Aerodynamic Heating

Numerical Investigation on Aerospike Induced Flow Field on Blunt Bodies at High Mach number

Submitted in partial fulfillment of the requirements for the degree of Master of Technology by Ayyappankutty k m

Supervisor Dr Tide p s Dr. Saju k s

Division of Mechanical Engineering Cochin University of Science and Technology, Kochi-22 2014

Contents Chapter 1

Introduction

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2

Literature Review

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2.1 Aero spike induced flow field

4

3

Problem description

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4

Methodology

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4.1 Governing equations

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5

Early Results

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6

Future plan

8

7

References

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Chapter-1 Introduction: High-speed flow past a blunt body generates a bow shock wave which causes high surface pressure and as a result the development of high aero dynamic drags. The dynamic pressure on the surface of the blunt body can be substantially reduced by creating a low pressure region in front of the blunt body by mounting a spike. The use of the forward facing spike attached with the shape of a hemispherical blunt body appears to be most effective and simple method to integrate the vehicle as compared with the focused energy deposition and telescopic aero disk . A blunt body creates a bow shock wave at high Mach number, which produces a very high in pressure in the forward region of the hemispherical region, which leads to an increase of high wave drag during the projectile’s flight through the atmosphere. It is advantageous to have a vehicle with a low drag coefficient in order to minimize the thrust required from the propulsive system during the supersonic and hypersonic regime. Aero-spike, energy deposition along the stagnation streamline, the forward facing jet in the stagnation pressure zone of a blunt body and the artificial blunted nose cone-out are studied numerically and experimentally to access the capability to reduce the aerodynamic drag. A typical flow over a spike attached to a blunt body is based on experimental investigations. A schematic of the flow field over the conical and the aero-disk spiked blunt body at zero angle of attack is shown in Fig. 1(a) and (b), respectively. The flow field around a spiked blunt body appears to be very complicated and complex and contains a number of interesting flow phenomena and characteristic, which has yet to be investigated. 1

Fig-1(a) Schematic sketch for flow field over conical spiked blunt body

Fig-1(b) Schematic sketch for flow field over aero disc shaped blunt body

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Chapter-2 Literature review Motoyama et al. [3] have experimentally investigated the aerodynamic and heat transfer characteristics of conical, hemispherical and flat-faced disk attached to the aero-spike for a free stream Mach number 7, free stream Reynolds number 4x105/m, based on the cylinder diameter. For L/D = 0.5 and 1.0, and angle-of-attack 0 to 8 deg, where L is the spike length and D is the cylinder diameter. They found that the aero-disk spike (L/D = 1.0 and aero-disk diameter of 10 mm), has a superior drag reduction capability as compared to the other aero-spikes Yamauchi et al. [4] have numerically investigated the flow field around a spiked blunt body at free stream mach numbers of 2.01, 4.14and 6.80 for different ratio of L/D Kamaran et al. [5]used a numerical approach to solve the compressible Navier-Stokes equations. The reattachment point can be moved backward or removed, which depends on the spike length or the nose configuration. However, because of the reattachment of the shear layer on the shoulder of the hemispherical body, the pressure near that point becomes large. Milicev et al. [6] have experimentally investigated the influence of four different types of spikes attached attached to a hemisphere-cylinder body at Mach number 1.89, Reynolds number 0.38x106The main purpose of the present study is to calculate surface pressure distributions and aerodynamic drag over the forward facing spike of various shapes at Mach number 6.The present paper presents a numerical simulation of the flow field over conical ,hemispherical and flat-disc aero spike attached to blunt body. The focus of the present numerical analysis is to investigate the based on the cylinder diameter, and at an angle-of-attack 2 deg. They observed in

their experimental studies that a reliable estimation of the aerodynamic effects of the spike can be made in conjunction with flow visualization technique. 2.1 Aerospike induced flow field. At low hypersonic speeds and angle of attack=0 a detached bow shock stands out in front of the aero disk and remains away from the dome. As the flow behind the bow shock expands around the aero disk, a weak compression is formed at its base. The wake flow caused by the aero disk and the nearly stagnant flow near the dome creates the conically-shaped recirculation region shown. The region is separated from the in viscid flow within the bow shock by a flow(fig-2) separation shock. This shock isolates the recirculation region which effectively reduces the pressure and heating distributions on the hemispherical dome and also allows them to be more uniform. Furthermore, this configuration has a body with a larger diameter than the dome, creating the potential for additional flow recirculation in the region near the front face of the body(referred to as the collar) and the side of the dome .For non-zero angles of attack, the flow field is further altered by a lee-side vortex structure that is influenced by the presence presence of the aero spike. The separated, vertical flow region in front of the dome is unsteady ,which may cause structural fatigue at the aero spike attachment region. Furthermore, the variation in model wall wall temperature during a tunnel run will affect the state of the aero spike boundary layer and subsequent separation shock at the foremost edge of the recirculation region. All of these phenomena may influence the dome surface aero thermal characteristics 4

