Validation Quality Measurements and Computations of Flow in Shape Transitioning Nozzles

This paper aims to establish the groundwork for understanding the fundamental relationship between local pressure gradients, induced by local wall curvatures and shape transitioning, with nozzle performance. The overarching goal is to conduct a parametric study on three nozzles (N0, N1 and N2) with varying curvature profiles, to evaluate how these features influence flow dynamics and performance. The experimental component combines pitot-static measurements and high-speed Particle Image Velocimetry (PIV) to capture detailed flow structures. The computational approach utilizes a novel output-based mesh adaptation technique that minimizes discretization errors, which isolates modeling error during comparison with experimental measurements. This is critical for validating and identifying turbulence model limitations as well as improving Computational Fluid Dynamics (CFD) practices. CFD validation is carried out through comparison with high-speed Particle Image Velocimetry (PIV) data, focusing on streamwise velocity profiles and spanwise vorticity distributions. The simulation results capture bulk flow structures observed experimentally, as well as, boundary layer thickening, secondary vortices, and streak-like vorticity features near the wall contours. Zoomed-in profiles near the wall show strong agreement between PIV and CFD in capturing the overall boundary layer development. Performance parameters such as total pressure recovery, discharge coefficient and total pressure distortion are computed to quantify the impact of internal flow behavior on nozzle efficiency. Among the three designs, N2 exhibits the highest performance in the first two metrics, but not without the penalty of increased exit flow non-uniformity.