Multifidelity Analysis of Acoustic Streaming in Forced Convection Heat Transfer

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Tapish Agarwal ◽  
Iman Rahbari ◽  
Jorge Saavedra ◽  
Guillermo Paniagua ◽  
Beni Cukurel
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Parameter Space ◽  
Research Effort ◽  
Spatial Scales ◽  
Acoustic Streaming ◽  
Laminar Flows ◽  
Secondary Flows ◽  
Reynolds Analogy ◽  
Laminar Model

Abstract This research effort is related to the detailed analysis of the temporal evolution of thermal boundary layer(s) under periodic excitations. In the presence of oscillations, the nonlinear interaction leads to the formation of secondary flows, commonly known as acoustic streaming. However, the small spatial scales and the inherent unsteady nature of streaming have presented challenges for prior numerical investigations. In order to address this void in numerical framework, the development of a three-tier numerical approach is presented. As a first layer of fidelity, a laminar model is developed for fluctuations and streaming flow calculations in laminar flows subjected to traveling wave disturbances. At the next level of fidelity, two-dimensional (2D) U-RANS simulations are conducted across both laminar and turbulent flow regimes. This is geared toward extending the parameter space obtained from laminar model to turbulent flow conditions. As the third level of fidelity, temporally and spatially resolved direct numerical simulation (DNS) simulations are conducted to simulate the application relevant compressible flow environment. The exemplary findings indicate that in certain parameter space, both enhancement and reduction in heat transfer can be obtained through acoustic streaming. Moreover, the extent of heat transfer modulations is greater than alterations in wall shear, thereby surpassing Reynolds analogy.

Multi-Fidelity Analysis of Acoustic Streaming in Forced Convection Heat Transfer

2019 ◽  
Author(s):  
Tapish Agarwal ◽  
Iman Rahbari ◽  
Jorge Saavedra ◽  
Guillermo Paniagua ◽  
Beni Cukurel
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Forced Convection ◽  
Parameter Space ◽  
Thermal Boundary Layer ◽  
Acoustic Streaming ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Wave Disturbances

Abstract The behavioral characteristics of thermal boundary layer dictate the relative efficiency of forced convection heat transfer. This research effort is related to the detailed analysis of the temporal evolution of thermal boundary layer under periodic excitations. In presence of oscillations, a distinct thin Stokes layer is formed inside the attached boundary layer, which interacts nonlinearly with the mean flow in the near wall region. This interaction leads to modification of temporally averaged flow fields, commonly known as acoustic streaming. As a result, the aero-thermal wall gradients are modified leading to significant changes in wall shear stress and heat flux. However, the small spatial scales and the inherent unsteady nature of streaming has presented challenges for prior numerical investigations, preventing the identification of optimal parameters. In order to address this void in numerical framework, the development of a three-tier numerical approach is presented. As a first layer of fidelity, a laminar model is developed for fluctuations and streaming flow calculations in laminar flows subjected to travelling wave disturbances. This technique is an extension of the Lin’s method to traveling wave disturbances of various speeds (absent of previously employed assumptions), along with inclusion of energy equation. With low computational cost, this level of abstraction is intended to identify the broad parameter space that yield desirable heat transfer alterations. At the next level of fidelity, 2D U-RANS simulations are conducted across both laminar and turbulent flow regimes. This is geared towards extending the parameter space obtained from laminar model to turbulent flow conditions. As the third level of fidelity, temporally and spatially resolved DNS simulations are conducted to simulate the application relevant compressible flow environment. The exemplary findings indicate that in certain parameter space, both enhancement and reduction in heat transfer can be obtained through acoustic streaming. Moreover, the extent of heat transfer modulations is greater than alterations in wall shear, thereby surpassing Reynolds analogy.

