A88-44710 # Accelejating projectiles up to 12 km/sec. utilizing th continuous detonation propulsion method. Josef Rom (Technion - Israel Ins tute of Technology, Haifa) and Yosef Kivity (Rafael Armament Developme Authority, tiaiia, Israel). AIAA, ASME, SAE, and ASEE. Joint ems, 24th. Boston, MA, July 11-13, 1988, AIAA Paper 88-2969. 7

The chemical energy of a preloaded, pressurized !uel/oxydizer tube can be utilized for the continuous acceleration of projectiles. Thi by firing such properly shaped projectiles at sufficiently high initial the tube filled with the premixed gas so as to enable the generatio sonic flow field including detonatron waves which result in generati tht zzt. In the 'ram accelerator' this is achieved by reflections

the tube wall. Such interaction can be avoided ahen the 'external propulsi method is used. The present paper presents a method for preliminary evaluat of the performance characteristics of such systems with particular reference enhancement of the performance by 'tailoriny' the fueVoxydizer mixture and t geometrical shape of the tube in the 'ram accelerator' mode of operation.

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ACCELERATING PROJECTILES UP TO 12 KM/SEC. UTILIZING THE CONTINUilUS i3ETONATIi)N PROPULSION METHOD

4

Josef Rom and Yasef Kivitv

Abstract

The chemical energv of a preloaded. pressurized fuel/oxvdizer mixture in a tube can be utilized for the continuous acceleration of projectiles. This is achieved bv firing such properlv shaped projectiles at sufficiently high initial velocitv inta the tube filled with the premixed gas so as to enable the generation of a supersonic flow field including detonation waves which result in generating positive thrust. In the "Ram Accelerator" this is achieved by reflections of the waves from the tube wall. Such interaction can be avoided when the "External Propulsion" method is used. The present paper presents a method for preliminarv evaluation of the performance characteristics of such svstems with particular reference to enhancement of the performance by "tailoring" the fuel/oxvdizer mixture and the geometrical shape of the tube in the "Ram Accelerator" mode of operation.

List of Symbols

acceleration. speed of sound projectile maximum cross-section area gravitational acceleration acceleration parameter pressure heat addition due to chemical reaction gas constant temperature pro~ectile velocitv velocity components normal and parallel to the oblique wave.

Introduction

It is the aero-propulsion dream to produce thrust by aerothermal processes utilizing the vehicle shape as part of the propulsive process. With the advent of hvpersonic flight, in the 1950's and the 1960's. various designs for "external propulsion" were proposed. These are discussed by Kuchemann in Ref. 1. These schemes failed in actual practice because the rate of mixing of the fuel with the flowing air is relatively slow. Therefore. the required homogeneous fuel/air mixing is not completed within

* - Lady Davis Professor. Faculty of

Aeronautical Engineering. Technion - Israel Institute of Technology, Haifa 32000. Israel. Fellow AIAA.

* * Research Fellow. RAFAEL

the va:hicle length. In such a case. the supersonic combustion or detonation cannot be sustained in the proper position on the vehicle.

A breakthrough idea for propelling projectiles utilizing the ram cycle was presented by Prof. A. Hertzberg and his coworkers at the Universitv sf Washington. Refs. 2 - 8 . The concepts of the Ramjet-in-Tube for subsonic and supersonic combustion and the detonation wave modes of operation are illustrated in Figs. la to Id. Some of the results reported in Ref. 7 are shown in Fig. 2. Projectile velacitv of atlout 200il mis were achieved in a 11 m long tube with the choked subsonic combustion mode cf operaticln .

The ramjet cvcle requirss reflecticlns of the shocks from the tube walls. So. as the proiectile speed increases. the pressure behind the reflected shocks is multiplied to verv high values requirins high strength tube walls to cantain the process. The nose shock wave is reflected as a detontj~ion wave when the svstem is clperatea ir che continuous detonation mode. The highest thrust wlll be obtained if this (ietonation wave intersects the projectile on the corner between the nose and the afterbody cones. Since the shock wave and detonation wave angles become shallow as the projectile Mach number increases. therefare, the optimum size of the projectile increases with projectile speed for a fixed tube diameter. Or for a fixed projectile diameter increased thrust and propulsive efficiencv can be obtained bv reduclng the tube diameter in accordance with the speed increase of the projectile. This can be achieved bv the conicallv tapering of the internal diameter, ~ . r . a number of tubes of reduced diameter car, be arranged in a stepped system to improve the performance with a simpler geometrical arrangement.

