Measurements of the Influence of Integral Length Scale on Stagnation Region Heat Transfer

[摘要] The purpose of the present work was twofold: first, to determine if a length scale existed thatwould cause the greatest augmentation in stagnation region heat transfer for a given turbulenceintensity and second, to develop a prediction tool for stagnation heat transfer in thepresence of free stream turbulence. Toward this end, a model with a circular leading edgewas fabricated with heat transfer gages in the stagnation region. The model was qualified ina low turbulence wind tunnel by comparing measurements with Frossling's solution forstagnation region heat transfer in a laminar free stream. Five turbulence generating gridswere fabricated; four were square mesh, biplane grids made from square bars. Each hadidentical mesh to bar width ratio but different bar widths. The fifth grid was an array of fineparallel wires that were perpendicular to the axis of the cylindrical leading edge. Turbulenceintensity and integral length scale were measured as a function of distance from the grids.Stagnation region heat transfer was measured at various distances downstream of each grid.Data were taken at cylinder Reynolds numbers ranging from 42,000 to 193,000. Turbulenceintensities were in the range 1.1 to 15.9 percent while the ratio of integral length scale tocylinder diameter ranged from 0.05 to 0.30. Stagnation region heat transfer augmentationincreased with decreasing length scale. An optimum scale was not found. A correlation wasdeveloped that fit heat transfer data for the square bar grids to within ±4%. The data fromthe array of wires were not predicted by the correlation; augmentation was higher for thiscase indicating that the degree of isotropy in the turbulent flow field has a large effect onstagnation heat transfer. The data of other researchers are also compared with the correlation.

[学科分类] 力学，机械学