PIV experimental study on the turbulence characteristics of a semi-confined impinging jet issuing from a circular pipe
摘要
Impinging jets are widely recognized for their efficiency in mass, momentum, and energy transfer, making them essential in various engineering domains, including hydraulic engineering, thermal systems, and industrial cleaning technologies. In many practical applications, jet flows are constrained by spatial limitations, leading to the formation of semi-confined impinging jets. These jets feature a semi-confined plate positioned parallel to the impingement surface at the nozzle exit, generating a more complex flow structure and significantly modifying turbulence behavior. This study experimentally examines the turbulence characteristics of a semi-confined impinging jet produced by a circular pipe using two-dimensional particle image velocimetry (2D-PIV). Experiments are conducted for four impingement distances (H = 3d, 4d, 5d, and 6d), where H denotes the distance between the nozzle exit and the impingement plate, and d is the nozzle diameter. The inlet Reynolds number, based on nozzle diameter and bulk jet velocity, is maintained at a constant value of 11,052. Instantaneous velocity fields are captured along the jet center plane to investigate the streamwise development of turbulent kinetic energy, probability density functions (PDFs) of fluctuating velocity, skewness and flatness factors, and two-point correlation functions. The results reveal that, with increasing impingement distance, both the peak turbulent kinetic energy and the spatial extent of the high-turbulent-kinetic-energy region in the free jet shear layer grow markedly. In contrast, the peak turbulent kinetic energy in the wall jet region initially rises and then diminishes as the impingement distance increases further. Notably, when H ≤ 4d, the peak turbulent kinetic energy in the wall jet region exceeds that in the free jet region, whereas for H ≥ 5d, the free jet region displays higher peak values. The local peak turbulent kinetic energy in the wall jet region exhibits exponential decay in the radia