Modal Decomposition of Synthetic Jet Flow Based on CFD Computation

Tomáš Hyhlík,Hana Netřebská

doi:10.1051/epjconf/20159202026

Tomáš Hyhlík, Hana Netřebská

Open Access

https://doi.org/10.1051/epjconf/20159202026

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Abstract

The article analyzes results of numerical simulation of synthetic jet flow using modal decomposition. The analyzes are based on the numerical simulation of axisymmetric unsteady laminar flow obtained using ANSYS Fluent CFD code. Three typical laminar regimes are compared from the point of view of modal decomposition. The first regime is without synthetic jet creation with Reynolds number Re = 76 and Stokes number S = 19.7. The second studied regime is defined by Re = 145 and S = 19.7. The third regime of synthetic jet work is regime with Re = 329 and S = 19.7. Modal decomposition of obtained flow fields is done using proper orthogonal decomposition (POD) where energetically most important modes are identified. The structure of POD modes is discussed together with classical approach based on phase averaged velocities.

Highlights

Synthetic jet is zero net mass flux device, it means that there is no mass flux to its surroundings
It is necessary to mention that temporal amplitude corresponding to first proper orthogonal decomposition (POD) mode depicted in the figure 4 is almost constant negative function and it flows in the opposite direction is drawn
It has been observed that POD modes number six and seven are connected with three times higher frequency and more finer spatial structure and similar behaviour is observed for higher POD modes with decreasing amount of energy included in the modes

Summary

Introduction

Synthetic jet is zero net mass flux device, it means that there is no mass flux to its surroundings. There is only momentum transfer to the surroundings of synthetic jet. The possibility to generate (synthetize) jet is connected with irreversibility. Positive entropy production is leading to vorticity flux from the orifice in the blowing part of the oscillation period. If there is enough vorticity flux vortex ring can be observed in the flow field. The created vortex ring is inducing velocity in the direction outside from the orifice. Synthetic jet can be generated only in the case where vortex ring induced velocity is able to overcome suction velocity. Velocity scale is defined as time averaged blowing orifice centerline velocity over an entire cycle. Where TE is blowing time and T = 1/ f is oscillation period. Velocity scale can be defined as time and spatial averaged blowing orifice velocity.

Existence of Synthetic Jet

Results

Conclusions