Prandtl-D Flying Wing Aerodynamic Characterization and Flow Survey

NASA Prandtl-D is a flying wing that exhibits several novel aerodynamic behaviors. The wing is designed based on Prandtl’s theory of Bell-Shaped Lift Distribution (BSLD), i.e., a minimum induced drag solution, with suspected assistive yaw effect called proverse yaw. Flight test data from Bowers et al. (2016, 2021) and computational studies from Yoo (2018) have provided evidence of downwash reversal along with the induced thrust effect near wing tip. Aerodynamic performance characterization is performed at the San Diego State University Low-Speed Wind Tunnel to verify these effects using conventional force balance measurement, surface oil visualization, and Particle Image Velocimetry (PIV) measurement across the wingspan. Preliminary results of the aerodynamic force measurement of the Prandtl-D wing show good agreement with the computational study, exhibiting similar results on lift, drag and pitching moment performance. Surface oil visualization results show similarity to computational streamline simulation along with expected stall progression with even flow distribution. PIV measurement is being performed with the goal of obtaining the aerodynamic pressure loading across the wingspan from velocimetry flow results. The pressure gradient distributions can be obtained through Reynolds Averaged Navier Stokes (RANS) equation, which can then be further reconstructed to obtain the pressure distribution over the entire wing, thus verifying the hypothesis of induced thrust near wing tip.