Browsing by Author "Rist, Ulrich (Apl. Prof. Dr.-Ing.)"

Now showing 1 - 1 of 1

Open Access
CFD simulation of Jet and Vortex Actuators (JaVA) with and without cross flow boundary layer
(2010) Rashad, Muhammad Aqeel; Rist, Ulrich (Apl. Prof. Dr.-Ing.)
In the present study an active flow control actuator is studied numerically. This type of actuator was first studied experimentally by Lachowicz et al. and called “Jet and Vortex Actuator” (JaVA). This kind of active flow control actuator produces different flow fields depending upon the frequency and the scaled amplitude of the imposed oscillation. Thus, it can be used to produce different net reactions, like vertical jets, wall jets, or a vortex flow. The actuator under consideration consists of a cavity and a rigid plate which serves as the actuation surface. The actuator plate acts like a piston pumping air out of the cavity on the down stroke and sucking air into the cavity on the upstroke. Different cases are selected for validation of the simulations. Our simulations yield the unsteady flow field, whereas only time-averaged data are available from literature. Thus, our simulations provide extra details of the flows through the gaps intended for a better understanding of the actuator flow. Qualitative and quantitative comparisons of the time-averaged data with the experiments are very encouraging. Especially, the different flow regimes appear for the same parameters as in the experiments. Different parameters like cavity depth and plate position relative to the cavity upper wall and compressibility effects are also studied. In the present work we also presented a modified design in order to improve and understand flow mechanisms. In this new design the horizontal plate is stationary and a vertical plate inside the cavity moves left and right to push fluid through the narrow and wide gap alternatively. Interestingly, in this new design like in the original, once again we get different flow modes like vertical jet, angled jet, vortex and wall jet but from the narrow gap. Different parameters like cavity depth and gap widths and plate position relative to the cavity upper wall are also studied. Relations between different nondimensional parameters like Reynolds number, Stokes number, Strouhal number and scaled amplitude and their effect upon the flow field are also presented in detail. In the present work 3D results are also presented for the modified design. It was found that strong 3D end effects are present. The flow field is completely different for 2D and 3D simulations. For the same set of parameters in 2D we get a very nice vortex as where in 3D we get a vertical jet. We also presented results with a cross-flow boundary layer for 2D cases of original and modified design with different orientations of gaps with respect to the cross-flow. It was found that configuration-2 in the original design in which the narrow gap comes first to the cross flow and the wide gap later, is more effective with respect to increasing the flow momentum close to the wall and in controlling the boundary layer. For the 3D modified design with the cross flow boundary layer two different gap orientations with respect to the oncoming flow are used. In the first configuration the gaps are oriented across the flow with the wide gap coming first and the narrow later. In the second configuration the gaps are oriented along the boundary layer. In the 3D case this second configuration turns out to be the most effective with respect to increasing the flow momentum close to the wall, such that this kind of actuator can be used for boundary layer (separation) control. For the present investigations the commercial CFD-software FLUENT is used for flow calculation and visualization. The accompanying grid-generation software GAMBIT is used for geometry specification and grid generation.