Research Article. Design of Nozzle and Fin Locking Unit for MRECM Rocket: A Study

Transcription

1 Internatinal Jurnal f Current Engineering and Technlgy E-ISSN , P-ISSN INPRESSCO, All Rights Reserved Available at Research Article Arjun Ogale *, Omkar Marathe, Saurabh Misal and Nitinkumar Anekar Department f Mechanical Engineering, MITCOE Pune, Savitribai Phule Pune University, Maharashtra, India Accepted 0 March 016, Available nline 15 March 016, Special Issue-4 (March 016) Abstract In view f the current strategic defense scenari f the wrld, specifically Asia, it is necessary t use mdern security systems in air, land and water. One f the slutins is t have air security blanket r dme in the frm f decy missiles t intercept incming enemy missiles. The current wrk was undertaken after the testing and analysis f the multi-nzzle stabilizer unit. A design fr a single nzzle unit fr the same rcket is nw required. This paper cvers the first half f a year-lng effrt which invlves cnceptualizatin and the initial design f the nzzle and stabilizing mechanism. Keywrds: Lift and drag, cnvergent-divergent nzzle, cmpressible flw, Mach number, weight reductin 1. Intrductin 1 A cunter-measure rcket is a decy rcket that is deplyed when an incming rcket is detected in rder t aggressively intercept it mid-flight t prtect the attacking rcket s riginal target. In rder fr tw rckets t cllide mid-flight, it becmes necessary t ensure that the flight trajectry f the cunter-measure rcket des nt deviate frm what is intended. Hence the need fr a rbust and precise stabilizer unit. The analysis and the results btained fr the stabilizer unit fr the Medium Range Electrnic Cunter Measure (MRECM) rcket can be used fr similar rcket systems with a few mdificatins in the design fr launching them frm varius platfrms. The incrpratin f a single nzzle in place f the six nzzles wuld significantly reduce the weight f the stabilizer unit as well as reduce the cmplexity f the stabilizer unit. T. Manivannan describe the design, analysis and develpment f fin lcking mechanism fr fin deplyment system. The design is based n a general fur-bar mechanism. Mukkane bring ut design f plan frm cnfiguratin f wrap-arund fins f a stabilizatin mechanism, theretical apprach fr estimatin f cant angle and spin. F.M.White describes in detail the thery f cmpressible fluid flw. Thrust frces and exhaust gas parameters have been defined by Suttn.. Frces n a rcket In flight, a rcket is subjected t fur frces; weight, thrust, and the Aerdynamic frces, lift and drag. The magnitude f the weight depends n the mass f all f *Crrespnding authr: Arjun Ogale the parts f the rcket. The weight frce is always directed twards the center f the earth and acts thrugh the center f gravity, the yellw dt n the figure. The magnitude f the thrust depends n the mass flw rate thrugh the engine and the velcity and pressure at the exit f the nzzle. The thrust frce nrmally acts alng the lngitudinal axis f the rcket and therefre acts thrugh the center f gravity. The magnitude f the Aerdynamic frces depends n the shape, size, and velcity f the rcket and n prperties f the atmsphere. These frces act thrugh the center f pressure. During the flight f a rcket small gusts f wind, r thrust instabilities can cause the rcket t "wbble", r change its attitude in flight. Like any bject in flight, a rcket rtates abut its center f gravity. The rtatin causes the axis f the rcket t be inclined at sme angle a t the flight path. Whenever the rcket is inclined t the flight path, a lift frce is generated by the rcket bdy and fins, while the Aerdynamic drag remains fairly cnstant fr small inclinatins. Lift and drag bth act thrugh the center f pressure f the rcket. The lift and the drag frces mve the nse back twards the flight directin nly if the center f pressure is lcated belw the center f gravity. In this case, they are called restring frces. On a cntrary, if the center f pressure is abve the center f gravity, the lift and drag frces maintain their directins but the directin f the trque generated by the frces is reversed. This is called a de-stabilizing frce. Any small displacement f the nse generates frces that cause the displacement t increase. Thus, ne f the main cnditins fr a stable rcket is that the center f pressure must be lcated belw the center f gravity. This principle is used while 347 MIT Cllege f Engineering, Pune, India, AMET 016, INPRESSCO IJCET Special Issue-4 (March 016)

