Predicting Skin Friction and Heat Transfer for Turbulent Flow Over Real Gas-Turbine Surface Roughness Using the Discrete-Element Method

Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons

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 through the fluid on the flat part of the surface and the convection from each of the roughness elements. The discrete-element method has been widely used and validated for predicting heat transfer and skin friction for rough surfaces composed of sparse, ordered, and deterministic elements. Real gas-turbine surface roughness is different from surfaces with sparse, ordered, and deterministic roughness elements. Modifications made to the discrete-element roughness method to extend the validation to real gas-turbine surface roughness are detailed. Two rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. Two rough surfaces and two elliptical-analog surfaces were generated for wind-tunnel testing using a three-dimensional printer. The printed surfaces were scaled to maintain similar boundary-layer thickness to roughness height ratio in the wind tunnel as found in gas-turbine operation. The results of the wind tunnel skin friction and Stanton number measurements and the discrete-element method predictions for each of the four surfaces are presented and discussed. The discrete-element predictions made considering the gas-turbine roughness modifications are within 7% of the experimentally-measured skin friction coefficients and are within 16% of the experimentally-measured Stanton numbers.

2004 ◽  
Vol 126 (2) ◽  
pp. 259-267 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons

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 through the fluid on the flat part of the surface and the convection from each of the roughness elements. The discrete element method has been widely used and validated for predicting heat transfer and skin friction for rough surfaces composed of sparse, ordered, and deterministic elements. Real gas turbine surface roughness is different from surfaces with sparse, ordered, and deterministic roughness elements. Modifications made to the discrete element roughness method to extend the validation to real gas turbine surface roughness are detailed. Two rough surfaces found on high-hour gas turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. Two rough surfaces and two elliptical-analog surfaces were generated for wind tunnel testing using a three-dimensional printer. The printed surfaces were scaled to maintain similar boundary layer thickness to roughness height ratio in the wind tunnel as found in gas turbine operation. The results of the wind tunnel skin friction and Stanton number measurements and the discrete element method predictions for each of the four surfaces are presented and discussed. The discrete element predictions made considering the gas turbine roughness modifications are within 7% of the experimentally measured skin friction coefficients and are within 16% of the experimentally measured Stanton numbers.


Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons

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.


Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons

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.


Clean Energy ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 141-166
Author(s):  
Bing Liu

Abstract An algorithm using the discrete element method (DEM) for simulating the particulate behaviour of flow and heat transfer is developed and described, the reasonable hypothesis and the ingenious design of which have been presented in detail. The organizational structure of the developed algorithm contains an efficient method for determining particle collisions, the status analysis for each particle and the particulate-kinematics analysis during the time step. The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments: the discharge process of glass beads from a silo; and heating of metal alloy particles in a calciner. Afterwards, a group of validated mechanics parameter values for coal and sand have been tested and verified in the article, preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.


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