THE EFFECTS OF IGV WAKE IMPINGEMENT ON THE BOUNDARY LAYER AND THE NEAR-WAKE OF A ROTOR BLADE

摘要

This paper examines the response of a rotor blade boundary layer and a rotor near-wake to an impinging wake of an Inlet Guide Vane (IGV) located upstream of the rotor blade. Two-dimensional Particle Image Velocimetry (PIV) measurements are performed in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. Data obtained at several rotor phases enables us to examine IGV-wake-induced changes to the structure of the boundary layer and how these changes affect the flow and turbulence within the rotor near-wake. We focus on the suction surface boundary layer, near the blade trailing edge, but analyze the evolution of both the pressure and suction sides of the near-wake. During IGV-wake impingement, the boundary layer becomes significantly thinner, with lower momentum thickness and more stable profile compared to other phases at the same location. Analysis of available terms in the integral momentum equation indicates that the phase-averaged unsteady term is the main contributor to the decrease in momentum thickness within the impinging wake. Thinning of the boundary/shear layer extends into the rotor near wake, making it narrower and increasing the phase averaged shear velocity gradients and associated turbulent kinetic energy (TKE) production rate. Consequently, the TKE increases during wake thinning, with as much as 75% phase-dependent variations in its peak magnitude. The paper introduces a new way of looking at PIV data by defining a wake oriented coordinate system which enables to study the structure of turbulence around the trailing edge in great detail.