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.

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.

Implicit LES for Shaped-Hole Film Cooling Flow

2017 ◽  
Author(s):  
Todd A. Oliver ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Robert D. Moser ◽  
Gregory Laskowski
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Flow ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Mean Temperature ◽  
Cooling Hole ◽  
The Mean ◽  
Adiabatic Effectiveness

Results of a recent joint experimental and computational investigation of the flow through a plenum-fed 7-7-7 shaped film cooling hole are presented. In particular, we compare the measured adiabatic effectiveness and mean temperature against implicit large eddy simulation (iLES) for blowing ratio approximately 2, density ratio 1.6, and Reynolds number 6000. The results overall show reasonable agreement between the iLES and the experimental results for the adiabatic effectiveness and gross features of the mean temperature field. Notable discrepancies include the centerline adiabatic effectiveness near the hole, where the iLES under-predicts the measurements by Δη ≈ 0.05, and the near-wall temperature, where the simulation results show features not present in the measurements. After showing this comparison, the iLES results are used to examine features that were not measured in the experiments, including the in-hole flow and the dominant fluxes in the mean internal energy equation downstream of the hole. Key findings include that the flow near the entrance to the hole is highly turbulent and that there is a large region of backflow near the exit of the hole. Further, the well-known counter-rotating vortex pair downstream of the hole is observed. Finally, the typical gradient diffusion hypothesis for the Reynolds heat flux is evaluated and found to be incorrect.

Analysis of the Unsteady Flow Field Inside a Fan-Shaped Cooling Hole Predicted by Large-Eddy Simulation

2020 ◽  
Author(s):  
Shubham Agarwal ◽  
Laurent Gicquel ◽  
Florent Duchaine ◽  
Nicolas Odier ◽  
Jérôme Dombard
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Fourier Transforms ◽  
Thermal Environment ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Film Cooling Effectiveness ◽  
Mode Decomposition ◽  
Large Eddy ◽  
Cooling Hole

Abstract Film cooling is a common technique to manage turbine vane and blade thermal environment. Optimizing its cooling efficiency is furthermore an active research topic which goes in hand with a strong knowledge of the flow associated with a cooling hole. The following paper aims at developing deeper understanding of the flow physics associated with a standard cooling hole and helping guide future cooling optimization strategies. For this purpose, Large Eddy Simulations (LES) of the 7-7-7 fan-shaped cooling hole [1] is performed and the flow inside the cooling hole is studied and discussed. Use of mathematical techniques such as the Fast Fourier Transforms (FFT) and Dynamic Mode Decomposition (DMD) is done to quantitatively access the flow modal structure inside the hole based on the LES unsteady predictions. Using these techniques, distinct vortex features inside the cooling hole are captured. These features mainly coincide with the roll-up of the internal shear layer formed at the interface of the separation region at the hole inlet. The topology of these vortex features is discussed in detail and it is also shown how the expansion of the cross-section in case of shaped holes aids in breaking down these vortices. Indeed upon escaping, these large scale features are known to not be always beneficial to film cooling effectiveness.

Dynamic mode decomposition analysis of the flow characteristics in a centrifugal compressor with vaned diffuser

2020 ◽  
pp. 095765092091346
Author(s):  
Xiaojian Li ◽  
Yijia Zhao ◽  
Zhengxian Liu ◽  
Ming Zhao
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Dynamic Mode Decomposition ◽  
Flow Structures ◽  
Dynamic Mode ◽  
Tip Leakage ◽  
Mode Decomposition ◽  
Dynamic Structures

To understand the flow dynamic characteristics of a centrifugal compressor, the dynamic mode decomposition (DMD) method is introduced to decompose the complex three-dimensional flow field. Three operating conditions, peak efficiency (OP1), peak pressure ratio (OP2), and small mass flow rate (near stall, OP3) conditions, are analyzed. First, the physical interpretations of main dynamic modes at OP1 are identified. As a result, the dynamic structures captured by DMD method are closely associated with the flow characteristics. In detail, the BPF/2BPF (blade passing frequency) corresponds to the impeller–diffuser interaction, the rotor frequency (RF) represents the tip leakage flow (TLF) from leading edge, and the 4RF is related to the interaction among the downstream TLF, the secondary flow, and the wake vortex. Then, the evolution of the dynamic structures is discussed when the compressor mass flow rate consistently declines. In the impeller, the tip leakage vortex near leading edge gradually breaks down due to the high backpressure, resulting in multi-frequency vortices. The broken vortices further propagate downstream along streamwise direction and then interact with the flow structures of 4RF. As a result, the 8RF mode can be observed in the whole impeller, this mode is transformed from upstream RF and 4RF modes, respectively. On the other hand, the broken vortices show broadband peak spectrum, which is correlated to the stall inception. Therefore, the sudden boost of energy ratio of 14RF mode could be regarded as a type of earlier signal for compressor instability. In the diffuser, the flow structures are affected by the perturbation from the impeller. However, the flow in diffuser is more stable than that in impeller at OP1–OP3, since the leading modes are stable patterns of BPF/2BPF.

