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.

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.

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.

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.

Experimental Validation of Quasisteady Assumption in Modeling of Unsteady Film-Cooling

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Stefan Bernsdorf ◽  
Martin G. Rose ◽  
Reza S. Abhari
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Three Dimensional ◽  
Flow Region ◽  
Pressure Side ◽  
Blowing Ratio ◽  
Jet Trajectory ◽  
Air Streams

This paper reports on the validation of the assumption of quasisteady behavior of pulsating cooling injection in the near hole flow region. The respective experimental data are taken in a flat plate wind tunnel at ETH Zürich. 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 a larger scale. Heating the free stream air and strongly cooling the coolant gives the required density ratio between coolant and free-stream. The coolant is injected with different frequency and amplitude. The three-dimensional velocities are recorded using nonintrusive PIV, and 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 general flow field, the jet trajectory, and the streamwise circulation are utilized in the validation of the quasisteady assumption.

Investigation of Various Parametric Influences on Leading Edge Film Cooling

1997 ◽  
Author(s):  
Michael W. Cruse ◽  
Ushio M. Yuki ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Line Position ◽  
Stagnation Line ◽  
Free Stream Turbulence ◽  
Adiabatic Effectiveness ◽  
Density Ratios

Film cooling adiabatic effectiveness of a simulated turbine airfoil leading edge was studied experimentally. The leading edge had two rows of holes, one at nominally the stagnation line position and the second a few hole diameters downstream. Hole positions at the leading edge, and inclination of the holes with respect to the surface, were different than typically used in previous studies, but were representative of current design practice. Various leading edge film cooling parameters were investigated including stagnation line position, free-stream turbulence level, leading edge geometry, and coolant to mainstream density ratio. Large density ratios were obtained by cooling the injected coolant to very low temperatures. Large scale, high level free-stream turbulence (Tu = 20%) was generated using a specially developed cross-jet turbulence generator. An infrared camera system was used to obtain well resolved surface temperature distributions around the coolant holes and across the leading edge. Results from the experiments showed considerably higher optimum blowing ratios than found in previous studies. The stagnation line position was found to be important in influencing the direction of coolant flow from the first row of holes. High free-stream turbulence levels were found to greatly decrease adiabatic effectiveness at low blowing ratios (M = 1.0), but had little effect at high blowing ratios (M = 2.0 and 2.5). Adiabatic effectiveness distributions were very similar for circular and elliptical leading edges. Experiments conducted at coolant to mainstream density ratios of 1.1 and 1.8 showed distinctly different flow characteristics in the stagnation line region for the different density ratio coolants.

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