Abstract:

ESDU 97030 describes the use of VGK, which applies only when the boundary layer is attached, to estimate a separation boundary, in terms of lift coefficient and Mach number, using the method of ESDU 81020 which essentially relies on calibrating VGK against experimental data. There the boundary is defined as corresponding to conditions on the upper surface of the aerofoil for which the shock strength and the adverse pressure gradient are sufficiently severe for the trailing-edge pressure coefficient, relative to its trend with increasing lift coefficient or Mach number in attached flow, to have decreased by 0.05. ESDU 81020 derives two criteria, either of which has to be met for a point to lie on that separation boundary. One criterion relates to conditions just ahead of an upper surface shock wave and one to conditions in the upper-surface flow near the trailing edge. The estimation of such a point requires a number of VGK runs, the first being made for conditions where there are significant margins for both criteria. Successive runs are then made at increasing angle of attack until one criterion is close to zero for two successive runs (required to ensure VGK convergence). A program is provided to manage those calculations and provide a record of the flow conditions and criteria margins. Results from example calculations for two aerofoils are given and the estimated separation data fall within the limits of accuracy suggested in ESDU 81020.

See also:

• ESDU 96028: VGK method for two-dimensional aerofoil sections. Part 1: Principles and results
• ESDU 96029: VGK method for two-dimensional aerofoil sections. Part 2: user manual
• ESDU 98031: VGK method for two-dimensional aerofoil sections. Part 4: estimation of excrescence drag at subsonic speeds
• ESDU 99032: VGK method for two-dimensional aerofoil sections. Part 5: design to a specified upper-surface pressure distribution
• ESDU 01033: VGK method for two-dimensional aerofoil sections. Part 6: aerofoil with simple hinged flaps