Analysis on Venting Time of Rarefaction Wave Gun

JOURNAL OF CHINA ORDNANCEAnalysis on Venting Time of Rarefaction Wave GunWANG Ying-ze( 王颖泽), ZHANG Xiao-bing(张小兵), YUAN Ya-xiong(哀亚雄)School of Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, ChinaAbstract: Based on the operation principle of rarefaction wave gun, the sletion and calculation methods for ventingopportune moment are invastigated. Considering property of the rarefaction wave, talking the center of muzzle section asinitial calculation point, supposing that at the moment projectile arrives to the muzzle, the rarefaction wave arrives to thebase of projectile, the rarefaction wave veloity along the barrel can be obtained by ftting calculation of the interior bllis-tic data of the same closed gun and reverse deduction. And then, the optimal venting time can be found out correctly basedon the rarefaction wave velocity.Key Words: interior bllistics; rarefaction wave velocity; venting mode; venting timeCLC Number: T]303* .4; TJ012.1*5Document Code: AArticle ID: 1673-002X(2008)04-0241-06to RAVEN. Earlier venting results in a change ofIntroductionmuzzle velocity and later venting lacks enough capaci-Currently, armament systems are developing to-ty to reduce the recoil and barrel heat.wards the informational, light and automatic direc-According to fluid dynamic laws, the rarefactiontions along with the development of military science.wave velocity is sum of the combined gas velocity andThe extreme lethality of the future combat systemthe local sonic speed. Because the combined gas veloc-program requires innovative armament solutions to ity is affected by venting time and venting mode itscircumvent traditional engineering barriers. Rarefac-calculation is very complicated. In this paper, sup-tion wave gun ( RAVEN) propulsion constitutes apose that when the projectile arrives to the muzzle,novel armament technology inspired to meet the re-the rarefaction wave front arrives to the base of thequirements of the Army' s Objective Force. It isprojectile. Based on this assumption and the propaga-based on a simple premise that a rarefaction wave cantion characteristic of the rarefaction wave, the rar-not propagate faster than propagation media move-efaction wave velocity in the barrel is obtained by re-ment and sonic velocities'1l, Thus, a gun system de-verse calculating for the interior ballistic process, andsigned to vent in the breech end of the chamber afterthen the accurate venting time is also found out.the projectile has begun its travel along the barrel will1 Choices of Venting Moderelease a forward traveling rarefaction wave. If therarefaction wave front has not caught up the base ofFor RAVEN, the venting time of venting de-projectile until it exits the muzzle, the recoil and bar-vices can be determined differently for the differentrel heat can be reduced significantly without affectingventing modes.the projectile movement. Therefore the venting op-1.1 Basic Requirements for Venting Deviceportune moment and venting mode are very importantBecause the recoil impulse and barrel heat can beReceived 2007-08-28Sponsored by Program for New Century Excellent Talents in University (NCETO中国煤化工-toral Program of HigherEducation (20060288019), and the Nrtional Nature Science Foundation of jiangsu PrBlographles WANG Ying xe(1981-), doctoral student, wy23701320@hotmail.TYHC N M H Gessor, zhangxb680504@163.com一241一JOURNAL OF CHINA ORDNANCE, 2008, Vol.4, No.4reduced significantly by the rarefaction wave propul-ber pressure is up to a pressure larger than the peaksion, the thickness of chamber and barrel is thinnerpressure of the disk, it will blast swiftly. Such disksthan that of traditional closed-chamber gun， thecan not be directly applied to RAVEN propulsion, asweight of the RAVEN is very light. If the ventingthe venting must be delayed. However, a disk de-devices can not operate