Numerical Investigation of Jet and Vortex Actuator (JaVA) for Active Flow Control

Abstract

An oscillatory, zero-net-mass flux Jet and Vortex A ctuator (JaVA) was modelled as part of a flat plate and simulated in a boundary layer f low. JaVA is an active flow control device that can be used for flow separation control and th us can delay boundary layer transition. It has been already shown experimentally that JaVA induced flow types in still water include angled and vertical jets, wall jets and vortex flow s and that they highly depend on governing parameters such as the frequency and amplitude of the actuator and the mean position of the actuator plate. In this study, a commercial uns teady, incompressible Navier-Stokes solver (Fluent) has been used to study the flow fie lds generated by JaVA in a water channel. The detailed quantitative information about the performance of JaVA on a flat plate boundary layer is obtained numerically. The results are validated by visualization experiments with the similar CFD set up. The numerical results show vortex like structures emerging from actuator’s wide gap with a size that matches the experimentally observed vortex. It has been found that the emerging vortice s move along the flat plate surface usually merging with each other downstream of the boundary layer. In addition to governing JaVA parameters in still water (the jet Reynolds number, the scaled amplitude, the mean position of the actuator), the characteristics of boundary l ayer flow are important for the JaVA performance in channel flow. These include the magnitude of the free stream velocity and the boundary layer profile (e.g. laminar or turbule nt). In this study, we consider an approximation to the Blasius profile (a 4 th -order polynomial profile). To account the free stream velocity, a new dimensionless parameter (r) is introduced which is the ratio of average jet velocity “ Vj= 2abf/ ww” to free stream velocity “ U�” ( r = V j/ U �). Our numerical results clearly show that JaVA, when mounted in a f lat plate laminar boundary layer, affects boundary layer profile considerably. That is, JaVA induced boundary layer profiles are clearly more resistant to the flow separation. The effects of JaVA with different operation regimes on the various boundary layer flow characteristics such as the displacement thickness, the momentum thickness, the energy thickness and the friction coefficient are reported. This computational study can be utilized to steer the governing parameters effectively for an improved actuator design.