Experimental and numerical study on the flow behind a TPS

Abstract

Particle Image Velocimetry (PIV) is a powerful tool for the non-intrusive investigation of complex flow fields. The present paper describes Stereo PIV measurements of the flow field behind a counter rotating ultrahigh-bypass fan turbine power simulator (CRUF-TPS) which have been performed at the low speed wind tunnel NWB of the German-Dutch Wind Tunnels (DNW). The experimental data was used for the validation of numerical codes using different turbulence models, as former CFD calculations suffered from the absence of a complete experimental data base. The aim of the study was the investigation of the turbulence and the shear flow mixing in the flow behind the CRUF-TPS. The experimental SPIV set-up was made up of two PCO4000 cameras (11 Megapixels) providing a very high spatial resolution, and a high power Nd-YAG double pulse laser with 380mJ per pulse output energy (λ = 532 nm). The flow was seeded with DEHS particles with a diameter of about 1 µm. In two different planes all three components of a large number of instantaneous velocity vector fields were measured in forward scattering mode for several different flow and turbine conditions. The first plane perpendicular to the main flow with an observation area of 410 x 330 mm² was located at x = 450 mm downstream of the TPS core trailing edge, the second plane was adjusted parallel to the main flow between x = 10 mm and x = 310 mm with a size of 360 x 300 mm². In both cases, the shear layers between free stream, fan flow and core flow of the TPS could be observed. In order to determine the differences between periodic and non-periodic effects of the turbulence mixing in the shear layers, the PIV measurements were triggered both at a random point of time and phase-locked to a fixed blade position of the TPS fan. For the evaluation of the PIV images an iterative multi-grid cross-correlation method with image deformation was applied with 32 x 32 pixels² final window size and a step width of 16 pixels in each direction, leading to instantaneous velocity fields with up to 43000 three-component-vectors. A number of 700 to 1000 double images were acquired per test case for reaching convergence of the averages and RMS-values. For the first PIV set-up (light sheet perpendicular to the main flow), also the x-component of the flow vorticity could be calculated.