poster - experimental duplication of venus atmospheric entry flow
DESCRIPTION
Poster presented at the VEXAG11 meeting on the 19th of November 2013.TRANSCRIPT
Experimental Duplicationof Venus Atmospheric Entry FlowGuerric de Crombrugghe, R. Morgan, T. J. McIntyre, F. [email protected]
Challenges
Venus atmospheric entry conditions are exception-ally harsh:
• High altitude:
� 11 · · · 12 km/s entry velocity,
� 15 · · · 50 g′s peak deceleration,
� 3 · · · 40 MW/m2 peak heat �ux,
� ∼ 50% radiative heating.
• Medium altitude:
� sulphuric acid cloud layer,
� up to 100 m/s high altitude winds,
� > 725 K and 9, 200 kPa at surface.
0 2 4 6 8 10 12
10−4
10−3
10−2
10−1
Flight velocity [km/s]
Fre
e−
str
ea
m d
en
sity [
kg
/m3
]
Mars direct ballistic entryPioneer Venus Day probe, 1978
Slowest Venus entryVega 1, 1984
Problem
Three generations of probes have plumbed the at-mosphere of Venus. Their heat shields were greatlyoversized as the physics of Venus atmospheric entrywere not very well understood.
Venera Venera 2/2 Pioneer Venus
1st generation 2nd generation multiprobe
(1967-1972) (1975-1984) (1978)
There is currently not enough experimental data tovalidate aerothermal models or develop new ones.
The X2 superorbital tube
The X2 superorbital tube at the University ofQueensland, Australia, is amongst the only facil-ities able to duplicate �ight conditions for Venusatmospheric entry.
It can operate either as an expansion tube (a),allowing to study the entire �ow�eld over a scaledmodel, or as a shock tube (b), to study only thephysics of a normal shock.
Shock tube results
Relevant conditions can theoretically be achievedusing X2 in shock tube mode. Similar data pointswere obtained in the Electric Arc Shock Tube(EAST) at NASA Ames [1].
6 7 8 9 10 11 12
101
102
103
Shock velocity [km/s]
Sta
tic p
ressure
[P
a]
Day probe
Without secondary driver
With secondary driver (optimum)
EAST data points
Radiative heating starts
Radiative heating stops
Peak radiative heating
Test case: Pioneer Venus
The Pioneer Venus mission presents several advan-tages to study the hypersonic segment of the tra-jectory:
• Four probes with the same geometry (onelarge, three small) but di�erent entry condi-tions → allows for a wide range of investiga-tion with a single model,
• Accurate trajectory data is available [2],
• Carried an heat shield experiment (only in-�ight experiment for Venus),
• Several numerical rebuilding of the �ight wereperformed (see for example [3]).
Expansion tube results
A test campaign was performed to design appro-priate test �ows. Conditions in the vicinity of thehigh altitude segment of the trajectory were ob-tained, where both radiative and convective heat-ing loads are signi�cant. A better match can eas-ily be obtained by reducing the equivalent velocity,thereby reducing the free-stream density (movingNorth-West on the graph below).
0 2 4 6 8 10 12 1410
−4
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Equivalent flight velocity [km/s]
Fre
e−
str
ea
m d
en
sity [
kg
/m3
]
Day probeNorth probeNight probePeak radiative heatingPeak total heatingx2s2189x2s2194x2s2195
1/10 model
Flight
Next step
Another test campaign will be performed to mea-sure the spectra along the stagnation line of a Pio-neer Venus probe model, as well as other quantitiessuch as the shock stand-o� distance. The spectragives valuable information on the species and tem-perature distribution, and the radiative heating.
Typical shock layer radiation traces, from [1].
The scaling parameter for high-enthalpy �ows is thedensity multiplied by a length scale ρL. By usingdi�erent model size in the same �ow conditions, dif-ferent points of the trajectory will be duplicated aslong as the probe's velocity is the same.
0 2 4 6 8 10 12
10−4
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Flight equivalent velocity [km/s]
Fre
e−
str
eam
density [kg/m
3]
Flight
References
[1] B. Cruden. Absolute Radiation Measurement DuringPlanetary Entry in the NASA Ames EAST facility. 27thInternational Symposium on Rare�ed Gas Dynamics,2011.
[2] A. Sei� and D.B. Kirk. Structure of the Venus Meso-sphere and Lower Thermosphere from MeasurementsDuring Entry of the Pioneer Venus Porbes. Icarus, 49:49-70, 1981.
[3] C. Park and H.-K. Ahn. Stagnation-point Heat Trans-fer Rates for Pioneer-Venus Probes. Journal of Thermo-physics and Heat Transfer, 13(1):33-41, 1999.