VKI Seminar Series 2023

VKI Seminars Series

Free registration in respect with the VKI eligibility criteria. You will receive the information to join the seminar of your choice after the registration.

Aerodynamic interactions in supersonic and hypersonic rarefied flows (online - open to public)

Dr. Vincente Cardona,  ICARE, CNRS, France

Abstract: When a spacecraft re-enters Earth's atmosphere, or in the case of a destructive space debris re-entry, the problem of proximal bodies should be considered. In particular, shock/shock  interferences (SSI) can occur and affect the structure of the spacecraft or the debris trajectory. Depending on the altitude, the objects velocity is hypersonic and they evolve in a rarefied environment, leading to predominant viscous effects. In order to better understand the impact of rarefaction level on SSI, an experimental study was conducted in the MARHy wind tunnel (ICARE, CNRS, France). SSI were obtained with the interaction of two spheres in supersonic and hypersonic low-density flows. Different relative positions were explored to identify various types of interferences occurring in these flows, characteristic of altitudes between 69 and 93 km. Results focus on the visualisation of the SSI, drag and lift forces, and wall pressures measurements. The analysis revealed an important contribution of the viscous effects on the impact of SSI and thus on the aerodynamics of the following sphere.

In the hypersonic case, for which the viscous effects are even greater due to a combination of hypervelocity and low density, the observation of SSI did not allow the identification of clear interference structures. It will be more appropriate to talk about shock/shock mixing layer with strong aerodynamic effects.

Experimental feedback control of separated and open-cavity flows with MEMS Technologies (online - open to public)

Dr. Thomas Arnoult, Institut d'électronique, de microélectronique et de nanotechnologie, IEMN

Abstract: Flow control is a multidisciplinary domain combining fluid dynamics, control theory and technology design, which aims at modifying a flow natural behaviour in order to obtain positive changes. Fluid dynamics helps understanding the physics of plants to be controlled and set the objectives to be reached, such as lift enhancement, drag or noise reduction or limiting induced structural vibrations. Control theory helps defining the most adapted control strategy to be employed in the case of reactive control. Technology design, based on fluid dynamics and control theory requirements, helps conceiving adapted actuating and sensing technologies. In this work closed-loop control of two canonical flow configurations is proposed: one targeting the control of a separated flow over a NACA 4412 plain flap and one focusing on the control of flow instabilities developing in an open-cavity flow. On the plain flap configuration, the control is implemented with conventional technologies but the focus is brought onto the implementation of two novel control laws, which successfully counter the development of the separated flow. Further measurements show the control robustness towards variations in the flow conditions. However, on such a configuration, one aims at modifying the flow mean properties without benefiting from the flow natural instabilities. The second case focuses on an open-cavity flow, on which control can benefit from the flow natural instabilities. Closed-loop control of this flow configuration is implemented with MEMS (Micro Electro Mechanical Systems) actuators and is based on the design of a controller using a structured H approach. Closed-loop control experiments damp the open-cavity flow resonance by 13 dB and highlight the controller robustness properties.

Short Biography:  Thomas Arnoult received the Engineering Degree from ISAE-ENSMA (Institut Supérieur de l’Aéronautique et de l’Espace-Ecole Nationale Supérieure de Mécanique et d’Aérotechnique) and a Degree of Master of Science in Aerospace Dynamics from the Cranfield University (United Kingdom). After graduation in December 2019, he obtained his PhD degree in Mach 2023 at the IEMN, UMR CNRS 8520 Institute, in partnership with the ONERA, the French Aerospace Lab, regarding the use of innovative micro-actuators and micro-sensors in active flow control strategies.