Limits of Simulating Gas Giant Entry at True Gas Composition and True Flight Velocities in an Expansion Tube

Transcription

1 Limits of Simulating Gas Giant Entry at True Gas Composition and True Flight Velocities in an Expansion Tube 8th European Symposium on Aerothermodynamics for Space Vehicles C.M. James, D.E. Gildfind, R.G. Morgan, S.W. Lewis, E.J. Fahy, T.J. McIntyre The Centre for Hypersonics, The School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD, 4072, Australia Le Laboratoire EM2C, Ecole Centrale Paris, Chatenay-Malabry, France 3rd March 2015

2 Let s start here... Figure: Artists rendition of the Galileo Probe s entry into Jupiter [1].

3 The Galileo Probe The Galileo probe s entry into Jupiter is the only entry into a gas giant that humankind has ever attempted. The probe entered the atmosphere of Jupiter on the 7th of December 1995 at a relative velocity of 47.5 km/s, and took less than 100 seconds to decelerate to 1 km/s [2]. The majority of the gas giant entry research completed in the past has been related to the Galileo probe. This includes pre-launch research completed to design the probe [3, 4, 5], and some successful post-entry CFD studies aiming to understand the issues with it [6, 7]. Where to from here though? Is the topic still relevant?

4 A new context... The US National Research Council Vision and Voyages for Planetary Science in the Decade report identified probes to Uranus [8] and Saturn [9, 10], as high priorities for future space missions, because of the important questions about the universe that gas giant entry probes can help answer. The proposed probe entry velocities are 22.3 km/s for Uranus [8] and 26.9 km/s for Saturn [9, 10] This gives us a new context to study gas giant entry. How can we better simulate gas giant entry in the future? How does ground testing fit into this?

5 Ground testing for Gas Giant Entry Due to the extreme cost of performing real flight tests, ground tests have been essential to the design of planetary entry vehicles... but they have their limitations. It is impossible, in practice, to run continuous operation planetary entry wind tunnel experiments on a test model, and decisions must be made about what to simulate. Most test facilities used to simulate planetary entry are either low velocity and long duration or high velocity, impulse facilities.

6 Ground testing for Gas Giant Entry This work focuses on the latter situation, where velocity is high but test times are short, and it focuses on understanding the limits of what can be done at true flight velocity in an expansion tube. It aims to establish the limits of what gas giant entry experiments can be performed at true gas composition and true flight velocity in the X2 expansion tube at the University of Queensland, as it can currently be configured.

7 That was a long intro... but this talk will cover: What an expansion tube is, and why it is well suited to study planetary entry. How we have simulated the X2 expansion tube for this work. The details of the condition design analysis that has been performed. Details of other experimental avenues to be explored. Conclusions.

8 The Expansion Tube Concept The expansion tube is a modified shock tunnel that incorporates an additional low pressure shock tube (called an acceleration tube ) to unsteadily expand the test gas to superorbital planetary entry conditions. Used principally for studying planetary entry phenomena from 6 12 km/s. The X2 expansion tube has been used to simulate radiating planetary entry flows for several planetary bodies in the solar system, including Earth, Mars, Titan, and Venus [11, 12]. Very short test times (X2 test times are usually µs.)

9 The X2 Expansion Tube Figure: the X2 expansion tube. Photo by David Gildfind (the only time the lab was ever clean).

10 The X2 Expansion Tube 3s Figure: Schematic and x-t diagram of the X2 expansion tube with the shock heated secondary driver tube in use. (Adapted from the work of Gildfind [13].)

11 Simulating The X2 Expansion Tube Fully characterising an expansion tube test flow is a costly computational process, requiring complex compressible, high temperature, transient, two-dimensional, axisymmetric CFD. UQ has a one-dimensional CFD code, L1d3 [14], that can simulate the facility in around an hour. This is still not fast enough to be a parametric design tool. So we wrote an equilibrium expansion tube simulator.

12 Introduction to PITOT PITOT is an equilibrium gas based expansion tube analysis code built for preliminary design and approximate characterisation of new expansion tube test conditions. Each simulation takes a minute or so, and it can be scripted to easily run parametric studies. It includes equilibrium gas effects which are important for simulating high speed conditions with a useful amount of accuracy. For this work it has been used to perform parametric studies of the performance of the X2 expansion tube.

