Flow systems play a major role in the operation and performance of modern aerospace applications.
Understanding their governing physical mechanisms is crucial for developing new technologies that optimize the efficiency and safety of future generations of aircraft. The vast majority of flow configurations encountered in applications of interest in the aerospace industry are unsteady, and exhibit aperiodic or chaotic motions (i.e., turbulent flow) whose dynamic behaviour is not well understood. Examples include large regions of separated flow induced by wings at quickly varying high angle of attack or the interaction between the separated flow region in the suction side of a low-pressure turbine blade and the impinging wake induced by adjacent blades.
Stability and sensitivity analysis offers a physics-based theoretical framework for understanding the evolution of perturbations in a given flow field and to reveal actuation mechanisms that can be exploited to achieve flow optimisation and control.
However, almost all flow stability and sensitivity studies available up to date are based on time-invariant (either steady or time-averaged) or time-periodic flows. These approaches fail to provide the necessary framework for configurations in which the underlying flow is either unsteady or a representative mean state cannot be defined, therefore preventing the access to relevant dynamic information about the behaviour of coherent structures in chaotic and aperiodic flows. Given this shortcoming, ground-breaking theoretical/numerical approaches are necessary to provide new insight into the behaviour of unsteady flow systems, and to develop models for their prediction and theoretically-founded control.
The goal of the STALSUns project is to develop a new methodology capable of obtaining the short-time stability characteristics and the sensitivity of compressible, three-dimensional unsteady flows of practical interest. The scientific objectives of the project can be summarized as:
STALSUns proposes the development and implementation of a theoretical/numerical tool that employs finite-time Lyapunov exponent analysis together with a compressible high-order CFD solver and adjoint shadowing methods, which can be used to obtain the instability characteristics of complex unsteady flows and the sensitivity of finite but long-time averaged quantities of interest. The expected project contributions beyond the state of the art are, on the hand, the development of a methodology that enables the effective application of finite-time stability analysis and sensitivity analysis to unsteady state (aperiodic or chaotic) flows of interest in industrial applications, advancing beyond the current academic applications. On the other hand, the successful characterization of coherent structures for the complex flows analysed will produce new insight about the flow dynamics which has not been directly accessible before using high-fidelity CFD simulations or experiments. This will pave the way to new modelling tools and concepts towards efficient flow control for these kinds of flows.
The research undertaken during the project is expected to have a scientific impact on the fields of dynamical systems analysis, fluid mechanics, aerospace engineering, renewable energy engineering and meteorology and climate sciences. The main expected scientific contributions are:
The physical insight provided by the proposed analyses will be used to inspire novel flow-control concepts that have the potential to be exploited in industrial design. In the long term, the maturation and implementation of such flow-control mechanisms into real designs would enable the development of key technologies that increase the efficiency, reduce the emissions, and mitigate the noise of future generations of flight vehicles.
From the socioeconomic point of view, the outcomes of this research project are expected to contribute to achieve the objectives set in Europe’s vision for aviation (Flightpath 2050), which targets highly ambitious environmental goals to lead the world in sustainable aviation products and services, namely: a 75% reduction in CO2 emissions, a 90% decrease in NOx emissions and a 65% reduction in the perceived aircraft noise. In particular, the research performed during this project is expected to have a positive impact on the EU sustainable development goal (SDG) number 13: Climate Action.
STALSUns is also expected to have a big impact on the career of the postdoctoral researcher. Through undertaking the project, the researcher will establish solid collaborations and obtain international recognition within the hydrodynamic stability and flow-control communities. This will bring the opportunity to access high-quality funding schemes and positions that enable a higher level of independence as a researcher, thus allowing him/her to approach the long-term career goal of leading a research group. On the one hand, the researcher will gain top level technical skills in the numerical modelling of complex dynamical systems and data-processing technologies, and will consolidate an expertise in three-dimensional compressible flow CFD simulations. On the other hand, thanks to the dedicated training in university teaching, he/she will be prepared to teach in graduate and undergraduate university courses in the future. This, in turn, will strengthen the possibility to access an assistant professor position at a high-level academic institution in Europe.
