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 1

2 Literature Review 3

2.1 Aero spike induced flow field 4

3 Problem description 5

4 Methodology 6

4.1 Governing equations 7

5 Early Results 8

6 Future plan 8

7 References 9

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

2

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

5

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].

7

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.

9

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.

10