13 Condition Design Introduction The goal of the condition design is to identify the trends that maximise the facility s performance. All conditions use a simulated Uranus entry test gas composition of 85%H 2 /15%He (by volume) based on values from the work of Conrath et al [15]. Separate Saturn entry composition analysis is not presented here, but the results were found to be very similar. Due to practical operating limits of the facility, a 0.5 Pa acceleration tube fill pressure was used for all calculations performed. Two different primary driver conditions are analysed, and the analysis of conditions both with and without a shock heated secondary driver tube is presented.

14 Measuring Performance Stagnation enthalpy (H t ) is used to compare the performance of all test conditions in this work. It is a measure of energy contained in a gas due to both its gas state and its velocity. H t = h+ U2 2 (1)

15 Conditions Without a Secondary Driver For a set acceleration tube fill pressure (p 5 ) a condition without a secondary driver will have one shock tube fill pressure that maximises performance. This was found to occur at around 2 kpa for both driver conditions analysed, so a 2 kpa shock tube fill pressure was selected.

16 Conditions With a Secondary Driver Introducing a secondary driver tube adds one more facility variable to the calculation, and things get a bit more complicated...

17 Conditions With a Secondary Driver Stagnation enthalpy (Ht, MJ/kg) a) X2-LWP-2.0 mm-0 Conditions p1 = 0.25 kpa p1 = 0.5 kpa p1 = 0.75 kpa p1 = 1 kpa p1 = 1.25 kpa p1 = 1.5 kpa p1 = 1.75 kpa p1 = 2 kpa p1 = 2.5 kpa p1 = 3 kpa p1 = 4 kpa p1 = 5 kpa Secondary driver fill pressure (p sd1, kpa) Stagnation enthalpy (Ht, MJ/kg) b) X2-LWP-2.5 mm-0 Conditions p1 = 0.25 kpa p1 = 0.5 kpa p1 = 0.75 kpa p1 = 1 kpa p1 = 1.25 kpa p1 = 1.5 kpa p1 = 1.75 kpa p1 = 2 kpa p1 = 2.5 kpa p1 = 3 kpa p1 = 4 kpa p1 = 5 kpa Secondary driver fill pressure (p sd1, kpa) Figure: How secondary driver fill pressure (p sd1 ) affects performance for different shock tube fill pressures (p 1 ). Each condition uses the same driver condition and a set acceleration tube fill pressure (p 5 ) of 0.5 Pa.

18 Conditions With a Secondary Driver 2 kpa acceleration tube fill pressure was chosen for both driver conditions as a compromise between performance and creating a usable test flow. Leaks become more of an issue with very low fill pressures, and there s the risk of not having enough test gas to produce a usable test flow.

19 Chosen Conditions It was decided to use a 2 kpa shock tube fill pressure, and a 0.5 Pa acceleration tube fill pressure for all conditions. A secondary driver fill pressure of 21 kpa was chosen for one condition, and 25 kpa for the other. Without a secondary driver, this gives a maximum stagnation enthalpy of 173 MJ/kg, producing a flight equivalent velocity of 18.6 km/s. With a secondary driver, this gives a maximum stagnation enthalpy of 270 MJ/kg, producing a flight equivalent velocity of 23.2 km/s.

20 Other Avenues to Explore Due to the fact that the previous analysis shows that the X2 expansion tube cannot currently simulate the 26.9 km/s entry velocity required to simulate Saturn entry, it is important that other avenues be explored to potentially allow the simulation of these conditions in the facility in the future. This section examines how utilising a higher amount of helium diluent than the actual entries allows hotter shock layers to be simulated at achievable shock speeds.

21 Higher Amounts of He In 1998, Stalker and Edwards [16] proposed a test gas substitution for the study of gas giant entry conditions in ground testing facilities. They showed that for inviscid gas giant entry flows the helium acted as an inert diluent and collision partner for the hydrogen molecules and atoms in the flow-field. They found that the amount of inert diluent in the flow-field did not affect the ionising relaxation of the test flow. The following figures examine how an increasing amount of helium diluent affects a simple expansion tube condition.

