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Completed TRL 4 (started at 2, targeting 4)
This Tier 2 proposal continues FY20 & 21 IRAD projects. We continue development of non-intrusive two-dimensional, 3-component, time-resolved velocity and pressure measurements for the National Transonic Facility (NTF). The method tracks motion of sparsely-seeded, natural-occurring, micron-sized particles observed in the NTF. A customized code will analyze tracked particles to measure the velocity field and potentially the pressure field. In FY22, we will continue to develop this software and associated hardware while implementing a new idea for simultaneous measurement of particle size so that large, error-inducing particles can be identified and excluded from the analysis. The resulting system will produce critical data for code validation and will open new avenues for research and discovery of high-Reynolds number flows. The immediate target application is for high lift (take-off and landing) aircraft but can be applied to various aircraft and space vehicles.
Measurements of the fluid flow around a body such as a wing are critical to understanding complex fluid dynamics phenomena such as stall, flow separation, and laminar-to-turbulent transition which all affect aircraft design and performance. These phenomena contribute to the notorious difficulty of predicting the maximum lift coefficient at which aircraft operate at takeoff and landing, known as CLmax. After lift and drag, the most sought after measurement is the fluid velocity – a primary indicator of fluid behavior. The National Transonic Facility (NTF) is designed to ground test small-scale aircraft models at flight-accurate (so called “Reynolds number matched”) conditions. In the NTF, off-body velocity measurements are currently limited to 1) physical probes (pitot-static probes and hotwires) which are hard to move and which disturb the flow that is being measured and 2) a new low-TRL experimental 1D (line) imaging technique known as FLEET (femtosecond laser electronic excitation and tagging). These techniques cannot measure 2D multi-component velocity distributions required to understand the fluid dynamics of flow separation over the surface of a wing. The proposed capability can provide time-resolved (movie like) 2D images of 2 or 3 velocity components and pressure in the spatial scales and measurement locations required to assist computational fluid dynamics (CFD) developers by providing detailed code validation data (including Reynolds stress terms) suitable for comparison with increasingly powerful mean and unsteady CFD codes. Future applications of this technology will broadly benefit the measurement capabilities at the NTF and CFD validation efforts, enabling the simulation and ground-testing of more energy-efficient civilian aircraft designs. If computational codes were validated and able to accurately predict the critical value of CLmax there would be a significant reduction (hundreds of millions of dollars) in flight certification costs for US aircraft manufacturers according to Boeing. Other NASA programs testing in the NTF, such as SLS, Orion, and future missions, would benefit from this effort. Furthermore, testing of new concepts like tail-cone thrusters, and the transonic truss-braced wing as a part of the ARMD test programs would benefit from this measurement capability.
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