Recent advancements in shape optimization of aero spiked high speed re-entry vehicle using CFD

Due to increasing demand of High Speed Re-entry vehicles for Space activities within the world, a serious issue associated with the method of deceleration down a vehicle is by the intense heat generated because of development of stronger shocks at the nose. The price of thermal protection systems (TPS) to cut back the warmth generated by the return vehicles is extremely high. In this paper, the ultimate outcome is to cut back the aero heating which is achieved by introducing a spike at frontal region of the nose. Additionally, this spike avoids the deterioration and preserves the structural integrity of space vehicle over elevated temperatures. Further, four totally different geometries of tip specifically Blunt, Slender, Snap and Pan for the aerospike has been introduced and their impact on performance is evaluated and compared with the vehicle having TPS. Hence, usage of aerospike in return vehicles is the most successful and economical over different protection system.


INTRODUCTION
Re-entry Vehicle moves at terribly high speed in suborbital, that the wave generated is extremely robust and therefore the temperature behind that shock are greatly high.And this whole heat is transmitted to the vehicle body.It is required to scale back that heat from the body, and to dissipate the warmth in to air.These hot gases then flow subsequently within the boundary of the re-entry vehicle.Therefore, our major objective of reentry vehicle design is to act as protection of the vehicle to avoid from the severe mechanics of heating.The objective of re-entry vehicle design is to reduce the warmth which fits into the vehicle and maximize that heat, that get into the air outside the vehicle.Thus, properly designed re-entry vehicle can act as protective covering and reduces the mechanics of air drag.Concerning the role of wind tunnels in fluid propulsive studies, in 1946 von Neumann aforesaid "Indeed, to a great extent, experimentation in fluid dynamics is performed under conditions wherever the underlying physical principles don't seem to be unsure, wherever the quantities to be ascertained are fully determined by known equations.Therefore, wind tunnels, for instance, are used at present, a minimum, as computing devices to integrate the PDE's of fluid dynamics."F.F.J. Schrijer, F. Scarano & B.W. van Oudheusden [1] conducted an experiment on Reattachment and Separation of Boundary layer on a Blunt shaped Cone-Flare through QIRT.Transient HT measurements are administrated on the cone flare model during a short period hypersonic facility at Mach 9 through Quantitative Infrared Thermography (QIRT).Infrared vision camera was used to compute the temperature of surface and the temperature statistics were effectively related to heat transfer co-efficient specifically by two different reduction techniques.Z. Jiang, Y. Liu & G. Han [2] conducted experiment to attain effective wave for reducing the drag underneath non-zero attack angles and additionally to avoid from severe aero heating, a new concept of the Non-ablative TPS for high speed reentry vehicles was planned and lateral jets are developed at the spike region as a renovating system of shock at front facet of hypersonic vehicles.The spike works as alternative of the bow shock at nose of a blunt vehicle, the lateral jet works to scale back the heat generated at the front of spike and diverts the shock away from the vehicle in conical shape.For the conceptual design and CFD validation the experimental visualization of flow & pressure measurements was conducted in a hypersonic wind tunnel.D. Dirkx & E. Mooij [3] investigated the abstract design of a high-speed re-entry vehicle whose effect on performance is calculated by variation of shape and geometry.The two distinct categories of form optimisation in vehicles..i.e.Capsule and winged vehicle.By victimization the local-inclination strategies and flight mechanics characteristics of these vehicles were analyzed.Entry flight regimes at Mach 3 were computed by assumptive boundary conditions.It has conjointly been studied that depending on the geometry of the structure there's important drop on pressure and temperature of body move in compressed medium however at stagnant purpose, at that the structure is modified between slendered nacile and once more compared to a blunt nacile based on the work of P. Harish et al [4].It has been studied that there's a crucial role of temperature in supersonic and hypersonic flight period due to compressible effects and the thermal load reduction strategies like counter flow ejection of fluid ` jet of lower temperature collectively of the preventive estimation based on the work of Y.Y.Zeng et al [5].It was additionally studied that there's sudden amendment of properties in fluid at the nacile portion of the re-entry vehicle because of operational speed and a spread of shocks like bow shock at nose of the vehicle.This case is analyzed by comparing with spike and without spike by observing decreasing pressure data in these highspeed vehicle based on work of C. Nataraj et al [6].Flow analysis is performed using ANSYS FLUENT 17.2.

Modelling by using Solid Works Software
The profile of the winged hypersonic re-entry vehicle is modelled through Solid works 2016 tool.The dimensions taken for the high speed moving body is as shown in the fig2.1.1.

