A CFD analysis of the flow over a side-supported sphere with localised synthetic jet

摘要

The application of synthetic jet in a cross flow has been studied numerically in mostly two-dimensional configurations. The synthetic jet is becoming a useful technological tool for flow control. For aerodynamic applications this would be beneficial in reducing fuel consumption by increasing the efficiency of the flow over solid geometries. The present numerical simulation is conducted on a three-dimensional bluff body, a side-supported sphere, in a cross flow. The computational model was constructed based upon the experimental work conducted by the authors [6,16]. The synthetic jet was modelled numerically based upon the harmonic sinusoidal motion of the actuator used in the physical experiments. An open type boundary condition was used in the ANSYS CFX commercial CFD package that has not been previously developed using this software to produce the zero net mass flow condition whilst generating the required velocity profile. The synthetic jet asymmetrical and localised, was located at three different angles of incidence 6.5°, 76° and 100°. The cross flow was set at the Reynolds number of 5 × 10~4. Since the flow over the side-supported sphere at this Reynolds number is unsteady and the synthetic jet is inherently an oscillating turbulent shear flow it was required to conduct a transient CFD analysis. Two different turbulence models were used to predict separation of the unsteady flow field with the SST turbulence model proving to be most accurate when compared to the experimental data. It was found that the synthetic jet at all angles of incidence improved the surface pressure distribution before separation relative to the baseline case. Post separation the localised synthetic jet increased the crosswise vorticity in the wake region at 6.5°. With the synthetic jet at 76° and 100° produced a similar result by decreasing the size of the wake and streamlining the flow through a breaking up crosswise vorticity in the wake region. Further the interference flow at the support-sphere junction was streamlined leading to a slight decrease in the drag.