Structural Strength of Flare-type Membrane Aeroshell Supported by Inflatable Torus against Aerodynamic Force

Transcription

1 Structural Strength of Flare-type Membrane Aeroshell Supported by Inflatable Torus against Aerodynamic Force Kazuhiko Yamada (JAXA/ISAS) Takuya Sonoda (Tokai University) Kyoichi Nakashino (Tokai University) Takashi ABE (JAXA/ISAS)

2 Contents Background Low-ballistic-coefficient atmospheric entry system Objectives Preliminary prediction Experimental setup and model 6.5m x 5.5m Low-speed wind tunnel at JAXA Chofu Results Standard model Reinforced model Conclusions 2

3 Background Recently, the space activities become various and active. Withstand Aerodynamic heating In order to support these space activities, the frequent, reliable and low-cost space transportation system between space and planet surface is necessary One of the candidates is flexible aeroshell system Avoid Aerodynamic heating Vehicle re-enters into atmosphere with low aerodynamic heating and make soft landing without a parachute Flare-type membrane aeroshell supported by inflatable torus. A reentry demonstration using a sounding rocket will be carried out in December 2011 at earliest. 3

4 Objectives We focus on flare-type membrane aeroshell supported by inflatable torus. <Merits> Whole aeroshell was made of only thin membrane. Required inflatable structure was minimized. Easy to make a larger and lighter aeroshell. Inflatable torus Thin membrane flare <Issue to resolve> The structural strength is not understood completely during the free flight. There are no data about actual developed aeroshell for the flight These data are necessary to design the real experimental vehicle. <Objectives in this study> Main body To understand structural strength of flare-type membrane aeroshell supported by inflatable torus against aerodynamic force during free flight. Especially, this study focused on the actual experimental vehicle for a reentry demonstration using a sounding rocket. 4

5 Preliminary prediction The preliminary prediction for structural strength can be derived considering the balance between compressive force by aerodynamic force and tensile force by inner pressure. F D 1 2 C AR cos in sin out 2 r p (at critical condition) Relation between the total drag force and inner pressure when the aeroshell collapsed was investigate in this study. In this assumption, aeroshell was collapsed in only local crippling mode. Crippling mode This prediction is absolutely preliminary Need the experiment to confirm it 5

6 Past research <Weight load test> Compression force acting on the inflatable torus was reproduced using a support ring and weights Structural strength strongly depend on the size of support ring. <Low-speed wind tunnel test (small model) > Aerodynamic force is used for the external force to simulate the flight condition. Support ring Nylon Weight Qualitative trend is understood. But, structural strength depends on configuration, material and fabrication method of the model. Large low-speed wind tunnel test using full scale model which have 1m-diamter aeroshell ZYLON 50cm 6

7 Experimental Model Capsule diameter : 200mm Capsule configuration : Hemisphere Flare angle : 65 deg (70 deg (Reinforced model)) Torus tube diameter : 100mm Torus outer diameter : 1200mm Same size, material and fabrication method as the actual experimental vehicle of reentry demonstration using a sounding rocket 7

8 Experimental facility and method <6.5m x 5.5m Low speed wind tunnel> Located in JAXA Chofu <Experimental system block diagram> 8 Test section : 6.5m x 5.5m Velocity : 70m/s (maximum) <Test procedure> The inner pressure of the inflatable torus can be adjusted from outside of the wind tunnel. 0) The drag force acting on the whole model was measured by the balance system before the structural strength tests ) Enough gas was injected into the inflatable torus to withstand the drag force and keep configuration in the flow. 2) The inner pressure in the inflatable torus decrease in keeping the flow velocity constant. 3) The inner pressure when the aeroshell was collapsed was recorded.

9 Structural strength Aeroshell collpased Relation between total drag force and Inflatable pressure Aeroshell is stable Critical total drag force is proportional to inflatable pressure when p > 10kPaD 9

10 Comparison with prediction Relation between total drag force and Inflatable pressure Comparison with prediction F D 1 2 C AR cos in sin out 2 r p r = 0.05m Θ in = 45 deg Θ out = 75 deg C AR = 0.97 F ( ) 3.79 ( ) D kgf p kpa prediction Experimental data did not agree prediction Stable aeroshell Collapsed aeroshell V=40m/s Pin=130kPa 10 Fold in a half Out-of-plane buckling deformation cause the reduction of the structural strength

11 Reinforcing inflatable torus Standard inflatable cylinder Layering structure Fiber direction outside Fiber direction ZYLON spun yarn textile 0.3mm Reinforced inflatable cylinder inside Silicon rubber sheet 0.3mm Add ZYLON filament layer whose fiber direction was shifted in 45 deg in order to enhance the torsional rigidity to prevent out-of-plane buckling. Fiber direction outside Fiber direction ZYLON filament textile ZYLON spun yarn textile Silicon rubber sheet inside 0.15mm 0.3mm 0.3mm 11

12 Improvement about configuration V=40m/s Reinforced model V=40m/s Standard model Reinforced inflatable torus prevent the out-of-plane buckling deformation. 12

13 Structural strength Relation between total drag force and Inflatable pressure Collapsed mode Reinforced torus? prediction Is this crippling? (cf. standard torus) 13 Reinforced inflatable aeroshell enhance the structural strength. But its result is different from a preliminary prediction which considered only crippling.

14 Conclusions Our group carried out R&D about innovative reentry system using flexible aeroshell. Structural strength of flare-type membrane aeroshell supported by inflatable torus against aerodynamic force was investigated to design the actual vehicle. Low-speed wind tunnel tests was carried out using 1.2-meter-diameter aeroshell and following results were acquired. Critical drag force that aeroshell collapsed is proportional to inflation pressure. Out-of-plane buckling deformation reduce the structural strength. Enhancement of the torsional rigidity of torus can prevent out-of-plane buckling. However, the preliminary prediction which consider crippling collapse did not agree any experimental data. We have to develop the accurate prediction about structural strength to design an actual vehicle in the future works 14

15 Acknowledgement The 6.5m x 5.5m low speed wind tunnel test was carried out with the collaboration of the Wind Tunnel Technology Center in Aerospace Research and Development Directorate, JAXA. We would like to thank to the staff of the JAXA 6.5m x 5.5m lowspeed wind tunnel for the appropriate supports and advices. 15