Development of Scale-dependent Anisotropy in Isotropic Turbulence Subjected to Off-axis Rotation

Turbulent flows in rotating systems are pivotal in applications spanning from large-scale phenomena such as atmospheric and oceanic dynamics to small-scale systems such as turbomachinery. Previous experimental studies have primarily focused on the rotational effect on the mean flow and large-scale dynamics, while computational research has simulated rotational effects with multiple reference frame method. There is a lack of understanding of the rotational effect on turbulence and of turbulent models derived in the rotating (non-inertial) coordinates. Using the high-speed Particle Image Velocimetry (PIV) system measuring a zero-mean isotropic turbulent flow under different rotation conditions, the anisotropy between radial and tangential directions, induced by the presence of Coriolis force, is investigated. A rotation-induced anisotropic (RIA) subrange in a specific range of length scales is identified in the rotating conditions. With the PIV data, the lower limit of this RIA subrange is determined and a dimensionless parameter, Rotational Anisotropic Transition (RAT) number is introduced to quantify the lower limit of the RIA subrange under different rotation conditions. A generalized Taylor’s method is developed to determine the directional characteristic convection velocities and turbulent Rotation numbers to link large-scale to small-scale turbulent dynamics and provide the foundation for the development of the anisotropic turbulent model in rotating (non-inertial) coordinates.