Control of Kelvin-Helmholtz instabilities by base-flow changes

• Grant number: 16/00944-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: April 01, 2016
• End date: September 30, 2016
• Field of knowledge: Engineering - Aerospace Engineering - Aerodynamics
• Principal Investigator: André Valdetaro Gomes Cavalieri
• Grantee: Amélie Lamarquette
• Host Institution: Divisão de Engenharia Aeronáutica (IEA). Instituto Tecnológico de Aeronáutica (ITA). Ministério da Defesa (Brasil). São José dos Campos , SP, Brazil

Abstract

Wavepackets obtained as solutions of the linearised Navier-Stokes system, using the mean field as a base flow, have been successful to model large-scale structures in turbulent jets, and are currently used as a reduced-order model to predict jet noise. Recent studies have shown that noise-reduction devices, such as chevrons and microjets, when applied to jets lead to changes in the mean flow, which in turn cause a stabilisation of wavepackets. Such devices are often developed in a trial and error basis, and there is no consensus on the best way to modify a jet to reduce its sound radiation. In this project we will use a framework based on the direct and adjoint Parabolised Stability Equations (PSE) to obtain the sensitivity of wavepackets to changes in the mean flow. Such a framework has been used in previous works by our group to study given sections of the jet using a locally-parallel assumption; here, PSE will allow a study of the full slowly-diverging velocity profile of the jet. This will allow us to set up an iterative optimisation process, where the mean flow is progressively modified so as to reduce wavepacket amplitudes, and in turn their sound radiation. Results will be useful indications on the best locations to manipulate the mean flow ofthe jet in order to obtain reductions of its associated noise.