Part I: A Novel Compact Water Tunnel. Part II: Evolution of Delta Wing Surface Contour from Flat Plates to Boxfish at Low Reynolds Numbers

This thesis is presented in two parts. Part I (Chapters 1–2) addresses a common challenge for experimentalists: the scarcity of laboratory space. Inspired by recent advances in fan-array wind tunnels, a novel, ultra-compact water tunnel was developed that uses an array of submerged thrusters to drive flow within a rectangular tank. Prioritizing space efficiency over power efficiency, the design achieves flow quality comparable to traditional facilities while occupying just 8% of the typical footprint. Flow characterization using particle image velocimetry (PIV), hot-film anemometry, and laser Doppler velocimetry (LDV) demonstrates the tunnel’s effectiveness and suitability for fluid dynamic research. Part II (Chapters 3–5) uses this new facility to investigate the aerodynamics of delta wings with extreme leeward surface contours in low Reynolds number subsonic flow. While the canonical delta wing flow field is dominated by a pair of counter-rotating leading-edge vortices (LEVs), similar vortex structures have been observed over a range of geometries—including biological forms such as boxfish. However, the influence of non-uniform thickness and large leeward surface deformations on LEV behavior remains poorly understood. To address this, a family of 70° sweep delta wing shapes was defined using Bézier splines, spanning a continuum from flat plates to forms approaching bluff bodies. Eight 3D-printed wing models were fabricated, with systematic variation in cross-sectional curvature and thickness, including a conical apex section with a thickness-to-span ratio of 0.5. Dye visualization, stereoscopic PIV (SPIV), and load cell measurements were used to examine LEV strength, position, and wing performance across multiple angles of attack. Results show that increasing the leeward surface height, effectively confining the LEV, leads to substantial reductions in vortex strength and shifts in vortex position. Experimental evidence of a dual primary vortex structure over thick delta wings is reported for the first time. Tomographic dye reconstructions reveal complex three-dimensional vortex behavior in the aft section of the wings, including flow separation patterns reminiscent of those seen in hatchbacks and Ahmed bodies. Force measurements reflect the observed flow field, with highly non-linear force evolution with angle of attack depending on model cross-sectional and longitudinal profiles. These findings provide new insight into the interplay between surface shape and vortex structure, and further demonstrate the capabilities of the compact flow facility.