Water Tunnel Rotor Testing With Post Processing Based on PIV Measurements

Experimental investigation is required to obtain the non-dimensional coefficients that characterize the performance of new wind turbines and marine energy extracting devices, such as tidal turbines. However, data acquired from scaled models tested in tunnel facilities suffers from wall blockage and therefore, corrections must be applied to properly predict the performance of the full-sized rotor. Analytical expressions based on the axial momentum theory and correlating thrust coefficient to an equivalent free stream velocity have traditionally been used to correct power coefficients obtained experimentally. For small models, accurate force measurement is very difficult requiring a new post processing methodology when thrust data is not available. A methodology is presented in this paper that uses the velocity field data at the rotor plane, obtained from PIV measurements and CFD simulations, to account for blockage without the requirement for thrust data. A correction curve correlating axial induction factor and power coefficient is obtained and will be utilized for correction in future experiment testing.

The Effect of Inlet Guide Vanes Wake Impingement on the Flow Structure and Turbulence Around a Rotor Blade

The flow structure and turbulence around the leading and trailing edges of a rotor blade operating downstream of a row of inlet guide vanes (IGV) are investigated experimentally. Particle image velocimetry (PIV) measurements are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. Data obtained at several rotor blade phases focus on modification to the flow structure and turbulence in the IGV wake as it propagates along the blade. The phase-averaged velocity distributions demonstrate that wake impingement significantly modifies the wall-parallel velocity component and its gradients along the blade. Due to spatially non-uniform velocity distribution, especially on the suction side, the wake deforms while propagating along the blade, expanding near the leading edge and shrinking near the trailing edge. While being exposed to the nonuniform strain field within the rotor passage, the turbulence within the IGV wake becomes spatially nonuniform and highly anisotropic. Several mechanisms, which are consistent with rapid distortion theory (RDT) and distribution of turbulence production rate, contribute to the observed trends. For example, streamwise (in rotor frame reference) diffusion in the aft part of the rotor passage enhances the streamwise fluctuations. Compression also enhances the turbulence production very near the leading edge. However, along the suction side, rapid changes to the direction of compression and extension cause negative production. The so-called wall blockage effect reduces the wall-normal component.

The Effect of IGV Wake Impingement on the Flow Structure and Turbulence Around a Rotor Blade

The flow structure and turbulence around the leading and trailing edges of a rotor blade operating downstream of a row of Inlet Guide Vanes (IGV) are investigated experimentally. Particle Image Velocimetry (PIV) measurements are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. Data obtained at several rotor blade phases focus on modification to the flow structure and turbulence in the IGV wake as it propagates along the blade. The phase-averaged velocity distributions demonstrate that wake impingement significantly modifies the wall-parallel velocity component and its gradients along the blade. Due to spatially non-uniform velocity distribution, especially on the suction side, the wake deforms while propagating along the blade, expanding near the leading edge and shrinking near the trailing edge. While being exposed to the non-uniform strain field within the rotor passage, the turbulence within the IGV wake becomes spatially non-uniform and highly anisotropic. Several mechanisms, which are consistent with rapid distortion theory (RDT) and distribution of turbulence production rate, contribute to the observed trends. For example, streamwise (in rotor frame reference) diffusion in the aft part of the rotor passage enhances the streamwise fluctuations. Compression also enhances the turbulence production very near the leading edge. However, along the suction side, rapid changes to the direction of compression and extension cause negative production. The so-called wall blockage effect reduces the wall-normal component.