Heat Transfer Measurements and Calculations in Transitionally Rough Flow

1991 ◽  
Vol 113 (3) ◽  
pp. 404-411 ◽  
Author(s):  
M. H. Hosni ◽  
H. W. Coleman ◽  
R. P. Taylor
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Rough Surface ◽  
Element Model ◽  
Discrete Element ◽  
Skin Friction Coefficient ◽  
Stanton Number ◽  
Transfer Model ◽  
Layer Flow ◽  
Prediction Approach

Experimental data on a rough surface for both transitionally rough and fully rough turbulent flow regimes are presented for Stanton number distribution, skin friction coefficient distribution, and turbulence intensity profiles. The rough surface is composed of 1.27-mm-dia hemispheres spaced in a staggered array four base diameters apart on an otherwise smooth wall. Special emphasis is placed on the characteristics of heat transfer in the transitionally rough flows. Stanton number data are reported for zero pressure gradient incompressible turbulent boundary layer air flow for nominal free-stream velocities of 6, 12, 28, 43, 58, and 67 m/s, which give x-Reynolds numbers up to 10,000,000. These data are compared with previously published rough surface data, and the classification of a boundary layer flow into transitionally rough and fully rough regimes is explored. Moreover, a new heat transfer model for use in the previously published discrete element prediction approach is presented. Computations using the discrete element model are presented and compared with data obtained from two different rough surfaces. The discrete element predictions for both surfaces are found to be in substantial agreement with the data.

Heat Transfer Measurements and Calculations in Transitionally Rough Flow

1990 ◽  
Author(s):  
M. H. Hosni ◽  
Hugh W. Coleman ◽  
Robert P. Taylor
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Rough Surface ◽  
Element Model ◽  
Discrete Element ◽  
Skin Friction Coefficient ◽  
Stanton Number ◽  
Transfer Model ◽  
Layer Flow ◽  
Prediction Approach

Experimental data on a rough surface for both transitionally rough and fully rough turbulent flow regimes are presented for Stanton number distribution, skin friction coefficient distribution and turbulence intensity profiles. The rough surface is composed of 1.27 mm diameter hemispheres spaced in a staggered array four base diameters apart on an otherwise smooth wall. Special emphasis is placed on the characteristics of heat transfer in the transitionally rough flows. Stanton number data are reported for zero pressure gradient incompressible turbulent boundary layer air flow for nominal freestream velocities of 6, 12, 28, 43, 58 and 67 m/s, which give x-Reynolds numbers up to 10,000,000. These data are compared with previously published rough surface data, and the classification of a boundary layer flow into transitionally rough and fully rough regimes is explored. Moreover, a new heat transfer model for use in the previously published discrete element prediction approach is presented. Computations using the discrete element model are presented and compared with data obtained from two different rough surfaces. The discrete element predictions for both surfaces are found to be in substantial agreement with the data.

A Comparison of Approximate Versus Exact Geometrical Representations of Roughness for CFD Calculations of cf and St

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
J. P. Bons ◽  
S. T. McClain ◽  
Z. J. Wang ◽  
X. Chi ◽  
T. I. Shih
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Rough Surface ◽  
Turbulence Model ◽  
Rough Surfaces ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Flat Part ◽  
Roughness Elements

Skin friction (cf) and heat transfer (St) predictions were made for a turbulent boundary layer over randomly rough surfaces at Reynolds number of 1×106. The rough surfaces are scaled models of actual gas turbine blade surfaces that have experienced degradation after service. Two different approximations are used to characterize the roughness in the computational model: the discrete element model and full 3D discretization of the surface. The discrete element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection on the flat part of the surface and the convection from each of the roughness elements. Correlations are used to model the roughness element drag and heat transfer, thus avoiding the complexity of gridding the irregular rough surface. The discrete element roughness representation was incorporated into a two-dimensional, finite difference boundary layer code with a mixing length turbulence model. The second prediction method employs a viscous adaptive Cartesian grid approach to fully resolve the three-dimensional roughness geometry. This significantly reduces the grid requirement compared to a structured grid. The flow prediction is made using a finite-volume Navier-Stokes solver capable of handling arbitrary grids with the Spalart-Allmaras (S‐A) turbulence model. Comparisons are made to experimentally measured values of cf and St for two unique roughness characterizations. The two methods predict cf to within ±8% and St within ±17%, the RANS code yielding slightly better agreement. In both cases, agreement with the experimental data is less favorable for the surface with larger roughness features. The RANS simulation requires a two to three order of magnitude increase in computational time compared to the DEM method and is not as readily adapted to a wide variety of roughness characterizations. The RANS simulation is capable of analyzing surfaces composed primarily of roughness valleys (rather than peaks), a feature that DEM does not have in its present formulation. Several basic assumptions employed by the discrete element model are evaluated using the 3D RANS flow predictions, namely: establishment of the midheight for application of the smooth wall boundary condition; cD and Nu relations employed for roughness elements; and flow three dimensionality over and around roughness elements.

