Predicting Skin Friction for Turbulent Flow Over Randomly-Rough Surfaces Using the Discrete-Element Method: Part I — Surface Characterization

2003 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Discrete Element Method ◽  
Turbulent Flow ◽  
Skin Friction ◽  
Rough Surface ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Discrete Element ◽  
Randomly Rough Surfaces ◽  
Randomly Rough Surface ◽  
Element Method

The discrete-element method for predicting skin friction for turbulent flow over rough surfaces considers the drag on the surface to result from the combination of the skin friction on the flat part of the surface and the drag on the individual roughness elements that protrude into the boundary layer. To adequately analyze flow over a randomly-rough surface using the discrete-element method, the blockage fraction and the roughness element cross-section area distributions as a function of height must be measured. Taylor, in 1983, proposed a method for evaluating the blockage fraction and cross-sectional areas distributions, assuming circular cross sections, using two-dimensional profilometer traces. With the advent of three-dimensional profilometery, the geometry of a randomly-rough surface can be completely characterized. Two randomly-rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. A method for using the three-dimensional profilometer output to determine the geometry input required in the discrete-element method for randomly-rough surfaces is presented in this paper, Part 1. Part 2 extends the validation of the discrete-element roughness method to closely-packed, randomly-rough surfaces. The procedure for handling randomly-rough surfaces is described, and the characterizations for the surfaces used to validate the discrete element model in Part 2 are presented.

Predicting Skin Friction for Turbulent Flow Over Randomly-Rough Surfaces Using the Discrete-Element Method: Part II — Skin Friction Validation

2003 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Surface Roughness ◽  
Wind Tunnel ◽  
Discrete Element Method ◽  
Turbulent Flow ◽  
Skin Friction ◽  
Rough Surfaces ◽  
Roughness Element ◽  
Discrete Element ◽  
Randomly Rough Surface ◽  
Element Method

The discrete-element method for predicting skin friction for turbulent flow over rough surfaces considers the drag on the surface to be the sum of the skin friction on the flat part of the surface and the drag on the individual roughness elements that protrude into the boundary layer. The discrete-element method has been widely used and validated for roughness composed of sparse, ordered, and deterministic elements. This paper extends the validation of the discrete-element to include real (random and closely packed) surface roughness. To analyze flow over a randomly-rough surface using the discrete-element method, the roughness element blockage fraction and the roughness element cross-section area distributions as a function of height must be determined from surface profilometer measurements. The technique developed for determining these distributions was described in Part 1. This paper, Part 2, describes the modifications that were made to the discrete-element roughness method to extend the validation to real surface roughness. These modifications include accounting for the deviation of the roughness element cross sections from circular configurations and the determination of the location of the computational “surface,” that differs from the physical surface. Two randomly-rough surfaces, two analog surfaces were generated using a three-dimensional printer for wind-tunnel testing. The analog surfaces were created by replacing each random roughness element from the original randomly-rough surface with an elliptical roughness element with the equivalent plan area and eccentricity. The results of the wind tunnel skin friction measurements and the discrete-element method predictions for each of the six surfaces are presented and discussed. For each randomly-rough and analog surface studied, the discrete-element method predictions are within 7% of the experimentally measured skin friction coefficients.

A generalized three-dimensional discrete element method with electrostatic induced cohesion

2020 ◽  
Vol 22 (4) ◽  
Author(s):  
Daniel Bustamante ◽  
Alex X. Jerves ◽  
Sebastián A. Pazmiño
Keyword(s):  
Discrete Element Method ◽  
Three Dimensional ◽  
Discrete Element ◽  
Element Method

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.

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