Laminar flow performance of a heated body in particle-laden water

Abstract

The effects of small uniformly sized spherical particles seeded into the freestream flow of a water tunnel on the delayed transition of a heated 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 arc length and the approach flow velocity decreases monotonically with increasing d/δ*, where d is the particle diameter and δ* is the displacement thickness at a critical location. The location of initial turbulent spot formation defines the critical location, and, within the range of experimental conditions reported here, is independent of particle size, heating condition and the approach velocity. For the high unit Reynolds numbers considered (Reu⩽ 1.88 × 107 per metre), there is no observed critical particle diameterbased Reynolds number threshold; all sizes of particles considered in the experiments (d = 37 to 218 μm) have some effect on transition. In a second set of experiments, particles were injected into the laminar boundary layer from a small orifice located at the forward stagnation point. These injected particles have no observable effect on the laminar layer or transition, which suggests that the injected particles fail to produce wakes or vorticity within the laminar layer that may lead to turbulent spot production.