Technical Abstract: To support the eVTOL industry and quiet propulsion efforts within the Air Force and the DoD in general, Techsburg will lead a team to develop and mature a low-noise propeller design suitable for near-term commercial use across a range of sizes and thrust classes.
Overview: During this Phase I, show feasibility to provide a mature, certified, commercial off-the-shelf family of scalable low-noise propellers for eVTOL airframe companies and the Air Force Agility Prime program and USAF Propulsion Directorate.
Technical Merit: Following a decade of low-noise propulsion research, acoustic design tool development, and experimental validation of both basic and advanced propulsion concepts for both forward and hovering flight, Techsburg will design a family of quiet and efficient propellers based on an optimal combination of performance and high-TRL features.
Team: Techsburg – Advanced modeling (PowerFLOW, CHARM, CFD, FEA, custom tools, Industrial DoD suppliers and propeller OEMs)
AVEC – World class expertise in acoustic modeling, measurements, and data reduction
Virginia Tech Aerospace and Ocean Engineering – Deep expertise in propulsion aeroacoustics and measurement techniques
Commercialization: Provide technically mature propeller hardware to eVTOL aircraft clients, DoD suppliers, and DoD programs by partnering with Rotating Composite Technologies during Phase II and beyond.
Topic focus areas addressed: Novel acoustic techniques, Advanced aircraft manufacturing, Aircraft design and analysis tools
An experimental investigation of the effect of inlet flow conditions and improved geometries on the performance of modern axial exhaust diffusers of gas turbines has been completed. As the first of a two-part series, this article concentrates on characterizing diffuser sensitivity to parametric variations in internal geometry and inlet flow conditions. Full-factorial experiments were carried out on five parameters including the inlet Mach distribution, shape of the support struts, shape of the oil-drain strut, diffuser hade angle, and the hubcap configuration. To enable an efficient sweep of the design space, experiments were performed in this initial study at a down-scaled turbine exit Reynolds number (Re_H roughly 3% of the value for an H-class diffuser) and at a full-scale turbine exit Mach number. The study was accomplished in a continuous, cold-flow wind tunnel circuit, and tailored distributions of Mach number, swirl velocity, and radial velocity derived from on-design conditions of an industry diffuser were generated. Measurements included 5-hole probe traverses at planes of interest. Diffuser performance was most sensitive to the inlet Mach distribution with losses of 0.081 points of pressure recovery due to a non-uniform Mach distribution with higher velocity near the hub versus a uniform one. Detailed comparisons of axial flow variation for a top-performing configuration versus related configurations shed physical insight regarding the evolution of kinetic energy distortion into viscous loss in the wake, as well as highlight the benefit of uniform inlet profiles in practice despite the lower theoretical recovery of such cases. The results presented here isolate the inlet flow distribution as a parameter of high interest for further study which is carried out for both on- and off-design conditions in the companion article soon to be published.