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Experimental Duplication of Venus Atmospheric Entry Flow Guerric de Crombrugghe, R. Morgan, T. J. McIntyre, F. Zander g.decrombrugghe@uq.edu.au

Challenges

Venus atmospheric entry conditions are exceptionally harsh: • High altitude:

 11 ¡ ¡ ¡ 12 km/s entry velocity,  15 ¡ ¡ ¡ 50 g 0 s peak deceleration,  3 ¡ ¡ ¡ 40 M W/m2 peak heat ux,  âˆź 50% radiative heating. • Medium altitude:  sulphuric acid cloud layer,  up to 100 m/s high altitude winds,  > 725 K and 9, 200 kP a at surface.

The X2 superorbital tube at the University of Queensland, Australia, is amongst the only facilities able to duplicate ight conditions for Venus atmospheric entry.

Test case: Pioneer Venus

The Pioneer Venus mission presents several advantages to study the hypersonic segment of the trajectory: • Four probes with the same geometry (one

large, three small) but dierent entry conditions → allows for a wide range of investigation with a single model, • Accurate trajectory data is available [2], • Carried an heat shield experiment (only inight experiment for Venus), • Several numerical rebuilding of the ight were performed (see for example [3]).

Mars direct ballistic entry Pioneer Venus Day probe, 1978 −2

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Another test campaign will be performed to measure the spectra along the stagnation line of a Pioneer Venus probe model, as well as other quantities such as the shock stand-o distance. The spectra gives valuable information on the species and temperature distribution, and the radiative heating.

Typical shock layer radiation traces, from [1].

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The scaling parameter for high-enthalpy ows is the density multiplied by a length scale Ď L. By using dierent model size in the same ow conditions, different points of the trajectory will be duplicated as long as the probe's velocity is the same.

Slowest Venus entry Vega 1, 1984

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6 8 Flight velocity [km/s]

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Expansion tube results

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Problem

Three generations of probes have plumbed the atmosphere of Venus. Their heat shields were greatly oversized as the physics of Venus atmospheric entry were not very well understood.

Shock tube results

Relevant conditions can theoretically be achieved using X2 in shock tube mode. Similar data points were obtained in the Electric Arc Shock Tube (EAST) at NASA Ames [1].

A test campaign was performed to design appropriate test ows. Conditions in the vicinity of the high altitude segment of the trajectory were obtained, where both radiative and convective heating loads are signicant. A better match can easily be obtained by reducing the equivalent velocity, thereby reducing the free-stream density (moving North-West on the graph below).

Pioneer Venus multiprobe (1978)

There is currently not enough experimental data to validate aerothermal models or develop new ones.

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Day probe Without secondary driver With secondary driver (optimum) EAST data points Radiative heating starts Radiative heating stops Peak radiative heating 8

9 10 Shock velocity [km/s]

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4 6 8 Flight equivalent velocity [km/s]

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Flight

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Day probe North probe Night probe Peak radiative heating Peak total heating x2s2189 x2s2194 x2s2195

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References

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1/10 model

Free−stream density [kg/m3]

Venera 2/2 2nd generation (1975-1984)

Static pressure [Pa]

Venera 1st generation (1967-1972)

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Flight

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Free−stream density [kg/m3]

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Next step

It can operate either as an expansion tube (a), allowing to study the entire oweld over a scaled model, or as a shock tube (b), to study only the physics of a normal shock.

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Free−stream density [kg/m3]

The X2 superorbital tube

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6 8 10 Equivalent flight velocity [km/s]

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[1] B. Cruden. Absolute Radiation Measurement During Planetary Entry in the NASA Ames EAST facility. 27th International Symposium on Rareed Gas Dynamics, 2011. [2] A. Sei and D.B. Kirk. Structure of the Venus Mesosphere and Lower Thermosphere from Measurements During Entry of the Pioneer Venus Porbes. Icarus, 49:4970, 1981. [3] C. Park and H.-K. Ahn. Stagnation-point Heat Transfer Rates for Pioneer-Venus Probes. Journal of Thermophysics and Heat Transfer, 13(1):33-41, 1999.

POSTER - Experimental Duplication of Venus Atmospheric Entry Flow  

Poster presented at the VEXAG11 meeting on the 19th of November 2013.

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