Effects of Free-Stream Turbulence and Reynolds Number on the Aerodynamic Characteristics of a Semicylindrical Roof

摘要

The influences of free-stream turbulence and Reynolds number on the aerodynamic characteristics of a semicylindrical roof have been investigated experimentally under uniform flow conditions. Grids were used to generate homogeneous turbulent flows with turbulence intensities varying from 5.7 to 12.2%. The diameters, D, of the semicylindrical roof models were 0.2 and 0.6 m. The Reynolds numbers based on D ranged from 6.90 x 10(4) to 8.28 x 10(5) in smooth flow and from approximately 6.06 x 10(4) to 4.79 x 10(5) in grid-generated turbulent flow. Measurements of the surface pressure indicated that, in smooth flow, the mean and RMS pressure distributions became Reynolds number independent when R > 4.14 x 10(5). The introduction of turbulence has caused a premature transition of the separated shear layer from laminar to turbulent. Increasing free-stream turbulence helps to remarkably reduce the mean and fluctuating drag force at lower Reynolds number, R < 1.46 x 10(5). There is also a relatively significant reduction in the mean lift force as the turbulence intensity increases when R > 1.46 x 10(5). The data also suggested that the effects of turbulence essentially depend on the turbulence intensity and the ratio of turbulence length scale to cylinder diameter. The small-scale turbulence was better able to interact with the surface boundary layer before and after separation and thus dramatically increased the pressure fluctuations in both the top and wake regions. (C) 2014 American Society of Civil Engineers.