Centrospazio/Hypersonic Aerothermodynamics

"Aerothermodynamics: The study of aerodynamic phenomena at sufficiently high gas velocities that thermodynamic properties of the gas are important." - Dictionary of Scientific and Technical Terms, McGraw-Hill 1979.

"Almost everyone has their own definition of the term hypersonic. If we were to conduct something like a public opinion poll among those presents, and asked everyone to name a Mach number above which the flow of a gas should properly be described as hypersonic there would be a majority of answers round about five or six, but it would be quite possible for someone to advocate, and defend, numbers as small as three, or as high as twelve." - P.L. Roe, 1970.

In recent years a renewed interest in hypersonic transatmospheric vehicles (both in the form of hypersonic sub-orbital transports and Single- or Two-Stage-To-Orbit space vectors) has poured new resources in aerothermodynamics and hypersonic gasdynamics studies. To address these problems a small-scale, arc-heated Mach 6/Mach 10 pulsed wind tunnel is operating at Centrospazio and is being used for fundamental research in hypersonic aerothermal flows. The tunnel is capable of producing air or helium hot flows (stagnation temperature 500-3000 K, stagnation pressure 1-35 bar) in the low to medium Reynolds number range (10⁵-10⁶ based on test section diameter), with a duration of 20-80 ms.

Hypersonic aerothermodynamic and gasdynamic activities pursued at Centrospazio are both experimental and theoretical, and include:

Papers, reports, data sets and other interesting stuff are available for download here.

The 2D compression corner configuration is representative of various aerodynamic solutions on hypersonic vehicles: i.e. deflected control surfaces, wing-body junctions, integrated engine-airframe solutions, etc. An extended experimental campaign has been performed at Centrospazio on shock-wave/boundary-layer interactions (SWBLI) in Mach 6, high temperature air flows, to assess the effect of the wall-to-stagnation temperature ratio on the flow configuration. Different stagnation temperatures (ranging from 1000 K to 2000 K), wall temperatures (ranging from 300 K to 500 K) and ramp deflection angles (10 and 15 degrees) were tested, with a Reynolds number based on the model lenght of 10⁵.

This activity is sponsored by European Space Agency, under the Future European Space Transportation Investigation Programme (FESTIP).


The 2D SWBLI test body, shown with the 15 degrees ramp.	Enlarged view of the model surface, showing the pressure taps and the thin-film heat flux gages.	Microscope close-up of a platinum thin-film heat flux gage.

A pressure-based, high-frequency (100-200 kHz) turbulence measurement technique for hypersonic flows has been recently developed at Centrospazio. By means of this technique, measurements of turbulence characteristic parameters were performed, in different Mach 7 air and Mach 10 helium flows. The most striking result so far has been the first experimental identification of a k^-11/3 inertial range in the energy spectrum of weakly compressible decaying turbulence, as recently predicted by numerical spectral simulation (EDQNM) results.

Weakly compressible turbulence energy spectrum showing the -11/3 inertial range.

More recently, we've been experimenting different wavelet-based techniques for turbulent signal processing: we've focused on continuous wavelet transforms using Morlet's, Paul's and Gaussian wavelet bases. The same streamwise turbulent velocity signal has been analyzed using different wavelets, across the same scale range: results for a typical signal (16384 samples at 500 kHz) are shown below (click for larger images).

Experimental activities in hypersonic aerothermodynamics need, as a fundamental prerequisite, the availability of advanced, high performance measurement techniques. At Centrospazio both intrusive and non-intrusive techniques are studied, ranging from optical (laser, IR, liquid crystals) to thin-film and pressure-based ones. Most of these activities are collaboratively performed with University and industrial partners from Italy and other countries: recent partners include University of Oxford (UK) and Syracuse University (USA).


A miniaturized 5-hole probe tip, for simultaneous measurements of flow speed and direction.	A multiple probe array for detailed flow mapping.	Close-up view of a dual thin-film high-frequency total temperature probe.	Close-up view of a sub-miniature high frequency pitot probe.

CENTROSPAZIO
Via A. Gherardesca, 5 - 56014 Ospedaletto, Pisa, Italy
Tel: +39 050 985097 / 985072 - Fax: +39 050 974094
E-mail: centrospazio@cpr.it


Morlet (k0=6) CWT of a typical turbulent signal.	Paul (order 4) CWT of a typical turbulent signal.	Gaussian (derivative 1) CWT of a typical turbulent signal.	Gaussian (derivative 2) CWT of a typical turbulent signal.