Influence of Viscous Effects on Impact Tubes

Abstract

Abstract Experiments were conducted to determine the effect of viscosity on the pressure rise recorded by a blunt-nosed impact tube in incompressible flow. The results are presented in terms of the pressure coefficient (Cp ≡ 2Δp/ρV∞2) as a function of Reynolds number (Rey ≡ V∞α/ν), where Δp is the excess of stagnation-point pressure over free-stream static pressure, V∞ is the free-stream velocity, α is the radius of the impact tube, ρ is the fluid density, and ν is the kinematic viscosity of the fluid. Above Reynolds numbers of 1000, there is no effect of viscosity, and Cp is equal to unity. Between Rey ≌ 50 and Rey ≌ 1000, Cp is slightly less than unity, but has a minimum value of 0.99. For values of Rey less than 50, Cp is always greater than unity. When the Reynolds number is below unity, the pressure rise is independent of the fluid density, and the data may be represented approximately by the formula Cp ≌ 5.6/Rey. The results are compared with the experimental investigations of Barker and of Homann, and with the theoretical studies of Stokes and of Homann.