Heat transfer from turbulent separated flows

1967 ◽  
Vol 27 (1) ◽  
pp. 97-109 ◽  
Author(s):  
D. B. Spalding
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Separated Flow ◽  
Separated Flows ◽  
Two Dimensional ◽  
Hydrodynamic Properties ◽  
One Dimensional ◽  
Actual Mechanism ◽  
Turbulent Separated Flow

A power-law relation is derived between the Stanton number and the Reynolds number, expressing the law of heat transfer for a wall adjacent to a region of turbulent separated flow. The derivation is based on Prandtl's (1945) proposal for the laws of dissipation, diffusion and generation of turbulent kinetic energy. The constants appearing in these laws are determined by reference to experimental data for the hydrodynamic properties of the constant-stress and the linear-stress layers.The agreement between the resulting predictions and the experimental data of other workers is sufficiently good to suggest that the actual mechanism of heat transfer from separated flows has much in common with that which is postulated. Closer agreement can be expected only after the present one-dimensional analysis has been superseded by a two-dimensional one.

Base Heat Transfer in Two-Dimensional Subsonic Fully Separated Flows

1971 ◽  
Vol 93 (4) ◽  
pp. 342-348 ◽  
Author(s):  
John W. Mitchell
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Experimental Investigation ◽  
Vortex Shedding ◽  
Separated Flow ◽  
Flow Region ◽  
Separated Flows ◽  
Two Dimensional ◽  
Layer Behavior ◽  
Low Speed Wind Tunnel

An experimental investigation of the heat transfer from the base of a two-dimensional wedge-shaped body to the separated-flow region was conducted in a low-speed wind tunnel. The Stanton number has been determined as a function of Reynolds number for two geometries that are representative of heat-exchanger surfaces. The heat transfer is found to be comparable in magnitude to that for attached flows. An analysis based on the mechanisms of vortex shedding and boundary-layer behavior is developed. The analysis agrees fairly well with the data and indicates the parameters governing base heat transfer.

An OpenFOAM-Based Extension of Low-Re k–ε Model to the Partially Averaged Navier–Stokes Methodology for Simulating Separated Flows With Heat Transfer

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Krishnendu Chakraborty ◽  
Sagar Saroha ◽  
Sawan S. Sinha
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Computational Cost ◽  
Separated Flow ◽  
Classical Case ◽  
Separated Flows ◽  
Navier Stokes ◽  
Computational Time ◽  
Square Cylinder ◽  
Improved Performance

Abstract The partially averaged Navier–Stokes (PANS) methodology is known to give improved performance over the traditional Reynolds-averaged Navier–Stokes (RANS) formulation at an affordable computational cost. Over the years, PANS has gained popularity in both industry and academia. In this work, we strive to improve the performance of the k–ε-based PANS methodology by formulating a low-Reynolds-number (LRN) k–ε model-based PANS closure. We have compared the PANS closure based on Launder-Sharma k–ε model (LSKE) with PANS closure based on the conventional two-layer k–ε model (TLKE) in the classical case of separated flow past a heated square cylinder at Reynolds number (Re) of 21,400. The PANS methodologies are compared on the basis of flow hydrodynamics, heat transfer rate, and computational time. These methodologies are compared with the benchmark experimental and direct numerical simulation (DNS) results. The PANS + LSKE methodology clearly outperforms the conventional PANS + TLKE methodology in predicting the flow hydrodynamics and is computationally much faster as well. Moreover, the performance of the LSKE model in conjunction with the PANS methodology is found to be comparable to the more recent models like the shear stress transport (SST)–k–ω and the k–ε–ζ–f model. In heat transfer aspects, the performance of LSKE (with Yap correction)-based closure is the best on the stagnation surface, while the LSKE (without Yap correction)-based closure performs comparably better on the lateral and rear surfaces.