A Comparison of Approximate vs. Exact Geometrical Representations of Roughness for CFD Calculations of CF and ST

2005 ◽  
Author(s):  
J. P. Bons ◽  
S. T. McClain ◽  
Z. J. Wang ◽  
X. Chi ◽  
T. I. Shih
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Rough Surface ◽  
Turbulence Model ◽  
Rough Surfaces ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Flat Part ◽  
Roughness Elements

Skin friction (cf) and heat transfer (St) predictions were made for a turbulent boundary layer over randomly rough surfaces at Reynolds number of 1 × 106. The rough surfaces are scaled models of actual gas turbine blade surfaces that have experienced degradation after service. Two different approximations are used to characterize the roughness in the computational model: the discrete element model and full 3-D discretization of the surface. The discrete element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection on the flat part of the surface and the convection from each of the roughness elements. Correlations are used to model the roughness element drag and heat transfer thus avoiding the complexity of gridding the irregular rough surface. The discrete element roughness representation was incorporated into a two-dimensional, finite difference boundary layer code with a mixing length turbulence model. The second prediction method employs a viscous adaptive Cartesian grid approach to fully resolve the three-dimensional roughness geometry. This significantly reduces the grid requirement compared to a structured grid. The flow prediction is made using a finite-volume Navier-Stokes solver capable of handling arbitrary grids with the Spalart-Allmaras (S-A) turbulence model. Comparisons are made to experimentally measured values of cf and St for two unique roughness characterizations. The two methods predict cf to within ±8% and St within ±17%, the RANS code yielding slightly better agreement. In both cases, agreement with the experimental data is less favorable for the surface with larger roughness features. The RANS simulation requires a two to three order of magnitude increase in computational time compared to the DEM method and is not as readily adapted to a wide variety of roughness characterizations. The RANS simulation is capable of analyzing surfaces composed primarily of roughness valleys (rather than peaks), a feature that DEM does not have in its present formulation. Several basic assumptions employed by the discrete element model are evaluated using the 3D RANS flow predictions, namely: establishment of the mid-height for application of the smooth wall boundary condition, cD and Nu relations employed for roughness elements, and flow three-dimensionality over and around roughness elements.

Reduced Rough-Surface Parametrization for Use With the Discrete-Element Model

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Stephen T. McClain ◽  
Jason M. Brown
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Diameter Distribution ◽  
Discrete Element Model

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly rough surface. The requirement for a roughness-element diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.

Reduced Rough-Surface Parameterization for Use With the Discrete-Element Model

2007 ◽  
Author(s):  
Stephen T. McClain ◽  
Jason M. Brown
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Three Dimensional ◽  
Element Model ◽  
Discrete Element ◽  
Diameter Distribution ◽  
Discrete Element Model

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly-rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly-rough surface. The requirement for a roughness element-diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly-rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly-rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.

Boundary layer flow near stagnation-points on a vertical surface with slip in the presence of transverse magnetic field

2014 ◽  
Vol 24 (3) ◽  
pp. 643-653 ◽  
Author(s):  
Ibrahim Yakubu Seini ◽  
Daniel Oluwole Makinde
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Boundary Layer ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Stagnation Point ◽  
Vertical Surface ◽  
Skin Friction Coefficient ◽  
Content Type ◽  
Layer Flow

Purpose – The purpose of this paper is to investigate the MHD boundary layer flow of viscous, incompressible and electrically conducting fluid near a stagnation-point on a vertical surface with slip. Design/methodology/approach – In the study, the temperature of the surface and the velocity of the external flow are assumed to vary linearly with the distance from the stagnation-point. The governing differential equations are transformed into systems of ordinary differential equations and solved numerically by a shooting method. Findings – The effects of various parameters on the heat transfer characteristics are discussed. Graphical results are presented for the velocity and temperature profiles whilst the skin-friction coefficient and the rate of heat transfers near the surface are presented. It is observed that the presence of the magnetic field increases the skin-friction coefficient and the rate of heat transfer near the surface towards the stagnation-point. Originality/value – The presence of magnetic field increases the skin-friction coefficient and the rate of heat transfer near the surface towards the stagnation-point.

scholarly journals Hydromagnetic boundary layer micropolar fluid flow over a stretching surface embedded in a non-darcian porous medium with radiation

2006 ◽  
Vol 2006 ◽  
pp. 1-10 ◽  
Author(s):  
Mostafa A. A. Mahmoud ◽  
Mahmoud Abd-elaty Mahmoud ◽  
Shimaa E. Waheed
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Porous Medium ◽  
Micropolar Fluid ◽  
Skin Friction Coefficient ◽  
Stretching Surface ◽  
Electrically Conducting ◽  
Micropolar Fluid Flow ◽  
Layer Flow ◽  
Effects Of Radiation

We have studied the effects of radiation on the boundary layer flow and heat transfer of an electrically conducting micropolar fluid over a continuously moving stretching surface embedded in a non-Darcian porous medium with a uniform magnetic field. The transformed coupled nonlinear ordinary differential equations are solved numerically. The velocity, the angular velocity, and the temperature are shown graphically. The numerical values of the skin friction coefficient, the wall couple stress, and the wall heat transfer rate are computed and discussed for various values of parameters.

