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Principles Of Enhanced Heat Transfer

CAA broadband noise prediction for aeroacoustic design

This paper presents the results of a detailed hydrodynamic study of a row of inclined jets issuing into a crossflow with a density ratio of injectant to freestream of two. Laser Doppler anemometry was used to measure the vertical and streamwise components of velocity for a jet-to-freestream mass flux ratio of 0.5. Mean velocity components and turbulent Reynolds normal and shear stress components were measured at locations in a vertical plane along the centerline of the jet from 1 diameter upstream to 30 diameters downstream of the jet. The results, which have application to film cooling, give a quantitative picture of the entire flow field, from the approaching flow upstream of the jet, through the interaction region of the jet and freestream, to the relaxation region downstream where the flow field approaches that of a standard turbulent boundary layer.Copyright © 1989 by ASME

Effects of density ratio on the hydrodynamics of film cooling

Large-eddy simulation of film cooling flows at density gradients

A review of gas turbine effusion cooling studies

The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling. A cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re ∞  = 400,000. This jet-in-a-crossflow (JICF) problem is investigated using large-eddy simulations (LES). The governing equations comprise the Navier–Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture. A variation of the density ratio is simulated by the heat-mass transfer analogy, i.e., gases of different density are effused into an air crossflow at a constant temperature. An efficient large-eddy simulation method for low subsonic flows based on an implicit dual time-stepping scheme combined with low Mach number preconditioning is applied. The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement. The results show the dynamics of the flow field in the vicinity of the jet hole, i.e., the recirculation region and the inclination of the shear layers, to be mainly determined by the velocity ratio. However, evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter, i.e., the density ratio between the fluids and the velocity ratio have to be considered.

Large-eddy Simulation of Film Cooling Flows with Variable Density Jets

Noise prediction for a turbulent jet using different hybrid methods

In the present paper the flow field of a film cooling configuration with cylindrical holes embedded in a shallow cavity is investigated using large-eddy simulation (LES). The cooling jet is injected through a single row of inclined holes from a transverse cavity into a turbulent flat plate boundary layer at a temperature ratio of TR = 0.44 . The mixing of the cooling fluid and the crossflow within the cavity is a highly unsteady process generating complex vortical structures. The impact of the boundary layer separation at the upstream cavity edge on the jet-crossflow interaction is studied in detail. The driving mechanisms of the momentum and heat exchange between the jet and the crossflow are identified and discussed. The flow field and the adiabatic cooling efficiency is compared to a standard cylindrical film cooling configuration without a cavity. The development of the counter-rotating vortex pair (CVP) downstream of the jet injection is investigated. An analysis of the vortex dynamics shows an impinging behavior of the jet fluid in this area. The Reynolds stress shows a more two-dimensional distribution compared to the anisotropic nature of the jet-in-a-crossflow (JICF) at standard cylindrical holes. Since the heat exchange is closely connected to the transport of momentum in the mixed boundary layer, this observation explains the enhanced lateral spreading of the cooling fluid.Copyright © 2008 by ASME

Large-Eddy Simulation of Film Cooling Flow Ejected in a Shallow Cavity

A verification and validation study was performed using the open source computational fluid dynamics software package OpenFOAM version 6-dev for conjugate heat transfer problems. The test cases had a growing complexity starting from a simple steady state problem over unsteady heat transfer to more realistic engineering applications. First, a fin effectiveness study was performed. Then, the external convection at pipes and internal pipe heat transfer were investigated. The validity of the techniques was shown for each test case by comparing the simulation results with experimental and analytic data available in the literature. Finally, a simplified shell-and-tube heat exchanger was simulated to demonstrate how these methods can be applied to plant scale engineering problems.

Peter Renze

Papers

Large-eddy simulation of film cooling flows at density gradients

Large-eddy Simulation of Film Cooling Flows with Variable Density Jets

Noise prediction for a turbulent jet using different hybrid methods

Large-Eddy Simulation of Film Cooling Flow Ejected in a Shallow Cavity

Simulation of Conjugate Heat Transfer in Thermal Processes with Open Source CFD