Modeling and control of unsteady aerodynamic forces in over-expanded nozzles – MOCODYN

The control of unsteady aerodynamic forces is crucial for the aeronautical and defense industries as it would allow to improve the performance, safety and reliability of aerodynamic systems. This can be done, from the design stage, by optimizing the system, which will improve the reliability for critical missions as well as the general performance of the aircraft. Indeed, a fine reduced modeling of the unsteady pressure forces proves to be invaluable in the design phase to help to define the load cases, when designing the structures in fatigue in particular. This project is therefore part of the ongoing efforts to better understand, predict and therefore reduce undesirable aerodynamic forces, by active control or optimal design.

In the specific case of launchers or missiles nozzles, it is at start-up and during non-adapted operation that these load cases are the most problematic. The internal dislocations can generate undesirable unsteady forces orthogonal to the thrust which are harmful for the structural integrity of the engine but also possibly for the success of the mission. It should be noted, however, that if the chosen application is that of the nozzle because of the adequacy of the problem with the know-how of the team and the experimental facilities, the scope of the project is much broader because the methodology developed is not limited to these flows.

Thus, the proposed project aims at a fine reduced modeling of unsteady pressure forces based on a resolvent analysis of the flow dynamics. Indeed, this formalism allows theoretically to obtain directly the Fourier spectrum of the wall forces starting from a simple mean field of the flow. The model thus obtained is sufficiently inexpensive to be integrated into an innovative optimization loop. We therefore propose to exploit this model to obtain an optimized nozzle shape, under a double constraint of thrust maximization and unsteady forces minimization. Moreover, we propose to use the results of the solver analysis to design a fluidic control strategy for these undesirable forces. Indeed, this analysis will inform us on the optimal way to act on the flow but also on the optimal location of the actuator in the flow. We will exploit this information for the design of dedicated plasma actuators and their integration on a nozzle model. We will test in the laboratory the optimized model and its controlled counterpart.

This project is fully integrated in the thematic axis 4 (Fluids, Structures) and sub-theme 1 (fluid flows) of the ANR-ASTRID 2023 call for projects. Among the priorities of this theme, it participates in those on the control of complex fluids and aims more specifically at improving "Aerodynamic performance and optimization methods for the design of new architectures" as well as the theme of "Flow control: theoretical approaches and simulation of control, development of actuator technologies".