Supersonic Microjet Actuators for Control Of Cavity Flows
Air traveling over a cavity creates an unsteady flow field. This is especially true in the case of aircraft - which travel at high speeds and varying conditions. Such cavities include landing gear wheel wells and internal weapons bays. When these cavities are exposed, a highly unsteady air flow passes over the cavities resulting in high dynamic pressures and acoustic loads in cavities and within the vicinity of the cavities. Such loading results in decreased and less stable flight dynamics of the aircraft as well as increased noise within the aircraft. Additionally, the unsteady airflow acts on the stores released from the cavities resulting in decreased delivery accuracy in the case of a weapons payload. Furthermore, the high dynamic loads in and around the cavity results, over time, in structural fatigue at the areas of the high loads. In order to increase the stability of air flow over aircraft cavities, and thus reduce the high pressure loading, various methods have been proposed.
Most techniques presently used are/have been passive and their performance is either marginal or not uniform over a desired range of operating conditions. Such control techniques either require too much power/flow rate and/or often adversely affect system performance when flow control is not needed, factors which make them undesirable for practical applications.
The proposed supersonic microjets enable active control of cavity flows with minimal flow requirements which produces substantial performance gains in terms of reducing the high dynamic pressures and acoustic loads in flows over cavities. The scalability, simplicity, adaptability, and minimal flow requirements and its demonstrated efficacy makes this technique a strong candidate for implementation in aircraft.
Fluidic actuators, consisting of arrays of supersonic microjets have been used to actively control and manipulate the highly unsteady flow over cavities. The microjet arrays produce supersonic flow streams that have very high momentum while requiring very low mass flow rates and very efficiently control the very unsteady flow over cavities.
These actuators have been tested for controlling large and small-scale cavity flows. These experiments, conducted over a large range of conditions, clearly demonstrated that microjets significantly reduce flow unsteadiness and dynamic loads inside and the vicinity of the cavity. This control also has a beneficial effect on the release of store from such cavities.