This improvement in performance is obtained in addition to the increased efficiency which is achieved by tailoring the gas mixtures - introducing more energetic mixtures into tube sections as projectile speed increases as suggested in Ref. 2. Increased efficiency can be achieved also by tailoring the tube diameter - either by use of smaller diameters far tube sections or bv the proper tapering of the internal diameter as the projectile velocity increases. The advantages of the tailoring of the tube geametrv will be discussed in this paper.

At higher speeds the operation mode

t- - 1 L 1REPR -- OOR

must depend an detonation waves. as seen ~n Flg. Id. At these flight conditiox 1 t 1s pc~sible t c ~ utilize the principles c+f the "external propulsion" to contlnuouslv propel the prolectile to hlgher speeds instead of the ram?et-in- tube cvcle prc~posed by Hertzberg et al. T h i s met hcld of propulsion does not require anv lnteraction with the tube wall. Actuallv the tube can be made as large as desired, so that the strength of the shocks. which are generated on the vehicle. are reduced bv the time thev Intersect with the tube walls.

Method of Operation

The operational svstem requires two stages: an initial acceleration stage and the external propulsion launch tube. The initial acceleration can be achieved by artlllerv powder charge capable to accelerate the projectile to high supersonic velclc ities . With known high velocitv powder technology, peak velocities of 17uu-200il rn/s can be achieved. enabling direct utilization of the aetonation mode of operation. Otherwise. utilizing the subsonic Ram Accele~ation mode it is possible to bring the prajectile to about 200U-2200 m/s and then to establish the detonation mode for further acceleration. The speeding projectile then penetrates the launch tube which is filled with proper fuel/oxvdizer mixture and is further accelerated to higher velocities as it travels down the tube bv the continuous detonation process until it exits from the tube having reached its maximum launch velocity. A schematic diagram of this svstem is presented in Fig. 3.

Preliminary Performance Calculations

As a first step in the evaluation of the performance of the continuous detonatlon propulsion, a simplifed model is used The flow 1s assumed to be planar, with plane shock waves and detonation fronts. The gas mixtures are assumed to behave as ideal gases with constant coefficients except that there 1s a discontinuous Jump of the specific heat ratio across the detonation front. The detonation front is assumed t~ be stabilized at the Chapman-Jouguet condition. In some cases the overdriven GI-:onation wave is allowed, then boundary conditions determine the detonation conditions. In these calculations all effects of viscositv and heat conduction are neglected. Using these assumptions snables to establish a relatively simple one-dimensional type calculation scheme.

The flow field is shown in Fig. 4. The incoming undisturbed flow is defined as state 1. The oblique shock wave attached to the projectile tip compresses the gases to state 2 . The reflected wave from the tube wall heats the gases to temperatures above the detonation limit and a CJ detonation wave is established,

defining the state 3 behind the CJ detonation. The flow deflection by the detonation wave may require an expansion wat- to turn the flow parallel to the vehicle cylindrical part. The flow in the cvlindrical portion is assumed to result in co~ditions of flow parallel to the cvlindrical bod\'. defined as state 4. Now, the flow is expmded in the conical back part of the vehicle to the exit conditims, defined as qtate 5. The expansion conditions can be evaluated assuming a quasi one-dimensional duct flow. so the net thrust is equal to the momentum gain between the outgoing momentum in state 5 and the incoming momentum of state 4. Another option available in the calcuation scheme is based on a Prandtl-Meyer expansion fan from state 4 to state 5. The thrust is calculated from the evaluation of the net pressure forces acting on the vehicle. The governing equations for the oblique wavp systems are the usual conservation equations. while those for the oblique detonation wave are:

The solution of these equations. including calculatims of the chemical ieactions and the properties of the gases, enable the evaluation of the performance parameters.