in interior ballistic process,signed to withstand peak pressure without rupturingthe effect of RAVEN will be affected and even itand rupture at a predetermined time can be em-leads to chamber blast. In order to avoid dangerousployed.accidents, the venting device design must meet the2 Calculations of Rarefaction Wavefollowing requirements, i. e.Velocity and Venting TimeIn a launch process, the calculations of combinedgas velocity and local sonic speed are very complicat-ed, because propellant combustion, projectile move-ment and gas flow. As a result, it is very difficult tofind out the accurate venting opportune moment. AnFig.1 Image of a inertial breehengineering solution is to estimate the venting time by1) venting device must be steady and reliable;empirical formulas, and then, modify this venting2) nozzle area must be reasonable;time by experimental data. Although such method3) venting process must be swift;can usually meet engineering requirements and even4) nozzle must withstand ablating and eroding;be precise, its time consumption and expenditure are5) effect on the projectile velocity must be small.very large. In this paper, considered that the rarefac-1.2 Venting Modestion wave can not affect the property of medium thatThe stabilization and credibility of the ventingthe rarefaction wave front has not arrived, the veloci-devices depend on the venting modes and the reason-ty of the rarefaction wave and the accurate ventingable choice of venting mode affects the property oftime can be found out by utilizing the data of theRAVEN directly. Although there are lots of ventingsame type closed-chamber gun in fitting calculation.modes, including inertial breech actuator, cam ac-,vent chamberbarel procciletuator, gas-operated devices, detonated rupture diskand computer controlled' actuator, only the inertialbreech actuator and detonated rupture disk can meetthe above requirements mentioned above.、inertial breech^ cone1) Inertial breech actuator、 nozzleThe most widely recognized form of an inertialFig.2 Schematic pictare of a blot- operated RAVENbreech is Davis gun. It may be employed to open an2.1 Basic Assumptionsexhaust port behind the chamber timely in a similar1) The section change between the chamber andmeans with that a two-stroke engine uncovers its ex-the barrel can be ignored, and the distribution of gashaust port. Because this device is directly driven byvelocity in the barrel is linear according to Lagrange' sthe same propellant gases that are concurrently driv-hypothesis.ing the projectile in the barrel, it can meet the re-2) In consideration that the change of the tem-quirements of stabilization and credibility.perature distribution in the barrel is very small, the2) Detonated rupture disklocal中国煤化工y the average tem-The Germans, in their development of recoillessperatYHCNMHGed..artillery, employed this device first. When the cham-3) In consideration that the recoil impulse main-一242一WANG Ying-ze, et al. / Analysis on Venting Time of Rarefaction Wave Gunly applies to the inertial breech before venting, the ef-The following empirical formulas4] can be usedfect of the system recoil on the gas velocity in the bar-for estimating the venting timerel can be ignored.rRT(3)2.2 Interior Ballistic Modelu,=ug+c= 2u+ 11-ope'The venting method and interior ballistic processtg= tei-FtexinLe，(4determine the venting time and velocity of rarefactionrRI'vave.The interior ballistic equationsbsJ about2*0+ N1-0P。RAVEN arewhere V, Ug and Vp are the velocities of rarefactionwave, combustion gas and projectile respectively, tεlz =and texit the venting time and the exiting time, c theat~z>1,local sonic speed and L。the length of the barrel.lp_2.3.2 Experimental method to determine ventingtimedup. So边Considering the complexity of exactly acquiringdt Ppmp'the venting time, it is necessary to carry out some ex-dla_ |ub， p≥Pεvla≤lgperiments for rarefaction wave gun based on empiricaldtformulas.