Single component PDV measurements were conducted in the SARL on a Delta wing. The goal was to demonstrate PDV in a large low speed wind tunnel. The SARL test section is 7-feet by 10-feet, the field of view was ~ 2-feet by 1.5-feet, and the tunnel velocity was Mach 0.2.
The PDV results were compared to CFD by extracting Doppler shift in the direction of the detector from the CFD data. Note that the EFD reveals vortex structures that are smaller the CFD.
A two-component PDV system was developed and demonstrated by conducting velocity measurements in a supersonic jet with a large-scale perturbation.
The perturbation was created by focusing energy from a Nd:YAG is into the shear layer near the lip of the nozzle to create a small disturbance.
The PDV system was then employed to study the evolution of the large-scale disturbance created by the laser spot. The system was operated in two orientations, with the sheet horizontal and vertical. The phase-averaged measurement of all three components of velocity were generated 170 µs and 220 µs after the introduction of the disturbance.
At the conclusion of the Phase II SBIR program, ISSI conducted tests in the Subsonic Aerodynamics Research Laboratory (SARL) wind tunnel at the Air Vehicles Directorate of the Air Force Research Laboratory (AFRL) in collaboration with Prof. Greg Elliott of University of Illinois and Dr. Thomas Beutner, Dr. Henry Baust, Dr. Campbell Carter, and Dr. Charles Tyler of AFRL. These tests measured the flow near a wing-body junction of a UCAV model using three component PDV. Data was acquired at 5 data planes near the wing body junction. Pressure measurement using Pressure Sensitive Paint (PSP)were also conducted as part of this program. The PSP results show the expected vortex from the leading edge and the vortex from the wing body junction.
The experimental setup for the UCAV test is depicted here. The laser sheet was deployed from the top of the tunnel perpendicular to the model and the detector positions included views from the top of the tunnel, both upstream and downstream as well as an upstream side view.
Unprocessed images from the three camera pairs are shown here. The dot cards are used to align the filtered and unfiltered images from each camera pair as well as to map each processed image pair onto a single grid. Green card data is obtained at condition by tuning the laser out to a flat portion of the iodine absorption curve while seeding the tunnel. Doppler shift data is obtained with the laser tuned to the side of the Iodine absorption line. These data are processed to produce the velocity vectors shown below.
At the upstream plane, the strong vortex from the nose is seen sweeping along the side of the model. A strong secondary vortex appears at the wing-body junction. The wing-body vortex sweeps out along the wing as the main body vortex weakens. Finally, the wing-body vortex continues to sweep out along the wing as the vortex weakens.