Performance Characteristics

Acceleration in a straight tube

The results of the calculations described in the previous section enable the evaluation of the thrust generated on the projectile. The projectile acceleration can be determined by the ratio of the net thrust to the projectile weight. The variation of the acceleration parameter - G=p *(A/WIL(a/g) - as a function of the projectile velocity is shown, for various flow configurations, in Fig. where p is the gas mixture initial pressure. A/W is the ratio between the projectile maximum area A, and the projectile weight W , and the acceleration a normalized by the earth gravity constant. The calculations are performed for two conical forebodies - 4 and 8 nosecone half angles and for

mixtures of Methane-Air and Hydrogen- vxvgen. The velocitv range is between 2 km/sec to 12 km/sec. In order to assure the proper flow field and wave reflections as the projectile velocity increases, a cvlindrical midsection is introduced on the projectile. as seen in Fig. 4. The length of the cylindrical section depends on the required speed range. This cylindrical section can be short if the tube diameter is varied as the projectile speed increases.

One of the requirements is that the temperature behind the nose shock wave (zone 2 in Fig. 4) will be below the detonation temperature of the mixture. in order to avoid the undesirable detonation of the gases before the reflected shock, while determining that the temperature in zone 3 in Fig. 4 is above the detonation limit. These conditions are plotted in

Figs. 5a and Sb, for 4" and 8 O noses. respectively.

The acceleration parameter G=p *cA/W)*(a/g) variation with projectile speed for a constant area tube is shown in Fig. 6. The acceleration decreases as the projectile speed increases. Similarly, the propulsive efficiency. which is showq in Fig. 7 also decreases with speed. The performance can be improved by dividing the tube into two or more sections and introducing higher energy mixtures in the downstream sections where the velocities are high. The effects of a combination of Methane- Air in the first section and 2H2+02 in

the downstream section is also shown in Figs. 5.6 and 7 . The advantage of such tailoring of the gas mixtures to increase the efficiency of the process and the projectile acceleration is obvious from these results. and were previously described by Hertzberg et al. in Refs. 2-8.

Acceleration in a fitted tube

An additional means for tailoring the system to increase the propulsive efficiency and acceleration is by fitting the tube diameter as the projectile velocitv is increased. This can be done by a discontinuous change in tube diameter in steps, thus dividing the tube into sections. Or, by a continuous change in tube diameter, resulting in a gradual tapering towards the muzzle. The performance of the fitted barrel svstem is presented in Figs. 6 and 7 for a velocity range of 2 to 5 Km/s, and in Figs. 8 and 9 for a wider velocity range .of 2-12 Km/s. It is seen that the fitted tube can increase the acceleration considerably. In particular it allows a much wider velocity range with a single mixture.

A very pronounced effect due to lowering the nose cone angle is observed. The results of the 4 half cones indicate

that this projectile will have better acceleration and reach higher speeds than the one with 8 half cone angles. Both results are shown in Figs-ba and 8b, and 9a and 5b.

Concluding Remarks

It is shown that a projectile traveling at supersonic-hypersonic speeds in a tube filled with a gaseous mixture of fuel /oxydizer is capable of generating thrust either by the Ram Accelerator mode of interaction with the tube wall or in the external propulsion mode of operation. Already the simplified analysis based on the one-dimensional flow field indicates the important effects of the gas mixture. the ratio of the projectile, diameter to the tube diameter and the slenderness ratio of the projectile on the thrust and propulsion efficiency.

It is clear that this method of propul-sion has many important applications and in particular in space flight. The direct utilization of the chemical energy for continuous propulsion to high speeds has many advantages over those systems based on electro-magnetic or electro-thermal drivers since the energy density of chemical storage is so much greater than the electric and magnetic systems.

References

Kuchemann. D.. The Aerodynamnic Design of Aircraft . Pergammon Press. 1978.

Hertzberg. A., Bruckner. A.P. and Bogdanoff. D . W . , "The Ram Accelerator: A New Chemical Method of Achieving Ultrahigh Velocities", Presented at the 37th Meeting of the Aereballistic Range Association. Quebec. Canada. Sept. 1986.

Hertzberg. A., Bruckner. A.P. and Bogdanoff. D . W . . "The Ram Accelerator: A New Chemical Method for Accelerating Projectiles to Ultrahigh Velocities", AIAA Journal. in press.