22 Higher Amounts of He ) ) *!++ & $,-. ($ ( & $ % & '!"# $ % & '!"# Figure: How a differing percentage of helium diluent (by volume) affects the test conditions.

23 Higher Amounts of He -. %/ '0 (0 0 (0 0 ( !"!"!"!"+!,!"+!"##!"# ' ( ) *!"#$%& ' ( ) *!"#$%& Figure: How a differing percentage of helium diluent (by volume) affects the gas properties of the gas along the stagnation line over the test model.

24 Higher Amounts of He Overall, the figures show the full extent of what is possible with higher amounts of helium diluent. They show how by increasing the amount of helium diluent in the flowfield, an approximately 19km/s flight equivalent velocity flow condition can be used to simulate the shock layers for proposed entries into Uranus and Saturn, and potentially even faster entries.

25 Conclusions It has been shown theoretically that with the use of a secondary driver section the X2 expansion tube could be used to simulate a 22.3 km/s proposed entry into Uranus using the true gas composition. It has also been shown theoretically that with increasing amounts of helium diluent in the test flow that the proposed Uranus entry and a proposed Saturn entry at 26.9 km/s could both be simulated in the X2 expansion tube without a secondary driver section.

26 Thank you for listening. Any Questions? Thank you! Any questions? Figure: Artists rendition of the Galileo Probe s entry into Jupiter [1].

27 References I [1] NASA, Solar System Exploration: Spacecraft Images, April 2013, Accessed June 3, [2] Gnoffo, P., Planetary-Entry Gas Dynamics, Annual Review of Fluid Mechanics, Vol. 31, 1999, pp [3] Lundell, J., Spallation of the Galileo probe Heat Shield, AIAA Paper , June [4] Park, C. and Balakrishnan, A., Ablation of Galileo Probe Heat-Shield Models in a Ballistic Range, AIAA Journal, Vol. 23, 1985, pp [5] Park, C., Lundell, J., Green, M., Winovich, W., and Covington, M., Ablation of Carbonaceous Materials in a Hydrogen-Helium Arcjet Flow, AIAA Journal, Vol. 22, 1984, pp

28 References II [6] Matsuyama, S., Ohnishi, N., Sasoh, A., and Sawada, K., Numerical Simulation of Galileo Probe Entry Flowfield with Radiation and Ablation, Journal of Thermophysics and Heat Transfer, Vol. 19, 2005, pp [7] Park, C., Stagnation-Region Heating Environment of the Galileo Probe, Journal of Thermophysics and Heat Transfer, Vol. 23, 2009, pp [8] Hubbard, W., Ice Giants Decadal Study, Vision and Voyages for Planetary Science in the Decade , National Academy Press, Washington, D.C., 2010, pp [9] Spilker, T. R., Saturn Atmospheric Entry Probe Trade Study, Vision and Voyages for Planetary Science in the Decade , National Academy Press, Washington, D.C., 2010, pp

29 References III [10] Spilker, T. R., Saturn Atmospheric Entry Probe Mission Study, Vision and Voyages for Planetary Science in the Decade , National Academy Press, Washington, D.C., 2010, pp [11] Sheikh, U., Morgan, R., Zander, F., Eichmann, T., and McIntyre, T., Vacuum Ultraviolet Emission Spectroscopy System for Superorbital Reentries, 18th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, Tours, France, [12] Eichmann, T., Radiation Measurements in a Simulated Mars Atmosphere, Ph.D. thesis, the University of Queensland, St. Lucia, Australia, [13] Gildfind, D., Development of High Total Pressure Scramjet Flows Conditions Using the X2 Expansion Tube, Ph.D. thesis, the University of Queensland, St. Lucia, Australia, 2012.

30 References IV [14] Jacobs, P., L1d: A computer program for the simulation of transient-flow facilities. Report 1/99, Department of Mechanical Engineering, University of Queensland, Australia, [15] Conrath, B., Gautier, D., Hanel, R., Lindal, G., and Marten, A., The Helium Abundance of Uranus from Voyager Measurements, Journal of Geophysical Research, Vol. 92, 1987, pp. 15,003 15,010. [16] Stalker, R. and Edwards, B., Hypersonic Blunt-body Flows in Hydrogen-Neon Mixtures, Journal of Spacecraft and Rockets, Vol. 35, 1998, pp