Stereoscopic Particle Image Velocimetry is used for measuring the distributions of the deterministic stresses, in the tip and mid-span regions, within the second stage rotor-stator gap of a two-stage axial turbomachine. This effort extends our previous two-dimensional measurements to study the dynamics of deterministic stresses in a multistage turbomachine using experimental data. All three components of the velocity vector, and all six components of both the turbulent and deterministic stress tensors are obtained at a Reynolds number of 370,000 based on the tip speed and the rotor blade chord, and in an optically unobstructed facility that uses blades and fluid with matched optical indices of refraction. Results at 50% show that although the radial velocity levels are about an order of magnitude smaller than the axial and lateral velocity levels, the flow is not exactly two-dimensional. The wake kinking phenomenon and the presence of chopped-off stator wake segments introduce three-dimensionality to the flow. The radial velocity fluctuations are high around the kink region, and get even higher when the potential field of the stator blade starts to interact with the kink zone. In general, the turbulent normal stresses are higher than the deterministic normal stresses while the turbulent and deterministic shear stress levels are in the same order of magnitude. The flow at 90% span is dominated by the tip vortices, which create high levels of non-uniformities in the distributions of all three velocity components. The tip vortex loses its structure when it gets close to the pressure side of the following rotor blade and undergoes a possible spiral-type vortex breakdown. The meandering and convection of the tip vortices contribute to the elevated levels of average-passage turbulence and deterministic stresses along the tip vortex transport direction. The deterministic axial normal stress is higher than the turbulent axial normal stress; the deterministic lateral normal stress is initially higher, but it quickly drops down to turbulent lateral normal stress levels; and the deterministic radial normal stress is initially close to turbulent radial normal stress levels, but it decays relatively quickly and becomes less than the turbulent radial normal stress levels further downstream. The deterministic shear stress components are 5 to 10 times higher than the turbulent shear stress components.
Wake Structure of Tip Vortex Generated by a Model Rotor Blade of NACA0015 Airfoil Section
