LAMINAR-FLOW PERFORMANCE OF A HEATED BODY IN PARTICLE-LADEN WATER

The effects of small uniformly sized spherical particles seeded into t he freestream flow of a water tunnel on the delayed transition of a he ated laminar flow control body is examined experimentally. In separate trials, four different mean diameter particle seedings were added to the flow and the approach flow velocity was cycled from subcritical to supercritical conditions at three different body heating conditions. The transition Reynolds number based on the body are length and the ap proach flow velocity decreases monotonically with increasing d/delta, where d is the particle diameter and delta is the displacement thick ness at a critical location. The location of initial turbulent spot fo rmation defines the critical location, and, within the range of experi mental conditions reported here, is independent of particle size, heat ing condition and the approach velocity. For the high unit Reynolds nu mbers considered (Re-u less than or equal to 1.88 x 10(7) per metre), there is no observed critical particle diameter-based Reynolds number threshold; all sizes of particles considered in the experiments (d = 3 7 to 218 mu m) have some effect on transition. In a second set of expe riments, particles were injected into the laminar boundary layer from a small orifice located at the forward stagnation point. These injecte d particles have no observable effect on the laminar layer or transiti on, which suggests that the injected particles fail to produce wakes o r vorticity within the laminar layer that may lead to turbulent spot p roduction.