◽  
Dynamic Mode Decomposition ◽  
Flow Structures ◽  
Dynamic Mode

Thermal and hydrodynamic flow field over a flat surface cooled with a single round inclined film cooling jet and fed by a plenum chamber is numerically investigated using Large Eddy Simulation (LES) and validated with published measurements. The calculations are done for a free stream Reynolds number Re = 16000, density ratio of coolant to free stream fluid ρj/ρ∞ = 2.0 and blowing ratio BR = ρjV/ρ∞V = 1.0. A short delivery tube with aspect ratio l/D = 1.75 and 35° inclination is considered. The evolution of the Kelvin-Helmholtz (K-H), hairpin and Counter-Rotating Vortex Pair (CVP) vortical structures are discussed to identify their origins. Modal analysis of the complete 3D flow and temperature field is carried out using a Dynamic Mode Decomposition (DMD) technique. The modal frequencies are identified, and the specific modal contribution towards the cooling wall temperature fluctuation is estimated on the film cooling wall. The low and intermediate frequency modes associated with streamwise and hairpin flow structures are found to have largest contribution (in-excess of 28%) towards wall temperature (or cooling effectiveness) fluctuations. The high frequency Kelvin-Helmholtz mode contributes towards initial mixing in the region of film cooling hole away from the wall. The individual modal temperature fluctuations on the wall and their corresponding hydrodynamic flow structures are presented and discussed.

Internal Flow Structure of a Pressure-Swirl Atomizer at Two Different Density Ratios

2000 ◽  
Author(s):  
Dexin Wang ◽  
Zhanhua Ma ◽  
San-Mou Jeng ◽  
Michael A. Benjamin
Keyword(s):  
Reynolds Number ◽  
Flow Structure ◽  
Large Scale ◽  
Ambient Medium ◽  
Density Ratio ◽  
Internal Flow ◽  
Sudden Expansion ◽  
Working Fluid ◽  
Swirl Atomizer ◽  
Density Ratios

The flow fields of large-scale simplex nozzles were investigated by 2-D back-scattered Laser Doppler Velocimetry (LDV). The internal flow structures of a simplex nozzle at two different density ratios of the working fluid and the ambient medium were obtained. The effects of the density ratio, Reynolds Number and orifice geometry on the flow structure were examined. The results revealed that the density ratio only affects the internal flow field in the region where the radius is smaller than the orifice radius. The density ratio and Reynolds Number have stronger influence on the internal flow structure of a sudden contraction and 45° expansion orifice configuration than on that of a 45° contraction and sudden expansion orifice configuration. When the density ratio is one, the effect of the contraction geometry from swirl chamber to orifice on the internal flow is very small compared to the effect of the expansion geometry.

Experimental Flow Structure Investigation of Compound Angled Film Cooling

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Vipluv Aga ◽  
Martin Rose ◽  
Reza S. Abhari
Keyword(s):  
Flat Plate ◽  
Flow Structure ◽  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Cooling Flow ◽  
Blowing Ratio ◽  
Single Compound

The experimental investigation of film-cooling flow structure provides reliable data for calibrating and validating a 3D feature based computational fluid dynamics (CFD) model being developed synchronously at the ETH Zurich. This paper reports on the flow structure of a film-cooling jet emanating from one hole in a row of holes angled 20 deg to the surface of a flat plate having a 45 deg lateral angle to the freestream flow in a steady flow, flat plate wind tunnel. This facility simulates a film-cooling row typically found on a turbine blade, giving engine representative nondimensionals in terms of geometry and operating conditions. The main flow is heated and the injected coolant is cooled strongly to obtain the requisite density ratio. All three velocity components were measured using a nonintrusive stereoscopic particle image velocimetry (PIV) system. The blowing ratio and density ratio are varied for a single compound angled geometry, and the complex three dimensional flow is investigated with special regard to vortical structure.

