Interest in abating noise pollution from future eVTOL vehicles utilized in urban environments is a major motivating factor for this proposed study. Past strategies for predicting noise about aircraft and rotorcraft tended to be highly empirical leading to limited generalization and accuracy. On the other hand, modern acoustics methodologies can be employed as an effective and comprehensive means of predicting noise only if supplied with critical information about the transient turbulent flow surrounding the vehicle. The options for obtaining accurate information about the transient behavior of turbulent aerodynamic flows are significantly limited and remain as an obstacle to the modeling of acoustic fields. This difficulty is exacerbated by the complex, turbulent flow field surrounding multi-rotor configurations such as proposed by over 300 listed eVTOL design teams. The focus of this phase I STTR proposal is in demonstrating the unique capabilities of our breakthrough Vorcat technology in turbulent flow prediction via a grid-free vortex method that addresses the problem of reliably analyzing acoustic fields produced by eVTOL vehicles. This project will compute the flow past a stacked rotor concept in hover position and compare the results with physical experiments conducted at the Applied Research Laboratories at The University of Texas at Austin (ARL:UT). Analysis of the results will be aimed at understanding and explaining why changing the distance between the two co-axial rotors affects the measured noise level in a meaningful way. This will be accomplished by modeling turbulence intensities at various regions of the flow as well as resolving non-steady interactions of rotor-shed vorticity with other sources of vorticity in the flow field, and tracking of wake vortices, etc. Our Purdue University partner will assist us in all phases of this effort, including the selection of an appropriate CAA technology and planning of the next phases. It is expected that at the end of Phase I, the feasibility of our simulation technology will be proven, laying the ground work for its validation and verification in Phase II. Our Phase II plan may also focus on a specific customer design that will be simulated in software and then tested for verification in the wind tunnel at ARL:UT. The ultimate goal is to construct a reliable CAA technology based on Vorcat CFD that can be employed by the eVTOL industry to reduce noise pollution by its various designs.
