Study on oscillating flow of moderate kinetic Reynolds numbers using complex velocity model and phase Doppler anemometer

Oscillating flows have fundamental effects on the heat and mass transfer of Stirling engines and gas springs. A complex velocity model was proposed to describe the fully-developed laminar oscillating flow through introducing complex functions and simplified control equations. The maximum dimensionless velocity decreased and the smooth core area of velocity expanded as the kinetic Reynolds number increased, which led the Stokes layer became thinner. Experiments were carried out in an apparatus consisting of piston-cylinder space connected to a straight duct. Instantaneous velocities of oscillating flows for Reω value of 230, 900 and 1800 were measured by a phase Doppler anemometer (PDA), where the effects of responding time, accuracy and features of tracer particles were analyzed. The experiments indicated that the complex velocity model with Reω was suitable to describe the fully-developed laminar oscillating flow, and the average deviation was about 10%. For a moderate-value Reω, the ratios of maximum dimensionless velocity for r = 0.85 R to r = 0 R were 1.06-1.10, which were evidences of “annular effect”.