2 determining fin area and weight f stabilizer unit. The fllwing line diagram indicates the different frces n a rcket in flight. cmpressin spring and three deplyment pistns. The pistns serve as an alternate deplyment arrangement in case the spring fails. Typically, rckets are kept in strage fr extended perids f time. It is due t this that the cmpressin spring used under the lcking ring might jam, causing the deplyment t fail. The alternate deplyment mechanism that uses pistns is activated by the frce generated by the burning prpellant. This cmbined cmpressin-spring-cumdeplyment-pistns system ensures a fail-safe way t deply the six stabilizing fins. The purpse f using a single central nzzle is t reduce the weight and cmplexity f the stability unit. The fllwing diagram shws the assembly f the new stabilizer unit. Fig. 1 Frces n a rcket 3. Design f Stabilizer Unit and Nzzle 3.1. Initial design f stabilizer unit The initial design f the stabilizer unit cnsisted f ne central nzzle surrunded by six peripheral nzzle, six fins and a lcking ring. All these parts were cntained within the nzzle blck whse uter diameter was the same as the diameter f the rcket bdy. The functin f the lcking ring is t ensure that all the six fins are deplyed simultaneusly as the rcket leaves the launching tube. The fllwing diagram shws the assembly f the ld stabilizer unit. Fig. Initial design f stabilizer unit It als functins t ensure that the fins stay deplyed at an angle f 45 nce they are pened. During deplyment, the lcking ring is pushed utward via a pistn by the frce generated by the burning f the prpellant. 3.. New design f the stabilizer unit The new design f the stabilizer unit fr the MRECM Rcket aims t replace the seven-nzzle system with a single central nzzle system. It cnsists f a nzzle blck, six fins, ne lcking ring, ne central nzzle, ne Fig. 3 New design f stabilizer unit 3.3. Prpulsin system design The impulse required by the rcket needs t be fund ut initially based n parameters like range f the rcket, mass f the paylad t be carried, drag cefficient etc. CFD analysis wuld prve very helpful in finding ut the abve parameters. The impulse is given as I T t 348 MIT Cllege f Engineering, Pune, India, AMET 016, INPRESSCO IJCET Special Issue-4 (March 016)

3 The required impulse can be achieved either by higher thrust fr shrt duratin r lwer thrust fr lnger duratin. Usually first apprach is preferred fr better fight stabilizatin. Based n the impulse required, the type f prpellant with requisite ballistic prperties is chsen. The physicchemical and ballistic prperties are btained by evaluatin f prpellant in ballistic evaluatin mtr (BEM are Based n the type f thrust required grain type is selected as thrust generated is directly prprtinal t mass flw rate f gases. In the mentined rcket we used a neutral burning type grain. The gemetry is hllw cylinder with inhibited ends. The graphs belw give the Thrust vs time and inner and uter radius vs time relatins Calrimetric value (Cal val) Characteristic velcity(c*) Specific heat rati (k) Burn rate (r) Pressure index (n) Temperature sensitivity (Πp) Specific impulse (I SP) BEM mtr firing at different chamber pressures is required fr finding temperature & pressure indices. The rate f burn f prpellant grain fllws the fllwing relatins r ap n Once fresaid parameters are btained the mass f prpellant t be used is decided based n specific impulse value (ISP). Mass f prpellant needed t btain required impulse will be I m I SP Then the prpellant grain is designed based n the chamber pressure required, dimensins f the rcket and type f thrust required. Grain design can be f three types: a. Neutral burning type in which the surface area f burning remains cnstant. b. Prgressive burning type in which the surface area increases with time. c. Digressive burning type in which the surface area decreases with time Design f nzzle Fig. 5 Thrust vs Time Accrding t Newtn s Third Law f mtin, ht exhaust gases which are accelerated using a nzzle prduce thrust n the rcket. The nzzle design gverns the pressure at the exit f the engine, mass flw rate thrugh the engine and the exit velcity f the flw which in turn decide the amunt f thrust generated. A cnvergent-divergent nzzle has been used in this case. The thrat size is calculated fr required chamber pressure and required thrust level. The value f the Mach number at the thrat is 1 i.e. the flw is snic. The gemetry diverges dwnstream and the flw expands isentrpically t a supersnic value f the Mach number which causes the static temperature and pressure t decrease frm the thrat t the exit. Thus, the exit temperature and pressure depend n the amunt f expansin. The exit temperature determines the exit speed f sund, which in turn determines the exit velcity. The exit pressure, velcity, and mass flw thrugh the nzzle determine the amunt f thrust prduced by the nzzle. Once the chamber pressure is knwn the thrat area f the nzzle is fund ut using the equatin: S ac At g P 1n (4) Fig. 4 Radius vs time Once the thrat dimensins are knwn, fllwing equatins are used fr gverning the lcal parameters in a nzzle: 349 MIT Cllege f Engineering, Pune, India, AMET 016, INPRESSCO IJCET Special Issue-4 (March 016)

