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Shape Optimization for Delay of Laminar-Turbulent Transition
Pralits, J. O.,
A method using gradient based optimization is introduced for design of wing profiles with the aim of Natural Laminar Flow as well as minimum wave drag.
The Euler equations of gas dynamics, the laminar boundary layer equations for compressible flows on infinite swept wings, and the linear parabolized stability equations (PSE) are solved in order
to analyze the evolution of convectively unstable disturbances.
Laminar-turbulent transition is assumed to be delayed by minimizing a measure of the disturbance kinetic energy of a chosen disturbance, which is computed using the PSE.
The shape gradients of the disturbance kinetic energy are computed based on the solutions of the adjoints of the state equations named above.
Numerical tests are carried out to optimize the RAE~2822 airfoil with the aim to simultaneously delay the transition, reduce the pressure drag coefficient and maintain the coefficients of lift an
d pitch moments. Constraints are also applied on the geometry. Results show a reduction of the total amplification of a large number of disturbances, which is assumed to represent a delay of the
transition in the boundary layer. As delay of the transition implies reduction of the viscous drag, the present method enables shape optimization to perform viscous drag reduction.