H E UN IVE RS I TY OF M I CHIGAN College of Engineering Department of Nuclear Engineering Laboratory for Fluid Flow and Heat Transport Phenomena Technical Report, No. 010,gI1-T CURRENT STATUS OF GAS GUN. RAIN EROSION SIMULATOR S. T. Hinckley C. L.Kling R. Cheesewright F. G. Hammitt Financial Support Provided by: U. S. Naval Air Development Center Contract No. N62269-67-C-0631 August, 1967 NOT FOR FOREIGN DISTRIBUTION WITHOUT N.A.D.C. APPROVAL

ABSTRACT A review of the current status of work on a gas gun rain erosion simulator is presented, showing the various jet configurations and performance as a function of gun pressure which results. Unfortunately, with the present arrangement the data scatter is too great for the simulator to be used for ranking materials for erosion resistance. Modifications are discussed which it is hoped will reduce the scatter among the data to an acceptable level. -ii

CONTENTS Page Abstract —------------------------------------------- ii Introduction —---------------------------------------- 1 Present Results —------------------------------------- 2 Anticipated Technique Improvements —----------------- 3 Technique Modifications Previously Examined —--------- 4 Detailed Jet Characteristics —----- ---------------- 5 Bibliography —---------— 7 —------------------------ 7 Figures —--------------------------------------------- 8 -iii

INTRODUCT ION The current task in regard to the gas gun momentum exchange jet device is to standardize or systematize the techniques in which it can be used as a rain erosion simulation device. The 1,2 previous work' has been of an exploratory nature to examine different techniques which might give appreciably higher velocity jets or configurations more closely resembling a rain drop. This report discusses some of the variations that have been tried as well as variations presently under consideration. The emphasis of the present work is to determine that jet condition (form and size) which is most damaging. The most obvious damage criteria for single impact studies are pit depth and/or depth to diameter ratio. Therefore, samples of 1100-0 aluminum have been subjected to damaging impacts and attempts have been made to determine damage versus gun pressure in terms of these parameters as a function of nozzle size. However, the present results (Figures 1 and 2) show a great deal of scatter for tests involving nozzles of 1.0 and 1.8 mm diameter, respectively (nozzles 4 and 5). Hence, it appears necessary to improve the repeatability of the jet configuration. This can be evaluated more easily for the present in terms of jet and gun parameters rather than pit dimensions. -1

PRESENT RESULTS These considerations have suggested the following possible presentations of the data: Pellet Velocity vs. Gun Pressure Pellet Momentum vs. Gun Pressure Pellet Energy vs. Gun Pressure Jet Velocity vs. Gun Pressure as a function of nozzle diameter Jet Mass vs. Gun Pressure as a function of nozzle diameter Jet Energy vs. Gun Pressure as a function of nozzle diameter Jet Momentum vs. Gun Pressure as a function of nozzle diameter. The mechanical strength of the nozzles limits the maximum usable pressure at present to about 500 lbf/in. However, only the first three, which do not involve the momentum interchange between pellet and jet, show reasonable reproducibility and have not proved to be significant, presumably because of the large (up to 100%) variations in the jet characteristics under an apparently fixed set of conditions (Figures 3 through 9). Thus, reproducibility and consistency of the jet constitute the primary objectives in the development of this facility at the present time.

ANTICIPATED TECHNIQUE IMPROVEMENTS The following techniques will be attempted to increase the reproducibility of jet and damage characteristics: 1. Back leakage in the nozzles has been greatly reduced by the replacement of the original neoprene seals by lead seals (Figure 10). However, the tight-fitting lead seals involve substantial friction losses in the impact phenomena. Such a seal, which must be forced in with a hammer, is clearly a source of poor reproducibility. It is anticipated that these will be replaced by close-fitting, machined, aluminum pistondiscs. The fit between the piston and the nozzle chamber walls would then be substantially reproducible between shots, though some increase in back leakage may occur. 2. The nozzles will be filled under water to eliminate the possibility of air pockets in the nozzles, which may have been a source of poor reproducibility. 3. The nozzle mounting block will be more firmly attached to the gun mount to eliminate variation in the impact point. The above modifications should allow more systematic results to be obtained, e.g. as reported by the Naval Ordnance Laboratory3 (Figure 11).

