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Stability and Sensitivity Methods for Industrial Design

Periodic Reporting for period 2 - SSeMID (Stability and Sensitivity Methods for Industrial Design)

Reporting period: 2018-01-01 to 2019-12-31

Aviation contributes to more than 2% of global greenhouse gas (GHG) emissions and its activity is increasing exponentially. In the absence of further measures, carbon dioxide (CO2) emissions from international aviation are estimated to almost quadruple by 2050 compared to 2010. It is obvious that an increasing environmental concern is everyday more present in the aeronautical community, industry and research centres, having a definite influence on the way the design of the aircraft of the future.
Most of the environmental goals have a direct connection with the aerodynamic performance of the aircraft. Current aircraft are much more efficient than their original designs; and although the wing-body-tail configuration is still the standard shape for most subsonic commercial aircraft currently active, aerodynamic parameters have drastically improved. As an example, the lift to drag ratio has increased from 6 to 20, and noise emissions at take-off have been reduced as much as 40dB. Those numbers give an idea of the evolution towards more efficient designs that have been possible as a result of the combination of new methods and tools and a better understanding of the physics involved in flight. But still, the main limitation of current designs is related to unsteadiness; at the limits of the flight envelope, several not yet well understood phenomena occur; high angle of attack and maximum lift, buffet, flutter, transonic effects, turbulence, detached and highly distorted flows, or shock boundary layer interactions. Those phenomena limit the efficiency and security of current aerodynamic performance.
Activities considered in SSEMID has allowed to advance in the development of new methods and tools able to understand those complex configurations where unsteadiness and nonlinear effects are dominant; making possible to uncover the underlying physics and to provide means to control them. Additionally, SSEMID has provide doctoral training to 16 new fellows involve in high level research on several scientific fields such as high accuracy simulation, flow stability, sensitivity and flow control techniques, and to apply their research to realistic problems that currently the industrial partners are not able to solve.
In order to achieve the defined objectives, the backbone of SSEMID is structured in four technical WorkPackages:

WP1.Development of numerical tools.
WP2.Formulation of Direct and Adjoint methods.
WP3.Analysis of flow sensitivity under external perturbation.
WP4.Industrial applications of stability and sensitivity analysis

Activities in WP1 have been developed by ESR1, ESR4, ESR7, ESR11, ESR16 and ESR17 and have been focused on improving the computational efficiency of the Discontinuous Galerkin Spectral Element solvers of UPM, ICL, ONERA and UPM. In particular the development of different p-adaptation strategies, mesh generation. Implicit time-stepping methods for the Compressible Navier-Stokes equations, in particular the Explicit Singly Diagonal Implicit Runge-Kutta (ESDIRK). Finally, the application to these solvers to pulsating turbulent flows, highly detached configurations or aeroacoustic analysis of turbulent jets.

Activities in WP2 have been developed by ESR2, ESR9, ESR10, ESR15 and ESR16 and includes the development of a complete suite of tools to compute the stability of any 3D aerodynamic problem, stability and adjoint of dominant eigenmodes and sensitivity to any perturbation. Analysis of the laminar-turbulent transition of three-dimensional boundary layers, such as finite swept wings by using linear nonlocal instability theory based on parabolized stability equations (PSE). Study the influence of the presence of isolated roughness elements in the study of natural boundary-layer transition at hypersonic speeds and the existence of optimal disturbances that can lead to bypass transition by means of transient energy growth when a roughness element is present, or the analysis of the acoustic receptivity of a super-elliptic leading edge in the incompressible regime by using a global modes analysis.

Activities in WP3 have been developed by ESR3, ESR5, ESR6, ESR8, ESR14 and have been focused on the development of sensitivity and optimization tools to account for modifications of the base flow, external forcing or surface deformation. Application of data-assimilation techniques to complex flows to recover time-averaged mean-flow fields when we have extremely sparse measurements in space. Development of algorithms for the shape optimization of a piezo-electric actuator in an inkjet print head in order to minimize reverberations after a droplet has been ejected and the investigation of aeroacoustic feedback phenomena and their influence on far field noise radiation by means of experimental and numerical analysis.

Activities in WP4 are participated by all fellows but especially by ESR12, ESR13 and ESR16 and have been focused on the development of a fast yet accurate receptivity tools that are flexible enough to simulate different receptivity mechanisms in complex geometries over a wide range of flow conditions in three dimensions. Of particular interest to the present research is the influence of acoustic forcing on boundary layer receptivity. The analysis and quantification of the impact on laminar-turbulent transition of three-dimensional (3D) surface irregularities located on the leading edge of commercial aircraft wings, and the behaviour of separated flows, focused on the characterization of the inception, reattachment and separation length, that allows to develop more efficient methods to enhance or abate flow separation under non-temporally uniform inlet conditions.
SSEMID´s research focused on the stability analysis as a key element in the understanding of the current limitations of aircraft designs, and on new numerical methodologies and models applied so the aircraft manufacturing industry obtain innovative solutions. SSeMID has matured and industrialized new methods to obtain sensitivity maps of critical aerodynamic features with high impact on aircraft performance and environment, such as noise or fuel consumption. The direct applications of this methodology are flow control and advance optimization.
The research results are having a profound impact on the design of the modern aircraft. The development costs will be reduced as high performing aircraft design simulation tools will contribute to the transition of existing aircraft testing methods – mainly based on wind tunnel testing – into more automated process, relying on real time fast simulations. The product is delivered to the market in shorter a time and has a much more mature design improving its safety and stability.
The 16 young researchers employed by the project have obtained their doctoral degrees within an international and intersectoral environment. They have taken an active part in the innovation process by developing new methodologies and incorporating immature technologies into the industrial design processes. In this way, they were introduced to a global view of the design process: from understanding the mathematical basis of numerical methods for simulation in engineering to their industrial application.
Transition to turbulence
SSEMID_GROUP_lecture_series
Flow control of trailing edge flow
Flow simulation of complete aircraft