Flow Field Characteristics and Surface Strengthening Analysis of Twin Cavitating Jets Impinging on a Concave Surface

Array-based strengthening has been applied to the strengthening of the inner surfaces of large curved structural components because of its green, efficient, and low-cost characteristics. However, as its basic unit, twin cavitating jet impact strengthening still has unclear flow field evolution and strengthening mechanisms when acting on concave surfaces. In this study, twin cavitating jets impinging on a concave surface were investigated by combining numerical simulation and experiments. A twin cavitating jet model was established to analyze the effects of nozzle spacing and concave surface curvature on the distributions of flow velocity, pressure, vapor volume fraction, and wall shear stress. Strengthening experiments on concave surfaces were then carried out to establish the internal relationship between the flow field characteristics and the surface strengthening effect of the material. The results show that the impingement behavior of twin cavitating jets on a concave surface is closely related to nozzle spacing and surface curvature. The concave curvature promotes the convergence and recirculation of the twin cavitating jets near the wall, making the cavitation clouds more likely to collapse synchronously in the near-wall region and thereby enhancing cavitation intensity. At a nozzle spacing of 30 mm and a concave surface curvature of K = 1/65 mm−1, the surface hardness of Q235 low-carbon steel increased from 115 HV to 189 HV, corresponding to an increase of 64.3%. The hardened layer depth reached 200 μm, accompanied by significant plastic deformation.