Effective hydraulic resistance of actuator nozzle generating a periodic jet

► Effective hydraulic resistance of a nozzle increases when generating a periodically pulsating jet. ► Two mathematical models explaining the phenomena were set up. ► Experimental data lead to a law of universal validity. Because of nonlinearity of characteristics of nozzles, their effective hydraulic resistance when generating periodically pulsating jet is higher than the steady-flow value. Author investigated this effect in experiments with a nozzle supplied with superposed steady flow and a pulsation generated by piston-type pulsator, and found deviations from the predictions based on mere nonlinearity. The disagreement is explained by fluid accumulation due to its compressibility in the actuator cavity upstream from the nozzle. Two mathematical models of the periodic accumulation processes were set up. The experimental data are located between the results of these models. The final outcome of this study is a law of universal validity for design of actuators with periodic flows in nozzles.