Predictions of a Turbulent Separated Flow Using Commercial CFD Codes

2001 ◽  
Vol 123 (4) ◽  
pp. 819-828 ◽  
Author(s):  
Gianluca Iaccarino
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Separation Bubble ◽  
Separated Flow ◽  
Adverse Pressure Gradient ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Flow Features ◽  
The Mean ◽  
Turbulent Separated Flow

Numerical simulations of the turbulent flow in an asymmetric two-dimensional diffuser are carried out using three commercial CFD codes: CFX, Fluent, and Star-CD. A low-Reynolds number k-ε model with damping functions and the four-equation v′2¯−f model are used; the first one is available as a standard feature in all the codes, the v′2¯−f model was implemented using the User Defined Routines. The flow features a large recirculating zone due to the adverse pressure gradient in the diffuser; the v′2¯−f predictions agree very well with the experiments both for the mean velocity and the turbulent kinetic energy. The length of the separation bubble is also computed within 6 percent of the measured value. The k-ε calculations do not show any recirculation and the agreement with the measurements is very poor. The three codes employed show very similar characteristics in terms of convergence and accuracy; in particular, the results obtained using the v′2¯−f are consistent in all the codes, while appreciable differences are obtained when the k-ε is employed.

scholarly journals Heat Transfer in Highly Turbulent Separated Flows: A Review

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1005
Author(s):  
Viktor I. Terekhov
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Separated Flow ◽  
Separated Flows ◽  
Turbulence Characteristic ◽  
Wall Jets ◽  
Average Heat ◽  
Free Stream Turbulence ◽  
External Turbulence ◽  
Near Wall

The study of flows with a high degree of turbulence in boundary layers, near-wall jets, gas curtains, separated flows behind various obstacles, as well as during combustion is of great importance for increasing energy efficiency of the flow around various elements in the ducts of gas-dynamic installations. This paper gives some general characteristics of experimental work on the study of friction and heat transfer on a smooth surface, in near-wall jets, and gas curtains under conditions of increased free-stream turbulence. Taking into account the significant effect of high external turbulence on dynamics and heat transfer of separated flows, a similar effect on the flow behind various obstacles is analyzed. First of all, the classical cases of flow separation behind a single backward-facing step and a rib are considered. Then, more complex cases of the flow around a rib oriented at different angles to the flow are analyzed, as well as a system of ribs and a transverse trench with straight and inclined walls in a turbulent flow around them. The features of separated flow in a turbulized stream around a cylinder, leading to an increase in the width of the vortex wake, frequency of vortex separation, and increase in the average heat transfer coefficient are analyzed. The experimental results of the author are compared with data of other researchers. The structure of separated flow at high turbulence—characteristic dimensions of the separation region, parameters of the mixing layer, and pressure distribution—are compared with the conditions of low-turbulent flow. Much attention is paid to thermal characteristics: temperature profiles across the shear layer, temperature distributions over the surface, and local and average heat transfer coefficients. It is shown that external turbulence has a much stronger effect on the separated flow than on the boundary layer on a flat surface. For separated flows, its intensifying effect on heat transfer is more pronounced behind a rib than behind a step. The factor of heat transfer intensification by external turbulence is most pronounced in the transverse cavity and in the system of ribs.

Effects of Heat Transfer During Peristaltic Transport in Nonuniform Channel With Permeable Walls

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Siddharth Shankar Bhatt ◽  
Amit Medhavi ◽  
R. S. Gupta ◽  
U. P. Singh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Incompressible Fluid ◽  
Friction Force ◽  
Viscous Incompressible Fluid ◽  
Peristaltic Transport ◽  
Two Dimensional ◽  
Peristaltic Motion ◽  
Long Wavelength ◽  
Permeable Walls

In the present investigation, problem of heat transfer has been studied during peristaltic motion of a viscous incompressible fluid for two-dimensional nonuniform channel with permeable walls under long wavelength and low Reynolds number approximation. Expressions for pressure, friction force, and temperature are obtained. The effects of different parameters on pressure, friction force, and temperature have been discussed through graphs.