Heat Transfer and Surface Friction Downstream of a Dual Array of Dimples of a Different Shape

2008 ◽  
Author(s):  
Artem Khalatov ◽  
Vitaliy Onishchenko
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Test Section ◽  
Low Reynolds Number ◽  
Surface Friction ◽  
Experimental Program ◽  
Reynolds Analogy ◽  
Low Reynolds

The wide experimental program was carried out in the Institute for Engineering Thermophysics (Kiev, Ukraine) to study heat transfer and surface friction downstream of the dual array of dimples. The test section is the rectangular channel 34 mm height, 290 mm wide and 125 mm long. The unheated dual array of dimples was placed on the channel floor (bottom) wall upstream of the electrically heated test section. Inserts with dimples of spherical, cylindrical and square shape were tested at their relative depth h/D of 0.20 and 0.30. Projected (surface) diameter of dimples is 25.0 mm; the second row was placed in the staggered fashion with the downstream pitch Sx/D of 0.64. The span-wise spacing Sz/D is of 2.0 providing the second row exactly fills in the open span-wise gap between dimples in the first row. The inlet air speed was from 4.1 to 16.6 m/c, Reynolds number Re2H, based on the equivalent (hydraulic) channel diameter varied from 17,400 to 71,800, the inlet boundary layer thickness did not exceed 1.0 mm. According to shape factor measurements the turbulent flow existed in front of dimples for all flow conditions tested. Heat transfer measurements were performed over the center line downstream of the representative dimple placed in the first or second row. The Reynolds number Rex based on the downstream distance was ranged from 3,000 to 105,000. Based on measurements, the conclusion was made that immediately after dimple array (at Rex>3,000) heat transfer corresponds to the turbulent flow data for a smooth flat plate extended into the low Reynolds number area. The downstream heat transfer ratio Nux/Nu0 weakly depends on the dimple shape and depth. The downstream surface friction τw was measured over the central line beyond the dimple placed in the first or second row. The tube-in-flow technique was employed in these measurements. At low probe distances (x/D = 1.2–2.4) the surface friction coefficients locate between classic correlations for the laminar and turbulent flow (extended into the low Reynolds number area) for a smooth flat plate. At high probe distances (x/D > 4.16) the surface friction data agrees well with the classic turbulent flow correlation for the smooth flat plate. Close to the dimple downstream edge (x/D < 2.4) the Reynolds analogy factor is over the unity for all dimple depths and geometries, thus confirming the greater heat transfer increases compared with pressure drop growth. At higher distances, the Reynolds analogy factor is above or below the Reynolds analogy line (RAF = 1.0) depending on the dimple shape and depth. Comparisons on the Reynolds analogy factor magnitude were made in terms of the downstream distances from the dimple back edge.

Analogy between turbulent flows in curved pipes and orthogonally rotating pipes

1996 ◽  
Vol 307 ◽  
pp. 1-10 ◽  
Author(s):  
Hiroshi Ishigaki
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Laminar Flows ◽  
Computational Results ◽  
Transfer Rates ◽  
Fundamental Parameters ◽  
Curved Pipes ◽  
Friction Factors

A quantitative analogy between fully developed turbulent flows in curved pipes and orthogonally rotating pipes will be described through similarity arguments, the use of experimental data and computational results. A pair of similarity parameters will be derived for each turbulent flow, so that they have the same dynamical meaning as those of laminar flows. When the second parameter for each flow is large enough, it will be shown that friction factors, as well as heat transfer rates, of the two flows coincide for equal values of the fundamental parameters. Computed contours of velocity and temperature will also reveal strong similarities between the two flows.

An appraisal of ‘flat plate’ closure for the approximate solution of boundary layer problems

1987 ◽  
Vol 91 (908) ◽  
pp. 373-389
Author(s):  
D. I. A. Poll ◽  
C. M. Hellon
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mach Number ◽  
Flat Plate ◽  
High Speed ◽  
Compressible Flows ◽  
Incompressible Flows ◽  
Similarity Solutions ◽  
Laminar Flows ◽  
Reynolds Analogy

SummaryThe usefulness of zero pressure gradient, flat plate closure relations in providing approximate solutions for the boundary layer momentum and energy integral equations is examined. Expressions are obtained for skin friction, surface heat transfer rate and local Reynolds analogy factor under general compressible flow conditions. For laminar flows the predictions are compared with well known similarity solutions, with some exact solutions for non-similar flows and with experimental heat transfer data for high speed flow over a blunt cone. Consideration is also given to situations in which the surface temperature is a function of position. For turbulent flow situations comparisons are made with experimental data obtained from two-dimensional and axi-symmetric tests. Conditions vary from low Mach number incompressible flows through to high Mach number compressible flows with highly cooled walls. Some comparisons are also made with other prediction techniques.

