Abstract
An experimental study was done to quantify the effects of a variety of background particulates on the delayed laminar-turbulent transition of a thermally stabilized boundary layer in water. A Laser-Doppler Velocimeter system was used to measure the location of boundary layer transition on a 50 mm diameter, 9:1 fineness ratio ellipsoid. The ellipsoid had a 0.15 μm RMS surface finish. Boundary layer transition locations were determined for length Reynolds numbers ranging from 3.0 × 106 to 7.5 × 106. The ellipsoid was tested in three different heating conditions in water seeded with particles of four distinct size ranges. For each level of boundary layer heating, measurements of transition were made for “clean” water and subsequently, water seeded with 12.5 μm, 38.9 μm, 85.5 μm and 123.2 μm particles, alternately. The three surface heating conditions tested were no heating, ΔT = 10°C and ΔT = 15°C where ΔT is the difference between the inlet model heating water temperature, T i, and free stream water temperature, T ∞. The effects of particle concentration were studied for 85.5 μm and 123.2 μm particulates.
The results of the study can be summarized as follows. The 12.5 μm and 38.9 μm particles has no measurable effect on transition for any of the test conditions. However, transition was significantly affected by the 85.5 μm and 123.2 μm particles. Above a length Reynolds number of 4 × 106 the boundary layer transition location moved forward on the body due to the effect of the 85.5 μm particles for all heating conditions. The largest percentage changes in transition location from “clean” water, were observed for 85.5 μm particles seeded water.
Transition measurements made with varied concentrations of background particulates indicated that the effect of the 85.5 μm particles on the transition of the model reached a plateau between 2.65 particulates/ml concentration and 4.2 particles/ml. Measurements made with 123.3 μm particles at concentrations up to 0.3 part/ml indicated no similar plateau.
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Ladd, D.M., Hendricks, E.W. The effect of background particulates on the delayed transition of a heated 9:1 ellipsoid. Experiments in Fluids 3, 113–119 (1985). https://doi.org/10.1007/BF00276718
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DOI: https://doi.org/10.1007/BF00276718