Experimental investigation of turbulent fluctuation characteristics observed at a moving point under crossflows

In this study, the flow characteristics of turbulent fluctuations observed at a moving point under crossflows are experimentally investigated. For this, an experimental system is developed in which a measuring probe is able to move across a flow field with a moderate velocity, and the velocity of the probe can be adjusted freely within a certain range. The experimental results are compared to those of Balzer’s and Cooper’s models — two spectral models commonly used in current theoretical research and practical applications relative to moving vehicles. The results indicate that the flow characteristics experienced by a moving point are different from those experienced by a stationary point. For a fixed crossflow velocity, as the velocity of the moving point increases, the turbulence integral scale of longitudinal velocity fluctuations decreases, and the longitudinal turbulence spectrum shifts toward high frequencies correspondingly. A semi-elliptic model is proposed to qualitatively estimate the turbulence integral scale measured at a moving point. The flow characteristics experienced by a moving point exhibit an apparent Doppler effect. Furthermore, the deviation of Balzer’s model is pointed out, and the dominant causes for this effect are discussed, while the accuracy of Cooper’s model is verified through an experimental approach for the first time. Additionally, it is demonstrated that the von Kármán longitudinal spectrum can also be adapted to estimate the spectrum of turbulent fluctuations observed at a moving point. This work provides more data for the current research of flow characteristics relative to moving vehicles as well as other moving objects, which could be useful for analyzing the stability of a moving object under crossflows.