= qbm i’Sibep≥Pgvln≤lg,The experimental determination of exact ventingwas carried out by Benet labl5] based on the empiricall0,formulas. Fig. 3 shows its venting devices. The cor-(1-r)(x+2xhz)肾-θresponding distribution of the rarefaction wave veloci-ty is shown in Fig.4.dt 业-ηA(。duduxl(PpmpDp dt + 9ibmbUb dt81.00 .1.0000561.9822.125]7.797.000J e2Sz2|.82.9613.266 15° type Mdn。.w\p≥pε.free recoiltubing(1)1.5°typeL tubing31309-3.(业=xx + xz2,fwr(业一》)31309-1 31309-231309-2P= S,(q+(p) + Saln'(2)Flg.3 Venting device for experiment(l+=0[1-含(1-4)-a0(φ-n)],It can be seen from Table 1 that the empiricalwherelia, Vb, Sb，mab, lε and PE are the travel,formula for calculation can meet the engineering re-velocity, section area, mass, maximum travel andquirements, and the empirical formulas have somedriving pressure of the inertial breech respectively,guiding significance for engineering practice and ex-Sz the section area of the muzzle, Pp and Pib the fric-perimental method about the venting time.tional lost coefficients, τ the non-dimensional tem-2.3.3Fitting calculation for the rarefaction waveperature, η the non- dimensional opening flow, lo thevelocityshrinking length of the chamber, 0 the loading den-In order to avoid repeat validating above empiri-sity, δ the propellant density, a the covolume, and fcal formulas. the velnritv nf the rarefaction wave canthe propellant force.beca中国煤化工of the same type2.3 Calculation of Rarefaction Wave Velocityclosed:TYHC N M H G accurate venting2.3.1 Empirical formulas on venting timetime of RAVEN can be determined also. Based on the一243-JOURNAL OF CHINA ORDNANCE, 2008, Vol.4, No.44.5Taking x1 as 25% or 33%，the calculated mass- flered presure dat400, 4thorder polymomial ft.0of inertial breech is 20.5 kg or 35.9 kg.3.5. rarfaction wave frort detocti300-- 2nd order wive front ft3.02) Calculation process250As shown in Fig. 5, taking the muzzle plane asthe initial calculation plane, and Ot as a time step,150-100thus the initial velocity of rarefaction waveis ur=(vg+5o-c)texit， and the rarefaction wave traveling displace-ment Ol= v,Ot att- Ot time, and then the velocityin this time v,(t - Ot)=vg(t- Ot)+c(t-Ot)=.0一(v,(t- 0t)-ub(t-0))[1c(t)0t .. projcile travelLg- vp(t)Ot -.5- --- rarefactin wave-frontv1(t - Ot) + c(t - Ot). Repeat above calculation+ projecile 35.1% oftravel0 + release at 2.85 msunil 20l-(t-nOt)>= Lg, and then the time七shot-exit at 4.64 ms~1.s.tg=tmn一习Ot will be acurate venting time.0f>s-t/msFig.4 Pressure and travel distributions of 35 mm gunoperation principle of the inertial breech actuators,the venting time can be decided by the mass, travel-Fig.5 Calculation modeling displacement and driven pressure of inertial3 Analysesbreech.Based on ftting of the interior ballistic data of 35mm Oerlikon KD series gun, the distribution of theTable 1 Comparison of venting time between empiricalformulas and experiment resultrarefaction wave velocity and synchronous ventinggun typeM256/M829A2 M1/Oerikon time for 35 mm TP RAVEN system are found out.caliber/ mm201) Fig. 6 and Fig. 7 show the velocity distribu-venting time (experiment)/ms.72.85tion and synchronous venting time respectively for theventing timeinertial breech mass of 35.9kg. It can be seen that.92.65(experiential formula)/msthe contribution of the combustion gas velocity and2000error (ime)/%7.4-7.01 800一RAVEN velocity1 600- - sonic velocity--- gas velocity1) Selection of inrtial breech' s mass1 400It can be seen that the opportune moment of is12001000within a range in which the projectile travels to 25%800-- 33% of the barrel based on the tests for different600RAVEN systems. Thus, from the formulasl4, the200mass of the inertial breech can be found out-20004.i.smb°(到"(m。