Application of Computational Methods in Drag Reduction for Wing Sections using Laminar Flow Control Technique (2003)

Application of Computational Methods in Drag Reduction for Wing Sections using Laminar Flow Control Technique (2003)

Ahmad Sedaghat

sedaghat@cc.iut.ac.ir

 Department of Mechanical Engineering

Isfahan University of Technology, Isfahan 84156-83111, Iran

 University Internal Research Project no. 1MEB831 on 28/07/1383 (in Farsi)

 Abstract

In present research, the effects of surface suction on the stability of flow around several airfoil flows have been investigated. The overall purpose of this research is attaining laminar flow over the airfoil surfaces. Thus, the surface suction was applied to delay the flow transition point from laminar to turbulent and also to maximize the lift to drag ratio. For doing this, it is required to solve flowfield and to determine the transition point accurately. A CFD code in FORTRAN using an implicit Total Variation Diminishing (TVD) scheme was used to solve two-dimensional Navier-Stokes equations. For determination of transition point, the e^N method was used. This method is based on the linear stability theory uses the eigenvalues of Orr-Sommerfeld equation for determining the amplification rates of disturbance waves. In this research, a finite difference method was used for solving the Orr-Sommerfeld equation. For validation of results obtained using the e^N method, the results were compared with experimental data for the NACA0012 airfoil. In the second part of this report, flow control with surface suction around airfoil sections has been conducted. In order to validate the flow solver, the results of TVD code for flows with and without suction around the VFW-VF-2 airfoil compared with experimental data and a good agreement was observed. Next, an optimization process was performed to measure effects of parameters on surface suction such as the suction slot location and the extent of sucked flow through slots for the flow around NACA65₃-018 airfoil. This process was aimed to control transition point using the results obtained from flow stability analysis. In all the cases studied, transition delayed using suction regardless of suction positions. However, the maximum delay in transition was obtained when the location of surface suction situated between the critical point and transition point because of rapidly growing disturbances within this gap. For the aerodynamic coefficients in all suction cases, the lift coefficient was increased and the drag coefficient was decreased except for a few cases. However, in all cases studied the lift to drag ratio was increased with surface suction. Another interesting feature of surface suction is removing or reducing the flow separation size which is observed in our results.

 Key Words: hydrodynamic stability analysis, boundary layer flows, Orr-Sommerfeld equation, transition prediction, e^N method, laminar flow control, surface suction