Velocity Measurements Around Film Cooling Holes With Deposition

2010 ◽  
Author(s):  
Kristian Haase ◽  
Jeffrey P. Bons
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flat Plate ◽  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Flow Structures ◽  
Particle Image Velocimetry Technique ◽  
Film Cooling Holes

The choice of synthetic fuels (synfuels) in order to achieve greater fuel flexibility may lead to unwanted solid depositions on the blades of turbomachines. The objective of this paper is to gain information of the flow field over a turbine blade with depositions around the film cooling holes. For the investigation the particle image velocimetry technique (PIV) is utilized. The experiments are conducted in a low speed wind tunnel at a Reynolds number of 300,000 based on the distance from the leading edge to the middle of the cooling holes and a Reynolds number of 9,200 based on the hole diameter. Three different simulation plates are tested in the tunnel—a flat plate for comparison, a plate with large depositions only upstream of the holes, and one with smaller depositions all around the holes. The two deposition configurations are scaled models of actual depositions formed at simulated engine flow conditions on a turbine test coupon. The experiments are conducted at four different coolant to free stream blowing ratios—0, 0.5, 1, and 2—and at a density ratio of 1.1. PIV images are taken in four planes from the side of the tunnel to record the main flow structures and in five planes from the end of the tunnel to record the secondary flow structures. The results show that the type of deposition has a large influence on the flow field. With the smaller depositions the penetration of the coolant jet into the free stream is significantly reduced but the dimension and strength of the kidney vortices is increased compared to the flat plate. With the large depositions, on the other hand, the penetration of the coolant jet is much higher due to the ramp effect and the dimension of the secondary vortices is also increased. It can also be seen that the coolant gathers and stays behind the large depositions and then flows off very slowly. Film effectiveness and surface heat flux data acquired with the same plates (and reported previously) allow the identification of flow features and their direct influence on the film cooling performance.

Experimental and Numerical Investigation of Turbulent Mixing in Film Cooling Applications

2017 ◽  
Author(s):  
Michael Straußwald ◽  
Karin Schmid ◽  
Hagen Müller ◽  
Michael Pfitzner
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Density Ratio ◽  
Turbulent Heat Flux ◽  
Heat Fluxes ◽  
Flow Dynamics ◽  
Frame Rate ◽  
Experimental Investigations ◽  
Turbulent Heat ◽  
Future Design

Fundamental knowledge on the flow dynamics and in particular the turbulent heat flux in film cooling flows is essential for the future design process of efficient cooling geometries. Thermographic PIV has been used to measure temperature and velocity fields in flows emanating from cylindrical effusion holes simultaneously. The measurements were carried out in a closed-loop, heated wind tunnel facility at a repetition rate of 6 kHz. Due to the high frame rate of the measurements, the unsteady flow dynamics could be resolved. For a density ratio of DR = 1.6 and a momentum ratio of I = 8, the jet ejected from the cylindrical effusion hole lifts off the surface. From the instantaneous measurements it could be observed that pockets of hot air are entrained into the coolant forcing the relatively fast cooling air to dodge the slow main flow air. These shear layer fluctuations result in turbulent heat fluxes that do not follow the gradient diffusion hypothesis which is often used in RANS models. In addition to these experimental investigations, numerical results from RANS simulations with the k-ω-SST turbulence model are presented that were carried out as basis for future investigations on turbulent heat flux modeling.

Modeling of Film Cooling—Part I: Experimental Study of Flow Structure

2005 ◽  
Vol 128 (1) ◽  
pp. 141-149 ◽  
Author(s):  
Stefan Bernsdorf ◽  
Martin G. Rose ◽  
Reza S. Abhari
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Flow Structures ◽  
Pressure Side ◽  
Three Dimensional Flow ◽  
Blowing Ratio ◽  
Air Streams ◽  
Cooling Part ◽  
Cooling Model

This paper, which is Part I of a two part paper, reports on experimental data taken in a steady flow, flat plate wind tunnel at ETH Zürich, while Part II utilizes this data for calibration and validation purpose of a film cooling model embedded in a 3D CFD code. The facility simulates the film cooling row flow field on the pressure side of a turbine blade. Engine representative nondimensionals are achieved, providing a faithful model at larger scale. Heating the freestream air and strongly cooling the coolant gives the required density ratio between coolant and freestream. The three dimensional velocities are recorded using nonintrusive PIV; seeding is provided for both air streams. Two different cylindrical hole geometries are studied, with different angles. Blowing ratio is varied over a range to simulate pressure side film cooling. The three dimensional flow structures are revealed.

