Numerical Study on Flow Characteristics of Synthetic Jets with Rectangular and Circular Exits

Abstract

Flow characteristics of synthetic jets have been computationally investigated for different exit configurations under a cross flow condition. The exit configuration of a synthetic jet substantially affects the process of vortex generation and evolution, which eventually determines the mechanism of jet momentum transport. Two types of exit configurations were considered: one is a conventional rectangular exit, and the other is a series of circular holes. The interactions of synthetic jets with a free stream were performed by analyzing the vortical structure characteristics. The effectiveness of flow control was evaluated by examining the behavior of the wall shear stress. It was observed that the circular exit provides better performance than the rectangular exit in terms of sustainable vortical structure and flow control capability. In order to obtain an optimal shape of a multiple serial circular exits, comparative studies were then conducted according to hole gap and hole diameter. Detailed computations revealed that the hole gap yields a much more significant effect on flow characteristics than the hole diameter, which turned out to be relatively minor. Based on the initial strength and persistency of jet vortices, the circular exit with a suitable hole gap formed critical jet vortices that benefically affected separation control. This indicates that the flow control performance of circular exit array could be remarkably improved by applying a suitable dimensionless hole parameter. NomenclatureA jet = suction or blowing amplitude, instantaneous peak velocity at orifice h = slot width f = frequency of periodic excitation U = velocity d = boundary-layer thickness x = streamwise distance y = spanwise distance from centerline z = normal distance from wall G = gap of multiple serial circular exit D = diameter of circular exit Subscripts 0 = reference value ∞ = freestram value

Application of synthetic jet arrays for flow separation control on a circular “hump” model

“…They showed that a rectangular orifice of a given exit plane area is more likely to generate a turbulent ring than the equivalent circular orifice due to a smoothing process which tries to create an axisymmetric ring from a non-axisymmetric slug of fluid. Kim et al (2012), studied the generation and evolution of synthetic jets emitting from circular and rectangular exits in the direction normal to the surface. They found that circular exits have better performance than rectangular exits in terms of flow control ability and sustainable vortical structures.…”