A Viscous-Inviscid Interaction Procedure—Part 1: Method for Computing Two-Dimensional Incompressible Separated Channel Flows

1986 ◽  
Vol 108 (1) ◽  
pp. 64-70 ◽  
Author(s):  
O. K. Kwon ◽  
R. H. Pletcher
Keyword(s):  
Experimental Data ◽  
Finite Difference ◽  
Turbulent Flows ◽  
Inviscid Flow ◽  
Companion Paper ◽  
Separated Flows ◽  
Two Dimensional ◽  
Boundary Layer Equations ◽  
Interaction Scheme ◽  
Laminar And Turbulent Flows

A viscous-inviscid interaction scheme has been developed for computing steady incompressible laminar and turbulent flows in two-dimensional duct expansions. The viscous flow solutions are obtained by solving the boundary-layer equations inversely in a coupled manner by a finite-difference scheme; the inviscid flow is computed by numerically solving the Laplace equation for streamfunction using an ADI finite-difference procedure. The viscous and inviscid solutions are matched iteratively along displacement surfaces. Details of the procedure are presented in the present paper (Part 1), along with example applications to separated flows. The results compare favorably with experimental data. Applications to turbulent flows over a rearward-facing step are described in a companion paper (Part 2).

Numerical Study on Heat Transfer Characteristics From Parallel Plates With Cavities Swept by a Visco-Elastic Fluid

2010 ◽  
Author(s):  
Hiroshi Suzuki ◽  
Shinpei Maeda ◽  
Yoshiyuki Komoda
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Field ◽  
Numerical Study ◽  
Geometric Parameters ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Heat Transfer Characteristics ◽  
Elastic Fluid ◽  
Heat Transfer Augmentation

Two-dimensional numerical computations have been performed in order to investigate the development characteristics of flow and thermal field in a flow between parallel plates swept by a visco-elastic fluid. In the present study, the effect of the cavity number in the domain and of Reynolds number was focused on when the geometric parameters were set constant. From the results, it is found that the flow penetration into the cavities effectively causes the heat transfer augmentation in the cavities in any cavity region compared with that of water case. It is also found that the development of thermal field in cases of the present visco-elastic fluid is quicker compared with that of water cases. The present heat transfer augmentation technique using Barus effect of a visco-elastic fluid is effective in the range of low Reynolds number.

Jet-to-Plate Distance Effect on Heat Transfer From a Flat Plate to an Impinging Jet at Various Reynolds Numbers

2012 ◽  
Author(s):  
Patricia Streufert ◽  
Terry X. Yan ◽  
Mahdi G. Baygloo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Air Jet ◽  
Plate Distance

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.

Modeling of Mixed Convection Between Vertical Parallel Plates in Electric Equipment Immersed in High-Pr Liquids

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Thomas B. Gradinger ◽  
T. Laneryd
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Mixed Boundary ◽  
Mixed Boundary Conditions ◽  
Two Dimensional ◽  
Parallel Plates ◽  
One Dimensional ◽  
Electric Equipment

Natural-convection cooling with oil or other fluids of high Prandtl number plays an important role in many technical applications such as transformers or other electric equipment. For design and optimization, one-dimensional (1D) flow models are of great value. A standard configuration in such models is flow between vertical parallel plates. Accurate modeling of heat transfer, buoyancy, and pressure drop for this configuration is therefore of high importance but gets challenging as the influence of buoyancy rises. For increasing ratio of Grashof to Reynolds number, the accuracy of one-dimensional models based on the locally forced-flow assumption drops. In the present work, buoyancy corrections for use in one-dimensional models are developed and verified. Based on two-dimensional (2D) simulations of buoyant flow using finite-element solver COMSOL Multiphysics, corrections are derived for the local Nusselt number, the local friction coefficient, and a parameter relating velocity-weighted and volumetric mean temperature. The corrections are expressed in terms of the ratio of local Grashof to Reynolds number and a normalized distance from the channel inlet, both readily available in a one-dimensional model. The corrections universally apply to constant wall temperature, constant wall heat flux, and mixed boundary conditions. The developed correlations are tested against two-dimensional simulations for a case of mixed boundary conditions and are found to yield high accuracy in temperature, wall heat flux, and wall shear stress. An application example of a natural-convection loop with two finned heat exchangers shows the influence on mass-flow rate and top-to-bottom temperature difference.

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