Near-Field Velocity Measurement System for Wind Tunnel Testing

Applied University Research, Inc. (AUR) is proposing to develop a state-of-the-art prototype wind velocity vector instrument for measuring the near-field flow of models under test in large-scale high-speed wind tunnels. The instrument under consideration is based upon laser-Doppler velocimetry (LDV), but with modifications to enable sub-miniaturization of the laser-emitting probe head and that leverage the use of recently-developed advanced photonics components. A Phase I study which preceded this proposal examined the feasibility of the technique for the proposed application. It was shown using structural and optical analyses that the concept of employing thin, formed windows is a robust and cost-effective solution for providing optical access through wind tunnel models. The results from the Phase I tests and analyses led to the conclusion that the proposed instrument is feasible for prototype development and deployment in large scale wind tunnel facilities--the subject of the currently proposed project. The highlight of the proposed work is the delivery and demonstration of a fully-operational subminiature LDV probe with robust support photonics and controls that require very little user adjustment for day-to-day operation. BENEFIT: An array of customers may benefit from the improved flow sensing capabilities of the sub-miniature laser-Doppler velocimeter (SMLDV). The product would provide advanced testing capabilities for an important US aerospace facility, the Arnold Engineering Development Center 16ft Transonic Wind Tunnel, for obtaining crucial information about the highly dynamic flow the occurs near bodies in flows. Additional facilities of importance within the US such as the National Transonic Facility located at the NASA Langley Research Center and the 11ftx11ft Transonic Wind Tunnel at the NASA Ames Research Center would also benefit from the capability to measure flow velocity vectors using a probe mounted within wind tunnel test models. The probe and support hardware are robustly-designed and operate within difficult environments which may include large fluctuations in temperature or pressure. The feature of robustness opens the possibility for in situ measurements within jet engines or mounted in test aircraft to obtain external flow profilesat real-world flow scales that are of interest to engineers. In addition to aerospace applications, the automotive industry has many complex internal and external flows that a turn-key high resolution measurement system could address, such as the performance of window defrosting systems and cabin noise.