Design of Static Pressure Probes for Improved Free-Stream Characterization in Hypersonic Wind-Tunnels

Abstract

Slender fast-response static pressure probes are tested in the Longshot hypersonic windtunnel with free-stream Mach number larger than 10 and Reynolds number 30000 ReD 60000 based on the probe diameter. They aim at improving the characterization of the freestream. Numerical simulations predict the wall pressure measured to be within 5% of the free-stream static pressure. The viscous effects along the probes are found experimentally to be limited for L /D > 16.5 in agreement with numerical results. Limited influence of the angle of attack of the probes is found for α < 2 • thanks to the probing geometry used. The free-stream quantities at the nozzle exit (Mach, Reynolds...) are derived from the static pressure measurements and compared to those estimated assuming an isentropic nozzle flow expansion. The usefulness of static pressure probes is demonstrated through their ability to detect possible non-isentropic nozzle flow expansions which do not influence traditional measurements such as the test section stagnation pressure. This direct access to free-stream quantities allows to significantly improve the accuracy on the free-stream quantities and benefits to the characterization of hypersonic wind-tunnel flowfields.

Flow characterization and boundary layer transition studies in VKI hypersonic facilities (Invited)

“…The detailed design and calibration procedure are reported in Ref. 41. Free-stream static pressure measurements are used (in combination to the pressure and heat flux measurements at the stagnation point of an hemispherical probe with a diameter of 25.4 mm) to determine all free-stream flow properties of interest.…”

“…The procedure has been detailed in Ref. 41 and is based on the use of the Fay-Riddell equation. 42 The interest of this method with respect to the one used previously 43 is that it only requires test section measurements to characterize the hypersonic flow.…”

Hypersonic Boundary Layer Transition on a 7 Degree Half-Angle Cone at Mach 10

“…This remarkable agreement between experimental and LST results is considered as an additional proof that the method used in the Longshot wind tunnel to estimate the flow conditions (relying on the measurement of the free-stream static pressure 32 ) is accurate and well suited for hypersonic free-stream flow characterization.…”

“…The relevant technical details and the operation of this static pressure probe have been reported in Ref. 32. Good confidence has been obtained in the free-stream characterization using these types of probes.…”

“…Group velocities are compared with the free-stream flow velocity (determined from independent measurements following the method described in Ref. 32 and accurate to 2σ = ±5%) and the corresponding theoretical boundary layer edge velocity (derived from a Taylor-Maccoll flow solution). The decaying trend for u ∞ is associated to the working principle of the wind-tunnel.…”