Gerben Kooijman

Finite difference time domain electroacoustic model for synthetic jet actuators including nonlinear flow resistance

A lumped element electroacoustic model for a synthetic jet actuator is presented. The model includes the nonlinear flow resistance associated with flow separation and employs a finite difference scheme in the time domain. As opposed to more common analytical frequency domain electroacoustic models, in which the nonlinear resistance can only be considered as a constant, it allows the calculation of higher harmonics, i.e., distortion components, generated as a result of this nonlinear resistance. Model calculations for the time-averaged momentum flux of the synthetic jet as well as the radiated sound power spectrum are compared to experimental results for various configurations. It is shown that a significantly improved prediction of the momentum flux-and thus flow velocity-of the jet is obtained when including the nonlinear resistance. Here, the current model performs slightly better than an analytical model. For the power spectrum of radiated sound, a reasonable agreement is obtained when assuming a plausible slight asymmetry in the nonlinear resistance. However, results suggest that loudspeaker nonlinearities play a significant role as well in the generation of the first few higher harmonics.

Synthetic Jet cooling using asymmetric acoustic dipoles

In two earlier papers [1, 2] the principles and experimental results have been discussed for a typical embodiment of synthetic jet cooling technology: an acoustic dipole cooler comprised of a standard loudspeaker in a housing provided with two pipes. The current paper shows experimental and numerical results for another type: the asymmetric dipole. Basically, this type consists of a loudspeaker with a minimal volume attached to it with one or more holes with or without pipes. Results for driving power and noise are presented for a number of actuators covering a large parameter space: frequency, pipe dimensions and driving voltage were varied over a large range. A relatively simple acoustic model extended to include separation losses matched the experimental results very well. The results indicate promising heat transfer performance with minimal noise combined with a large degree of freedom.