Meshing by using Ansys Fluent 17.2
Before going to the flow analysis over the Vehicle the Vehicle model was imported from Solid works 2016 to ANSYS FLUENT 17.2.Before starting of the mesh the boundary layer is to be created around the Vehicle body.And then mesh the faces of the body by using ANSYS FLUENT 17.2.To create mesh of the domain all triangles method is inserted to map elements.Then quality of the generated mesh is checked.(figure2&3)  The temperature at the nose for the re-entry hypersonic vehicle was 908 k.(figure 5)

VALIDATION AND VERIFICATION
The experiment was done at Delft University of Technology, Netherlands.The wind tunnel was operated at a free stream Mach no.9.1.The total pressure P0 maintained in wind tunnel is ranging between 25 and 75 bars.A temperature controlled electrical heating system is used to heat the fluid (dry air) to a temperature of 873 K. (figure 7) The figure 6 shows the experimental scleren graph.This graph shows the shock wave pattern and the fluent generated shock wave pattern for the same experimental input so we are comparing the both graphs for validation.

Calculation of Heat Transfer Co-efficient (CH):
The Heat Transfer Rate is given by the relation Where the values of ρ (density), c (specific heat) and l (thickness) of the skin are

TOPOLOGY OPTIMIZATION
From the without spike results, it is observed that at nose region the temperature is very high, so that the simulation is concentrated on reducing the Temperature at nose.Thus, spike is introduced for the same model and for same input and successfully found reduction in nose temperature compared to without spike one.The following figures shows the mesh model four different designs of tip of the spike.By changing the form and geometry of spikes its effect on presentation is evaluated, during this study, the form optimisation of two categories of spikes has been studied: A spike with tip as slender & blunt (figure 9 & 10).On one facet, slender spike style reduces the drag however a lot of heating.On the opposite facet, blunt spike style produces a lot of drag.However they're choosable as aero heating reduces.To avoid intense shocks thereby minimizing the temperature, spikes are built at the nose region.
Modeling, Meshing & Fluent analysis is performed in same way as that of without spike model for the same boundary conditions.A spike of four designs was modelled at the frontal region of the high speed vehicle.Blunt spike with 40mm length and having blunt radius at tip of 3mm.slender spike of length 40 mm and having slender angle at tip of 17.06 0 .The spike length is same for Snap spike (figure 11) with radius equal to 4mm.Similarly,Pan spike (Figure 12) is having a slender angle of 17.06 0 with slant length 4.47mm.

Blunt Spiked Vehicle
For Blunt, spiked body the following pressure profile and Temperature profile is analyzed (figure 13 & 14).The temperature observed for the high speed Blunt spike vehicle was 812 K (figure 15).Due to the spike the generated shock wave scatters away and gradually lowers temperature along structure of vehicle.

Pan Spiked Vehicle
The temperature computed for the snap spiked vehicle was 820K (figure 24).It can be clearly observed in the figure 22   The figure 25 shows temperatures of without spike and with spiked vehicle that includes Blunt, Slender, Snap, and Pan Spike respectively with respect to their corresponding positions.Clearly, the nose region of without spiked vehicle is at a higher temperature than that of its other parts.However, there isn't much reduction of temperature throughout the body .In addition, spiked vehicles has showed a better response in the reduction of temperature especially at the nose.Moreover, blunt spike vehicle is much more effective followed by Snap spike then by Pan Spike.The slender one was least effective which shows similar trend as of without spike vehicle and was below it.

CONCLUSION
Keeping in view of future requirements for Hypersonic field of research as well as to generate data base towards extending some of existing static temperature, correlations, a detailed CFD study of hypersonic laminar surface flows on several spiked models will have relevance to reentry missions.
In this paper, design and optimization for the reentry vehicle in hypersonic flight regime at Mach no 9.1 is carried out.While analyzing the Blunt, Slender, Snap and Pan shaped spikes, it is noticed that by introducing Blunt spike there is 13% reduction of heat at the nose, slender spike is around 7.5 %, Snap spike is around 11% and Pan spike is around 9.5% when compared with the without spike model.Finally, it can be concluded that as a result of spikes heat is reduced at nose

Figure 1
Figure 1 2D geometry of blunt body Solid works 2016 modeling software has been used for constructing the appropriate 3D model with available dimensions.This can be done by revolving the geometry about the center line as shown in the figure 1.The Domain is created by using ANSYS FLUENT 17.2 Package.The face of the domain is extended by 1.25l and behind the geometry by1.5l times.The top and bottom of the domain are enlarged by 1.25l times, where l is the major length of the geometry model .i.e.131.9mm.

Figure 2 Figure 3 2 ) 2 Figure 4
Figure 2 Mesh Model of the vehicle

Figure 5
Figure 5 Temperature Plot of Blunt Body

Figure 6
Figure 6 Contrast of Experimental Result with analytical result.

Figure 7 .
Figure 7. Heat transfer plot for the experimental model.

Figure 22 Figure 23 Figure 24
Figure 22 Temperature Contour of Pan Spiked Vehicle

Figure 25
Figure 25 Temperature Comparison of Blunt, Slender, Snap and Pan and without spike vehicles.