An experimental flow with zero skin friction throughout its region of pressure rise

Abstract

A flow has been produced having effectively zero skin friction throughout its region of pressure rise, which extended for a distance of 3 ft. No fundamental difficulty was encountered in establishing the flow and it had, moreover, a good margin of stability. The dynamic head in the zero skin friction boundary layer was found to be linear at the wall (i.e. u ∞ y½), as predicted theoretically in the previous paper (Stratford 1959).The flow appears to achieve any specified pressure rise in the shortest possible distance and with probably the least possible dissipation of energy for a given initial boundary layer. Thus an aerofoil which could utilize it immediately after transition from laminar flow would be expected to have a very low drag. A design pressure distribution (besides having the usual safety margin against stall) should have a slightly more gradual start to the pressure rise than in the present experiment, as small errors close to the discontinuity can cause difficulty.

Optimal Shape Design of a Two-Dimensional Asymmetric Diffuser in Turbulent Flow

“…It is clear from (4) and (5) that the optimality condition for maximum cost function is /0, iM unon ¶ ¶=G (6) i.e. zero skin friction on the diffuser wall, which coincides with the physical intuition of Stratford [1,2].…”

“…In his pioneering work, Stratford [1,2] theoretically obtained a pressure distribution that maintains zero skin friction throughout the region of pressure rise inside a diffuser, and experimentally constructed a diffuser having the theoretical pressure distribution by controlling each segment of the diffuser wall. Maintaining zero skin friction along the diffuser wall suggests that the diffuser should be widened as much as possible but preventing flow separation.…”

Aerodynamic optimization of a biplane configuration using differential evolution

“…This work was directed to the development of high lift airfoils and can be thought of as an inverse design problem, as we would seek to find the shape that best matched a prescribed pressure distribution. The prescribed pressure distribution was crafted to provide a Stratford [3] pressure distribution in the adverse pressure zone and hence avoid separation. The analytical methods were based on potential flow methods that did not explicitly consider viscous effects.…”

Longitudinal Vortices in Turbulent Boundary Layers Subjected to Wall Curvature and Strong Adverse Pressure Gradients: Numerical Investigations Using LES and DNS

“…In 1959, Stratford showed how maximum flow deceleration and pressure recovery can be obtained in the shortest possible distance [9,10]. For many technical applications, this type of flow may be desirable.…”