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Optimum Shape Design for Unsteady Flows using
The methods and resources now present in Computational Fluid Dynamics (CFD) offer the means to acquire accurate solutions of complex flow fields. In the past decade aerodynamic shape optimization (ASO) has been the focus of attention due largely to advanced algorithms that have allowed designers to calculate gradients cheaply and efficiently. The majority of work in ASO has been focused on the design of aerospace vehicles which operate in a steady flow environment. There are numerous important engineering applications in which the flow is inherently unsteady but periodic. Helicopter rotors in forward flight, turbomachinery blades and cooling fans operate in unsteady flow and are constantly subjected to unsteady loads. Optimization techniques for unsteady flows are clearly needed to improve their performance, and to alleviate the unsteady effects that 38%contribute to flutter, buffeting, poor gust and acoustic response, and dynamic stall. As yet there have been few efforts in this direction. This work focuses on the development of ASO using the time accurate and the non-linear frequency domain discrete adjoint approach. Control theory is directly applied to the time-dependent discrete flow field equations to produce the discrete adjoint equations. The first phase uses the discrete adjoint approach to develop a set of equations for the optimal control of unsteady flows. An application of the unsteady discrete adjoint equations optimizes the shape of airfoils to reduce the time-averaged drag coefficients while maintaining the time-averaged lift coefficient. The future of this research will be the successful application of this method to the design of helicopter and turbomachinery blades that are constantly subjected to unsteady forces. Results are presented for two-dimensional viscous inverse and drag minimization design using the discrete adjoint method. A detailed comparison of the approach to the traditional continuous approach is also presented. Successful application of the unsteady discrete adjoint equations to the reduction of the time-averaged drag minimization of the RAE 2822 and the VR-7 advanced rotor airfoil is also shown.
Date: 2004-04-23 à 05:30
Endroit: Local 2546, pavillon Adrien-Pouliot