Smooth Wavelength Transition In A Lorentz Force Based Actuator System For Turbulence Research

The development of robust methods to significantly reduce frictional resistance of the turbulent boundary layer involves wind tunnel experiments with transversal waves on an extended aluminum surface. For this purpose an actuation system to generate the transversal waves by phase-shifted, uniformly distributed electromagnetic actuators has been developed. Each of these actuators are mechanically coupled with the aluminum surface and driven by an FPGA. They adapt to the change of wave parameters with automatically calculated smooth signal transitions. One of these signal transitions is the developed method of smooth wavelength transition based on a direct digital synthesis (DDS). This method ensures a transition by means of an intelligent adaptation of the readout steps of a waveform look-up table and thus eases the application of special control algorithms ensuring the precision of the waveform [5].