4 Fr finding ut lcal temperature is given as, K 1 T 1 M T Fr finding lcal pressure is given as, k1 K 1 P 1 M P k It shuld satisfy the given impulse which is as givn in equatin (1). Thrugh iterative prcesses the given impulse requirements are met and then the design is cmpleted fr the nzzle. The fllwing graphs are prvided fr variatin f different parameters alng the nzzle fr ur design: Fr finding lcal density is given as, K 1 1 M Velcity f sund is given as, s K R T k1 Area rati is given as, k 1 k K 1 1 M A 1 At M K 1 1 Fig. 6 Temperature vs Mach N. Then the pressure rati t be maintained is decided since it cntrls the cefficient f thrust f the nzzle by the relatin is given as, k 1 k1 k 1 k k P e Pe P A e C f 1 k 1 k 1 P c P At Fig.7 Pressure vs Mach N. The length f the nzzle is decided by using trignmetric relatins where L tan Rexit Rthrat angle f divergence Where angle f divergence is kept belw 13 0 fr reducing flw lsses. If the length f the nzzle des nt fit in the design the exit pressure needs t be rewrked and crrespnding cefficient f thrust needs t be fund ut. Thrust C A P f t Fig. 8 Area Rati vs Mach N. 350 MIT Cllege f Engineering, Pune, India, AMET 016, INPRESSCO IJCET Special Issue-4 (March 016)

5 6. Nmenclature Fig. 9 Density vs Mach N. 4. Advantages and applicatins f MRECMR The advantages ver the previus stabilizer unit are given as, Thrust alignment with bdy axis. Reductin in cmplexity f the stabilizer unit. Reductin in manufacturing cst Reductin in skin frictin lsses. Applicatins f this Rcket are given as, The need fr this prject arse in the naval frces after electrnics were started t be used in guiding ffensive missiles t their targets. 5. Discussin Frm initial design f nzzle it can be cncluded that it is feasible t replace multiple nzzle prpulsin system with a single nzzle prpulsin system fr the required impulse which helps in keeping the skin frictin lsses t a minimum as skin cntact area reduces. The cmpnents f the initial design have been mdelled using the sftware Pr-Engineer. The newer design was dne in Slidwrks sftware. This design will nw be subjected t cmputatinal fluid dynamics analysis and field trials t check its rbustness at high air speeds. P 0 Stagnatin pressure ρ Density f prpellant ρ 0 Lcal density V Lcal velcity P Lcal pressure K Specific heat rati M Lcal Mach n T 0 Stagnatin temperature T Lcal temperature A Lcal area A e Exit area s Lcal speed f sund A t Thrat area I sp Specific impulse C f Cefficient f thrust M Mass P t Thrat pressure P e Exit pressure S Surface area N Pressure indices A Temperature indices K Specific heat rati C* Characteristic velcity R Burn rate I Impulse T Thrust T Time Acknwledgements We are grateful fr all the supprt given by ur head f department f Mechanical Engineering and the principal f MIT Cllege f Engineering, Pune. References Md. Shahid Quamar, T. Manivannan (001), Design, Analysis and Testing f Fin Lcking Mechanisms fr Fin Deplyment System f an Aircraft External Stre, ASMD S. B. Mukkane, K. J. Mane, S. M. Shelar, Dr. K. M. Rajan, (013) Design and Develpment f an Innvative Mechanism fr Deplyment f WAF Stabilizatin System fr an Artillery Rcket, ASMD. Jean-Pierrie, Bizien Rene, G. Patuilliart, Michel Gerge, (1976) Artillery Prjectile with Spreading Tail Assembly, United States Patent n. 3,944,168 F. M. White,(1999),Cmpressible flw, Fluid Mechanics, Internatinal editin, McGraw-Hill. Suttn, Oscar Biblrz, Rcket prpulsin Elements, 7 th editin, Wiley Interscience. Jadn V. K., Verma Suresh(010), Machine Design Data Bk, I. K. Internatinal Publicatin Huse, 351 MIT Cllege f Engineering, Pune, India, AMET 016, INPRESSCO IJCET Special Issue-4 (March 016)