A Model for Prediction of STOVL Ejector Dynamics

A semi-empirical control-volume approach to ejector modeling for transient performance prediction is presented. This new approach is motivated by the need for a predictive real-time ejector sub-system simulation for STOVL integrated flight and propulsion controls design applications. Emphasis is laced on discussion of the approximate characterization of the suggests transient flow predictions are possible with a model based on steady-flow data. A practical test case is presented to illustrate model calibration. mixing process central to t g rust augmenting ejector operation. The proposed ejector model INTRODUCTION For the short take-off vertical landing (STOVL) aircraft configuration shown in Figure 1, the thrust augmenting ejectors placed at each wing root must be included in the propulsion system simulation. Integrated flight and propulsion control (IFPC) studies require ejector component ' simulations that must run accurately in "real-time". Since accuracy is typically synonymous with a high level of model detail, constructing a transient ejector model to fit the simulation requirement is not an easy task. A useful ejector characteristic to know the frequency response of ejector thrust. If the ejector response is outside the bandwidth of the flight control system then a simple quasi-steady ejector model or look-up table is all that is needed. On the other hand, if the ejector response falls within the range of the flight control (or if a new ejector design has an unknown response) a high-fidelity ejector simulation is required; this paper explores an ejector modeling approach to fill the latter requirement. There are two basic perspectives generally employed to set the mathematical framework for the ejector mass, momentum, and energy balances; the choice is easy when the intended simulation application is considered. One approach is based on first principles and typically blends the full unsteady Navier-Stokes e uation with a tubulence model. The result is cast design flavor to the analysis, the solution to the final set o equations is not amicable to real-time execution in the foreseeable future; another problem concerns identification of the appropriate turbulence model to use for description of the mixing region. P in, for example, finite-difference form. Alt 1 ough this a proach provides a desireable ejector