Mixed Convection in Viscoelastic Boundary Layer Flow and Heat Transfer Over a Stretching Sheet

2014 ◽  
Vol 6 (3) ◽  
pp. 359-375 ◽  
Author(s):  
Antonio Mastroberardino
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Skin Friction Coefficient ◽  
Convection Boundary Layer ◽  
Electrically Conducting ◽  
Homotopy Analysis ◽  
Layer Flow

AbstractAn investigation is carried out on mixed convection boundary layer flow of an incompressible and electrically conducting viscoelastic fluid over a linearly stretching surface in which the heat transfer includes the effects of viscous dissipation, elastic deformation, thermal radiation, and non-uniform heat source/sink for two general types of non-isothermal boundary conditions. The governing partial differential equations for the fluid flow and temperature are reduced to a nonlinear system of ordinary differential equations which are solved analytically using the homotopy analysis method (HAM). Graphical and numerical demonstrations of the convergence of the HAM solutions are provided, and the effects of various parameters on the skin friction coefficient and wall heat transfer are tabulated. In addition it is demonstrated that previously reported solutions of the thermal energy equation given in [1] do not converge at the boundary, and therefore, the boundary derivatives reported are not correct.

scholarly journals Melting Heat Transfer and MHD Boundary Layer Flow of Eyring-Powell Nanofluid Over a Nonlinear Stretching Sheet with Slip

2019 ◽  
Vol 24 (1) ◽  
pp. 161-178 ◽  
Author(s):  
N. Vijaya Bhaskar Reddy ◽  
N. Kishan ◽  
C. Srinivas Reddy
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Volume Fraction ◽  
Skin Friction Coefficient ◽  
Physical Parameters ◽  
Local Skin ◽  
Layer Flow ◽  
Nonlinear Stretching ◽  
The Impact

Abstract The steady laminar incompressible viscous magneto hydrodynamic boundary layer flow of an Eyring- Powell fluid over a nonlinear stretching flat surface in a nanofluid with slip condition and heat transfer through melting effect has been investigated numerically. The resulting nonlinear governing partial differential equations with associated boundary conditions of the problem have been formulated and transformed into a non-similar form. The resultant equations are then solved numerically using the Runge-Kutta fourth order method along with the shooting technique. The physical significance of different parameters on the velocity, temperature and nanoparticle volume fraction profiles is discussed through graphical illustrations. The impact of physical parameters on the local skin friction coefficient and rate of heat transfer is shown in tabulated form.

scholarly journals Boundary Layer Flow and Heat Transfer of Al2O3-TiO2/Water Hybrid Nanofluid over a Permeable Moving Plate

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1064
Author(s):  
Nur Adilah Liyana Aladdin ◽  
Norfifah Bachok
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Opposite Direction ◽  
Free Stream ◽  
Nonlinear Partial Differential Equation ◽  
Skin Friction Coefficient ◽  
Hybrid Nanofluid ◽  
Moving Plate ◽  
Heat Transfer Efficiency ◽  
Layer Flow

Hybrid nanofluid is considered a new type of nanofluid and is further used to increase the heat transfer efficiency. This paper explores the two-dimensional steady axisymmetric boundary layer which contains water (base fluid) and two different nanoparticles to form a hybrid nanofluid over a permeable moving plate. The plate is suspected to move to the free stream in the similar or opposite direction. Similarity transformation is introduced in order to convert the nonlinear partial differential equation of the governing equation into a system of ordinary differential equations (ODEs). Then, the ODEs are solved using bvp4c in MATLAB 2019a software. The mathematical hybrid nanofluid and boundary conditions under the effect of suction, S, and the concentration of nanoparticles, ϕ 1 (Al2O3) and ϕ 2 (TiO2) are taken into account. Numerical results are graphically described for the skin friction coefficient, C f , and local Nusselt number, N u x , as well as velocity and temperature profiles. The results showed that duality occurs when the plate and the free stream travel in the opposite direction. The range of dual solutions expand widely for S and closely reduce for ϕ . Thus, a stability analysis is performed. The first solution is stable and realizable compared to the second solution. The C f and N u x increase with the increment of S. It is also noted that the increase of ϕ 2 leads to an increase in C f and decrease in N u x .

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