scholarly journals Experimental and Numerical Investigation of Sweeping Jet Film Cooling

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Mohammad A. Hossain ◽  
Robin Prenter ◽  
Ryan K. Lundgreen ◽  
Ali Ameri ◽  
James W. Gregory ◽  
...  
Keyword(s):  
Film Cooling ◽  
Thermal Field ◽  
Numerical Study ◽  
Convective Heat Transfer Coefficient ◽  
Density Ratio ◽  
Vortex Pair ◽  
Lateral Direction ◽  
Time Resolved ◽  
Jet In Crossflow ◽  
Cooling Hole

A companion experimental and numerical study was conducted for the performance of a row of five sweeping jet (SJ) film cooling holes consisting of conventional curved fluidic oscillators with an aspect ratio (AR) of unity and a hole spacing of P/D = 8.5. Adiabatic film effectiveness (η), thermal field (θ), convective heat transfer coefficient (h), and discharge coefficient (CD) were measured at two different freestream turbulence levels (Tu = 0.4% and 10.1%) and four blowing ratios (M = 0.98, 1.97, 2.94, and 3.96) at a density ratio of 1.04 and hole Reynolds number of ReD = 2800. Adiabatic film effectiveness and thermal field data were also acquired for a baseline 777-shaped hole. The SJ film cooling hole showed significant improvement in cooling effectiveness in the lateral direction due to the sweeping action of the fluidic oscillator. An unsteady Reynolds-averaged Navier–Stokes (URANS) simulation was performed to evaluate the flow field at the exit of the hole. Time-resolved flow fields revealed two alternating streamwise vortices at all blowing ratios. The sense of rotation of these alternating vortices is opposite to the traditional counter-rotating vortex pair (CRVP) found in a “jet in crossflow” and serves to spread the film coolant laterally.

Film Cooling of Cylindrical Hole With a Downstream Short Crescent-Shaped Block

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Baitao An ◽  
Jianjun Liu ◽  
Chao Zhang ◽  
Sijing Zhou
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cylindrical Hole ◽  
Test Case ◽  
Main Body ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper presents a method to improve the film-cooling effectiveness of cylindrical holes. A short crescent-shaped block is placed at the downstream of a cylindrical cooling hole. The block shape is defined by a number of geometric parameters including block height, length and width, etc. The single row hole on a flat plate with inclination angle of 30 deg, pitch ratio of 3, and length-diameter ratio of 6.25 was chosen as the baseline test case. Film-cooling effectiveness for the cylindrical hole with or without the downstream short crescent-shaped block was measured by using the pressure sensitive paint (PSP) technique. The density ratio of coolant (argon) to mainstream air is 1.38. The blowing ratios vary from 0.5 to 1.25. The results showed that the lateral averaged cooling effectiveness is increased remarkably when the downstream block is present. The downstream short block allows the main body of the coolant jet to pass over the block top and to form a new down-wash vortex pair, which increases the coolant spread in the lateral direction. The effects of each geometrical parameter of the block on the film-cooling effectiveness were studied in detail.

Effect of High Freestream Turbulence on Flowfields of Shaped Film Cooling Holes

2015 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Gas Turbine ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Lateral Spreading ◽  
Freestream Turbulence ◽  
Blowing Ratio ◽  
Turbine Airfoils ◽  
Film Cooling Holes

Shaped film cooling holes have become a standard geometry for protecting gas turbine components. Few studies, however, have reported flowfield measurements for moderately-expanded shaped holes and even fewer have reported on the effects of high freestream turbulence intensity relevant to gas turbine airfoils. This study presents detailed flowfield and adiabatic effectiveness measurements for a shaped hole at freestream turbulence intensities of 0.5% and 13%. Test conditions included blowing ratios of 1.5 and 3 at a density ratio of 1.5. Measured flowfields revealed a counter-rotating vortex pair and high jet penetration into the mainstream at the blowing ratio of 3. Elevated freestream turbulence had a minimal effect on mean velocities and rather acted by increasing turbulence intensity around the coolant jet, resulting in increased lateral spreading of coolant.

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