Fig. 2. Schematic of aerospike-induced flowfield [1]

Chapter-3 3-Problem description: The aero spike model surface geometry is shown in figure 3[1] The material used for the model was 17-4 PH,H900 stainless steel. It consists of a 4-inch long, 4-inchdiameter cylindrical body and a 3-inch diameter hemispherical dome. The dome is offset from the body with a 0.25-inch long, 3-inch diameter cylindrical extension .The model design allows for the testing of the model with or without an aero spike, which is threaded at the base and screws into the dome. The aero spike as used in this series of tests consisted of a 12-inch long aero spike /aero disk assembly, hereafter referred to as simply ‘the aero spike

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Fig. 3. Aerospike surface geometry dimensions (in m). The test conditions are stagnation pressure of 475N/m2 ,stagnation temperature of 875K, Reynolds number of 8.0x106 and Mach number of 6.06 at the following angle of attack: 1 Feasibility Assessment at angle of attack = 0 2 Feasibility Assessment at angle of attack = 5 3 Feasibility Assessment at angle of attack =10 4 Feasibility Assessment at angle of attack =20 5 Feasibility Assessment at angle of attack =40

Chapter-4 4.Proposed methodology: The commercial software Ansys-Fluent14.0 is used for the numerical simulation of the problem. The steps involved in modelling are 1 Pre-Processing 2 Analysis 3 Post-Processing For pre-processing ICEM-CFD is used (Figure-4) The Discretization Method used is Finite Volume Method (FVM) 6

4.1 Governing equations: A numerical simulation of the unsteady, compressible, axi symmetric Navier-Stokes equations is attempted in order to understand the basic fluid dynamics over forward facing spike attached to blunt body. The governing equations can be written in the following strong conservation form:

(1) where W is conservative state and F and G are in viscid flux vectors, x and r are axial and radial coordinate system and t is time. The temperature is related to pressure and density by perfect gas equation of state as:

(2) The ratio of the specific heat is assumed constant and is equal to 1.4. The flow is assumed to be laminar, which is also consistent to Bogdonoff and Vas [7], Yamauchi et al. [4], Fujita and Kubota [8], and Boyce et at. [9].

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Chapter-5 Early results

Fig.4.Aerospike surface geometry dimensions (in m).(Angle of attack=0.

Chapter-6 6.1 Future plan: Analysis has to be carried out: (1) Steady state analysis with implicit formulation has to be carried out. (2) Pressure based coupled solver formulation will be chosen to obtain an accurate fast converging solution (3) k-ε turbulence model will be employed to simulate turbulence effects. Post processing has to be carried out: For post processing CFD-Post14.0 will be used 8

Chapter-7 References: 1 Lawrence D. Huebner.; Anthony M.Mitchell.; and Ellis J Boudreaux.: “Expiremental results on the feasibility of an Aerospike for Hypersonic Missiles” 33rd Aerospace Sciences Meeting and Exhibit January 9-13, 1995 / Reno, NV 2 R. C. Mehta; R. Kalimuthu ; E. Rathakrishnan .: “Flow field analysis over Aero-disc attached to Blund-Nose body at Mach 6” Proceedings of the 37th International & 4th National Conference on Fluid Mechanics and Fluid Power December 16-18, 2010, IIT Madras, Chennai, India. 3 Motoyama, N., Mihara, K., Miyajima, R.,Watanuki, W. andKubota, H, “ThermalProtection and Drag reduction with Use of Spike in Hypersonic Flow”, AIAA Paper 2001-1828, 2001 . 4 Yamauchi, M., Fujjii, K.,Tamura, Y., and Higashino, F.,“Numerical investigation of Hypersonic Flow Around a Spiked Blunt Body”, AIAA paper 93-0887, Jan. 1993 5 Kamaran, Davis H.: “Investigation of the Flow Over a Spiked-Nose Hemisphere-Cylinder at a Mach Number of 6.8,” NASA TN D-118, December 1959. 6 Milicev, S. S., Pavlovic, M. D., Ristic, S. and Vitic, A., On the influence of spike shape at supersonic flow past blunt bodies, Mechanics,Automatic Control and Robotics, Vol. 3, No. 12,2002, pp. 371-382. 7 Bogdonoff, S. M. and Vas, I. E., “Preliminary Investigations of Spike Bodies at Hypersonic Speeds”, Jr. of the Aerospace Sciences, Vol.26, No.2, Feb-1959, pp. 65-74.

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8 Fujita, M., and Kubota, H., “Numerical Simulation of Flowfield over a Spiked Blunt Nose”, Computational Fluid Dynamics Journal, Vol. 1, No. 2, 1992, pp.187-195. 9. Boyce, R., Neely, A., Odam, J., and Stewart, B., “CFD Analysis of the HYCAUSE Nose-Cone”, AIAA Paper 2005-3339, May 2005.

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