Modal Analysis of Inclined Film Cooling Jet Flow

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Prasad Kalghatgi ◽  
Sumanta Acharya
Keyword(s):  
Modal Analysis ◽  
Wall Temperature ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Intermediate Frequency ◽  
Hydrodynamic Flow ◽  
Dynamic Mode Decomposition ◽  
Flow Structures ◽  
Dynamic Mode

Thermal and hydrodynamic flow field over a flat surface cooled with a single round inclined film cooling jet and fed by a plenum chamber is numerically investigated using large eddy simulation (LES) and validated with published measurements. The calculations are done for a freestream Reynolds number Re = 16,000, density ratio of coolant to freestream fluid ρj/ρ∞=2.0, and blowing ratio BR=ρjV/ρ∞V=1.0. A short delivery tube with aspect ratio l/D=1.75 and 35 deg inclination is considered. The evolution of the Kelvin–Helmholtz (K-H), hairpin and counterrotating vortex pair (CVP) vortical structures are discussed to identify their origins. Modal analysis of the complete 3D flow and temperature field is carried out using a dynamic mode decomposition (DMD) technique. The modal frequencies are identified, and the specific modal contribution toward the cooling wall temperature fluctuation is estimated on the film cooling wall. The low and intermediate frequency modes associated with streamwise and hairpin flow structures are found to have the largest contribution (in-excess of 28%) toward the wall temperature (or cooling effectiveness) fluctuations. The high frequency Kelvin–Helmholtz mode contributes toward initial mixing in the region of film cooling hole away from the wall. The individual modal temperature fluctuations on the wall and their corresponding hydrodynamic flow structures are presented and discussed.

Numerical Investigation of Film Cooling Performance With Different Internal Flow Structures

2014 ◽  
Author(s):  
Jianxia Luo ◽  
Cunliang Liu ◽  
Huiren Zhu
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Internal Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Cooling Performance ◽  
Smooth Case ◽  
Air Jet ◽  
Smooth Channel ◽  
Cooling Hole

Four coolant channel configurations, including supply plenum without crossflow, smooth channel with crossflow and ribbed channels with crossflow ( 135° and 45° angled ribs), are simulated to find out the effect of internal flow structures on the external film cooling performance. Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. Blowing ratios cover a range from 0.5 to 2.0. For the three cases with crossflow, a constant Reynolds number, ReDh, is fixed as 100000. Particular attention has been paid to the flow structures and counter-rotating vortices. Helical motion of secondary flow is observed in the hole of the smooth case and the 45° ribs case, inducing strong velocity separation in the cooling hole and blocks at the entrance and exit. In the two cases, the cooling-air jet divides into two parts after being blown out of the hole and a pair of skewed vortices appears downstream. In the 135° ribs case, the vortex in the upper half region of the secondary flow channel rotates in the same direction with the hole inclination direction, the straight stream lines are generated and therefore lower loss and higher discharge coefficient. Experimental data of the smooth case and the 135° ribs case show the good agreement with the numerical results.

A Near-Field Investigation Into the Effects of Geometry and Compound Angle on the Flowfield of a Row of Film Cooling Holes

1998 ◽  
Author(s):  
Phillip A. Berger ◽  
James A. Liburdy
Keyword(s):  
Flow Structure ◽  
Film Cooling ◽  
Near Field ◽  
Density Ratio ◽  
Vortex Pair ◽  
Field Measurements ◽  
Field Investigation ◽  
Cross Sectional ◽  
Mainstream Flow ◽  
Compound Angle

The goal of this study was to determine the effects that hole geometry and compound angle have on the near-field downstream from a row of jets injected into a crossflow. Velocity and vorticity fields are presented in cross-sectional planes oriented perpendicular to the mainstream flow. Instantaneous field measurements were obtained using particle image velocimetry (PIV). Data were recorded at locations of 0, 1, 2, and 3.5 hole diameters downstream of injection for three different hole geometries inclined at 35° to the mainstream flow. These geometries consisted of a cylindrical hole, a 12° laterally-diffused hole, and a 15° forward-expanded hole with compound angles of 0°, 45°, 60°, and 90. Data are presented for a blowing ratio of 1.25 and density ratio of 1. The influences on jet penetration, coverage width, flow structure elevation, and flow structure separation for each configuration are discussed. Vorticity is presented in terms of field distribution and peak magnitudes. These studies show the degradation of the counter-rotating vortex pair into a singular, recirculating structure as the compound angle increases. Peak levels of vorticity are not encountered until between one and two diameters downstream of injection.

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