Numerical Prediction of Turbulent Flow and Heat Transfer Within Ducts of Cross-Shaped Cross Section

1986 ◽  
Vol 108 (4) ◽  
pp. 841-847 ◽  
Author(s):  
A. Nakayama ◽  
H. Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Secondary Flows ◽  
Turbulent Heat Transfer ◽  
Parallel Plates ◽  
Reynolds Analogy ◽  
The Heat Transfer Coefficient ◽  
Shaped Cross Section

Calculations were carried out for fully developed turbulent flows within ducts of cross-shaped cross section using the numerical method based on the pressure correction method developed by Patankar and Spalding. The Reynolds stress driven secondary flows were simulated successfully by Launder and Ying’s algebraic stress model coupled to the k–ε turbulence model. A parametric study was made on the friction and heat transfer characteristics in terms of the parameter α associated with the decrease in the cross-sectional area, namely, α = 0 for a square duct, and α → 1 for infinite parallel plates. Through performance evaluations, it has been found that both the Reynolds analogy factor and the heat transfer coefficient under equal pumping power decrease slightly, while the heat transfer coefficient obtained with equal mass flow rate increases appreciably with α, suggesting effective turbulent heat transfer within ducts of cross-shaped cross section.

Large-Eddy Simulations of Low Pressure Turbine Endwall Flow and Heat Transfer

2018 ◽  
Author(s):  
Stephen Lynch
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Secondary Flow ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Secondary Flows ◽  
Reynolds Analogy ◽  
Low Pressure Turbine ◽  
Large Eddy

Turbine airfoils are subject to strong secondary flows that produce total pressure loss and high surface heat transfer in the airfoil passage. The secondary flows arise from the high overall flow turning acting on the incoming boundary layer, as well as the generation of a horseshoe vortex at the leading edge of the airfoil. Prediction of the effects of secondary flows on endwall heat transfer using steady Reynolds-averaged Navier-Stokes (RANS) approaches has so far been somewhat unsatisfactory, but it is unclear whether this is due to unsteadiness of the secondary flow, modeling assumptions (such as the Boussinesq approximation and Reynolds analogy), strongly non-equilibrium boundary layer behavior in the highly skewed endwall flow, or some combination of all. To address some of these questions, and to determine the efficacy of higher-fidelity computational approaches to predict endwall heat transfer, a low pressure turbine cascade was modeled using a wall-modeled Large Eddy Simulation (LES) approach. The result was compared to a steady Reynolds-stress modeling (RSM) approach, and to experimental data. Results indicate that the effect of the unsteadiness of the pressure side leg of the horseshoe vortex results in a broad distribution of heat transfer in the front of the passage, and high heat transfer on the aft suction side corner, which is not predicted by steady RANS. However, the time-mean heat transfer is still not well predicted due to slight differences in the secondary flow pattern. Turbulence quantities in the blade passage agree fairly well to prior measurements and highlight the effect of the strong passage curvature on the endwall boundary layer, but the LES approach here overpredicts turbulence in the secondary flow at the cascade outlet due to a thick airfoil suction side boundary layer. Overall, more work remains to identify the specific model deficiencies in RSM or wall-modeled LES approaches.

VISUALIZATION OF HEAT TRANSFER IN UNSTEADY LAMINAR FLOWS

2011 ◽  
Vol 3 (1) ◽  
pp. 31-47 ◽  
Author(s):  
Michel F. M. Speetjens ◽  
Anton A. van Steenhoven
Keyword(s):  
Heat Transfer ◽  
Laminar Flows
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