+置叫中国煤化工Ublx=25% - 3%’'D./4MYHC N M H Gedity dsribatitoiosUb= (tax- tpmx)/10(5)(mp=35.9 kg)一244一-WANG Ying-ze, et al. / Analysis on Venting Time of Rarefaction Wave Gunlocal sonic speed to rarefaction wave velocity froment breech velocity and combined gas velocity distri-Fig.6. In Fig. 7, the synchronous venting time isbution, the velocity of inertial breech is much slowerabout 2.55 ms, while the projectile travels 32.2% ofthan the projectile velocity, thus, its influences onthe barrel length.the gas velocity and local sonic speed are much small.3.50- projectile travel3..5-- RAVEN tavel2.- RAVEN travels 2.0号1.5-.0F1.0-.5-0.5t/msFig.7 Proectile, RAVEN travel distributionsFIg.9 Projectil, RAVEN travel distributions(mn=35.9kg)(mm= 20.5 kg)2) Fig. 8 and Fig. 9 show the velocity distribu-2 00tion and synchronous venting time respectively for the1 800inertial breech mass of 20.5 kg. Compared to Fig. 61 6001 400and Fig.7, it can be found that the velocity dstribu-1200tions are almost the same except a slight difference inn 1000venting times. In Fig. 9，the synchronous venting昌800. RAVEN velocity 1600.... sonic velocity 1time is about 2.5 ms, while the projectile travels to400. . gas velocity i31.7% of the barrel length.200---- RAVEN velocity 2... sonic velocity 2... gas velocity 21 800-2025 t.03.5 44.5,01 400-Fig.10 RAVEN, sonie and gas velocity distributions百1000under different breech masses00-0o4) Fig. 11 shows the comparison between calcu-lated and experimental results. It can be seen that the00.-- gas velocity. rarefaction wave velocity(calculation)+ rarefaction wave velocity(experimenl)3.05.0---- projectile velocity(calculation). projectile velocity(experiment)Flg.8 RAVEN, sonic and gas velocity distributions。2.03) Fig. 10 shows the velocity distributions for in-ertial breeches of 35.9 kg and 20.5 kg. The distribu-tions of the combined gas velocities and rarefaction0.wave velocities are similar and the local sonic speed中国煤化工一4distribution is almost consistent. The reason lies onthe operation principle of inertial breech devices. Al-.MYHC N M H GAVEN tnavel ditrirethough different inertial breech mass results in differ-tios between the calculated and the experimented一245一JOURNAL OF CHINA ORDNANCE, 2008, Vol.4, No.4calculated results about the velocities of projectile andcalculated venting time is less than experiment result.rarefaction wave are very close to the experimental re-But the calculated percentage of projectile travel issults.close to the experiment result. Therefore, it is feasi-5) Table 2 shows a comparison of venting timeble to find out the venting time by calculation of thebetween the calculation and experiment results. Therarefaction wave velocity .Table 2 Comparison of venting time between the calculated and the experlmented35 mm TP RAVEN gunventing time/ msexiting time/ms projectile route percentage/ %errorexperinental reult (ma= 35.9 kg)2.854.64experimental reult (ma=20.5 kg)2.804.6932.3this paper (ma= 35.9 kg)2.554.5532.2-10.5this paper (ma=20.5 kg)2.504.6031.7- 10.7[R]. ARCCB- TR-02001, AD-A398942, 2002.4 Conclusions[2] Kathe E. Sonic rarefaction wave rollss gun system,Based on the operation mechanism of RAVEN,US: Patent Application 6460446[P]. 2000-08-02.supposing the moment the rarefaction wave front ar-[3] YUAN Ya-xiong, ZHANG Xiao-bing. Muliphase hy-rives at the base of projectile at the moment that thedrokinetic foundation of high temperature and high pres-projectile arrives to muzzle, the rarefaction wave ve-sure[ M]. Harbin: Harbin Institute of Technology Press,locity traveling along the barrel can be calculated by2005. (in Chinese)fitting the interior ballistic data of the same typ[4] Kathe E, Witherell M, Dillon R. Rarefaction wave gunclosed gun. And then the venting time can be obtained.propulsion [ R]. ARCCB-TR-02001， AD-A389156,2001.References[5] Kathe E. Rarefaction wave gun propulsion[D]. Troy,[1] Kathe E, Dillon R. Sonic rarefaction wave low recoil gunNY: Rensselaer Polytechnic Institute, 2002.中国煤化工MYHCNMHG一246一