Bruckner, A . P . , Bogdanoff, D . W . , Knowlen, C. and Hertzberg. A., "Investigations of Gasdynamic Phenomena Associated with the Ram Acdelerator Concept", AIAA Paper 87-1327, June 1987.

Knowlen, C., Bruckner, A.P.. Bogdanoff, D . W . and Hertzberg, A . . "Performance Capabilities of the Ram Accelerator". AIAA Paper 87-2152, June 1987.

S POOR

.

5 . Bogdanof f . D. W. and Brackett . D.C.. "A Computational Fluid Dvnamic Code for the Investigaltion of Ramjet-in- Tube Concepts". AIAA Paper 87-1978. June 1987.

7 . Hertzberg, A.. Bruckner, A.P.. Bogdanoff D.W. and Knowlen. C . . "The Ram Accelerator and Its Applications: A New Chemical Approach for Reaching Ultrahigh Velocities". Presented at the 16th International Symposium on Shock Tubes and Waves, July 1987.

8. Bruckner. A.P. and Hertzberg. A.. "Ram Accelerator Direct Launch System for Space Cargo". Paper No. IAF-87-211. 38th Congress of the International Astronautical Federation, October 1987.

Acknowledgements

The detonation characteristics of the various gas mixtures were obtained uslng a chemical equilibrium c ~ d e . CJGAS, wrltten t ~ y Dr. D. Halevy of RAFAEL. The authors thank Dr. Halevv for his help in the calculations. The authors wish to acknowlege special thanks to Mr. Avidar Kivity for his help in developing the computer code for the interactive calculations of the CDP performance.

2000 , I I 1 I I 1 a E X P E R I M E N T

- THEORY

-

TRANSITION

I I I

Fig. 2. Velocity of projectile in the 11 m Ham Accelerator of U. of Washington (Ref. 7).

F i g . 4. The Flow Field with Oblique Detonation.

N O R n A L SllBSONlC CHOKE ACCELERATOR BARREL SHOCK COnBUSTlON POINT

THEWlAL CHOKING

POINT

ACCELERATOR BARREL SHOCK

BOW SHOCK ' ,'

. . -. PREMIXED .-.

2 3 4 5 I ,

6

(bj OVERDRIVEN DETONATION

WAVE

A NORMAL REACTION CHOKE

ACCELERATOR BARREL SHCCK ZONE POINT

pREnlxED ---.-..a, FUEL I OXIDIZER

OBLlClJE DETONATION

ACCELERATOR BARREL WAVE

Fig. 1. The Ham Accelerator propulsion configurations (ne~. 2)

~ a u n c h gun Premixed f ue 110xidizer m i x tu re

D i aphragm E x i t diaphragm

Fig. 3. The H~pervelocity Launcher Concept.

REPRODUCIBILITY 4

EFFICIENCY

0-25 I METHANEtAIR, FITTED BARREL

Vkm /sec

Fig. Sa. The temperature behind the Nose Shock Wave and the pressure behind the Refiected Detonation Wave for the 4 half angle Cone Projectile.

V km /see

Fig. 5b. The temperature behind the Nose Shock wave and the pressure behind the Reflected Detonation Wave for the 8O half angle Cone Projectile.

-m

DIAMETER BARREL

Fig. 6. TGe Acceleration Figure for a 8 Projectile in a Uniform Diameter Tube with Methane-Air and additional 2H2+02 section

in comparison with the Fitted Barrel design.

UNIFORM BARREL

Fig. 7. The Propulsion Efficiency for the Uniform and Fitted Barrel cases.

Fig. 8a. The Acceleration Figure for Methane-Air and ZH2-O? in a

Fitted Barrel for a 4 half angle cone projectile.

Fig. 8b. The Acceleration Figure for Methane--Air and 2H2-O2 in a

Fitted barrel for a 8 half angle cone projectile.

Fig. 9a. The propulsive efficiency for a Methane-Air and 2H tO in a ? Fitted Barrel for a 4 half angle cone projectile.

I I I I L A d 3 4 5 6 7 8 9 1 0 1 1 1 2

V km /sec

Fig. 9b. The propulsive efficiencv for a Methane-Air and 2H +O in a z Fitted Barrel for a 4 half angle cone projectile.

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