Modeling Pulsed-Blowing Systems for Flow Control

Abstract

A linear model for analyzing the performance of pulsed-blowing actuator systems commonly used in many flow-control applications is presented and compared with experiments. The pulsed-blowing system consists of a regulated air supply, an oscillatory valve, transmission tubing, and an actuator. The elements of the actuator are a cavity and slot at the location in the flow to be controlled. The typical design objective is to achieve the largest possible velocity-fluctuation levels at the actuator-slot exit for a given fluctuating pressure input. However, the performance of the system is strongly dependent on component geometry, flow rate, and frequency of pulsation. Lumped-element models are useful for estimating the performance of the actuator cavity and slot, but fail to account for the effects of the transmission tubing. A distributed model for the tubing combined with a lumped-element model for the actuator provides estimates of the system resonant frequencies and amplitudes. Comparisons with experiments are made for a wide range of tubing lengths, slot widths, mean flow velocities, and forcing frequencies. The resonances of the pulsed blowing system and the changes in resonant behavior are characterized by considering the reflection coefficient of the system. Unexpected behavior such as reversed flow at the slot exit and reduced fluctuation levels with increasing pressure are demonstrated and explained with the system model.