Design, Characterization, and Verification of a Closed Loop Wind Tunnel With Linear Cascade and Upstream Wake Generator

A new cascade wind tunnel has been designed and constructed at the LSU Wind Tunnel Laboratory. The objective was to develop a versatile test facility, suitable for a wide range of experimental studies and measurements on turbine airfoils, especially with regards to film-cooling incorporating realistic unsteady effects due to passing wakes. The test section consists of a four passage linear cascade composed of three full blades and two shaped wall blades. The 2D blade shape profile of the cascade is a high-lift, low-pressure turbine L1A profile provided by the US Air Force Research Laboratories (AFRL), with a 152-mm axial chord. The Reynolds number based on the axial chord length at the nominal freestream velocity of 50 ms⁻¹ is 500,000. A conveyor-based system was designed and fabricated to simulate the passing wakes of the upstream vanes (or blades) on the test blades (or vanes) depending on which airfoil types are put on the stationary frame and the moving frame of the conveyor. The original implementation uses blade profiles on the stationary frame and thick plate wake generators on the translating frame. Results are presented from hot-wire surveys conducted to characterize and qualify the velocity and turbulence intensity distributions and associated spectral characteristics at the cascade test section inlet, in the wake of the vanes and in the wake of the test blade. A blade instrumented with 123 pressure taps was used to acquire static pressure profiles of the cascade central blade, which were compared to the ones from the nominal airfoil design as well as to those obtained from a CFD simulation of the cascade flow. Incoming velocity and temperature profiles were found to be uniform to within a few percentage points, and the pressure coefficient distribution was found to be in good agreement with design values. The passage periodicity of the conveyor-belt-driven, flat-plates was verified and their wake was characterized. These results verified that the cascade wind tunnel operates according to design, thus proving to be a reliable test-bed for film cooling studies with and without unsteady wake effects. The design also incorporates an in-house-designed, miniature periscopic and adjustable laser sheet generating system integrated within the “dummy” blades to enable Particle Image Velocimetry measurements in the intra-blade domain.