TECHNIQUE MODIFICATIONS PREVIOUSLY EXAMINED 1. A layer of "Scotch Tape" was applied to the nozzle orifice to act as a "burst diaphragm" to see whether the resultant initial pressure build-up in the chamber would result in a cleaner, more repetitive jet. However, this modification did not have the desired effect. 2. A "Constant-Pressure" nozzle design, i.e. a nozzle with internal air chambers, the expansion of which should provide a more constant pressure on the water during its expulsion from the chamber, led to mechanical difficulties in that the gasket material flowed plastically into the air chambers. Also, no marked improvement in jet characteristics was noted. 3. The effect of varying the quantity of water in the nozzles was investigated. It was found that nozzles with less than the maximum possible quantity of water often led to somewhat higher jet velocities, but the repeatability in this condition was very poor. 4. In an attempt to get a spherical drop impacting the target rather than a jet, a spherical drop of about 1.8 mm was placed above the nozzle outlet and expelled by striking with a teflon piston driven by the gas gun pellet. This resulted in a jet with a spherical shell configuration of relatively large diameter (about 12.5 mm for a nozzle diameter of 1.8 mm) and travelled at a very low velocity of 150 m/s. The photographs show a curious, small particle travelling with the jet in each case, which appeared to be a piece detached from the teflon piston (Figure 12). Thus, this technique did not produce a high velocity spherical drop as had been hoped. -4

DETAILED JET CHARACTERISTICS The pictures taken of each firing were classified according to the principal jet configuration. Four main jet shapes were observed. Each jet photographed was then identified as one of the given types or a combination of two. Previous researchers with similar equipment have indicated a strong dependence of jet shape on the nozzle loading technique, with the shape of the meniscus at 4 the nozzle opening being a controlling factor. The present results suggest that the jet shape is also dependent on the pressure with which the water is expelled from the nozzle. This is brought out by the correlation of jet shape with gun pressure. The four main jet configurations are illustrated below: A. C. D. Typical photographs of these major types are illustrated in Figures 13 through 16. Figure 17, showing type B, also indicates on closer inspection that the large head is primarily spray with a solid liquid jet proceeding up to the base of the small Monroe jet. -5

The correlation of these arbitrary jet configurations with gun pressure is shown in Figure 18. With nozzles 4 (D=1.0 mm) and 5 (D=1.8 mm), the jet shape seemed to become more cylindrical, i.e. narrow with a strong central jet, as pressure increased. Nozzle 6 (D=3.1 mm) seemed to teach this condition at lower pressures and then the jet diverged as the pressure increased. The relative damaging power of the different jet configurations has not yet been determined. -6

BIBLIOGRAPHY 1. Hammitt, F. G., "Laboratory Scale Devices for Rain Erosion Simulation," Report No. IP-775, Department of Nuclear Engineering, The University of Michigan, April 1967. 2. Pitek, M. T., "Preliminary Water-Jet Impact Studies Using a Gas Gun-Momentum Exchange Facility," Report No. 08153-2-T, Department of Nuclear Engineering, The University of Michigan, January 1967. 3. Scher, M. P., "Liquid Impact Simulator," Report NOLTR 65-181, U.S. Naval Ordnance Laboratory, White Oak, Maryland, June 1966. 4. Dowden, F. P., and J. H. Bronton, "The Deformation of Solids by Liquid Impact at Supersonic Speeds," Proceedings of the Royal Society, 263, 433-450 (1961). -7

-825 20 A A NOZZLE 4 (1.0 mm dia.) 0 NOZZLE 5 (1.8mmdio.) 0 5 o 1100-0 0. ALUMINUM 0 i5* i _ l 2517 0 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 1 - Pit depth vs. gun pressure for 1100-0 aluminum.

-910 9 8 A NOZZLE 4 (1.0mm dia.) o NOZZLE 5 (1.8 mm dia.) o x 7 o A w IL a w o A I — 00 i 2 ALUMINUM 350 400 450 500 GUN PRESSURE (Ibf/ln2) Fig. 2 - Pit depth/diameter vs. gun pressure for 1100-0 aluminum

-10540 520 500 480 I~~-^ ^^~~~~~~~~o 460 I440,.l 420 400 2519 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 3 - Pellet velocity vs. gun pressure.

-1117 16 0o'o 15 | 13 — 0 II z_ 10 ~~~~~~~~~~~~I0 ~220 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 4 - Pellet momentum vs. gun pressure.

-1213.0 12.0 a.. cc _11,o -. -J a.9.0 8.0 7.0 u IJ__ I___E__l\ — lI I2521 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 5 - Pellet energy vs. gun pressure.

-132 NOZZLE 4 (1.0 mm dia.) 2900 z NOZZLE 5 (I.8mmdio.) o NOZZLE 6 (3.1 mm dia.) 2500 2100 A I o 0 A a I 0 A I 1700 B 00 Io GA0 A A o w A 0A 1300 AG I-. 0 900 o 500 T'LE~~~~~~~ I I I I " L252 I 300 350 400 450 500 GUN PRESSURE (Ibf/in ) Fig. 6 - Jet velocity vs. gun pressure.

-140 NOZZLE 4 (1.0 mm dia.) & NOZZLE 5 (1.8 mm dia.) 120 E NOZZLE 6 (3.1 mm dio.) 100 -80 80 2E'U) 60S R 40_ o 0 l~& 0 0 20L L11 2252I3 300 350 400 450 500 GUN PRESSURE (Ibt/in2) Fig. 7 - Jet mass vs. gun pressure.

-1530 261 NOZZLE 4 (.Ommdio.) A NOZZLE 5 (1.8mmdia.) 0 NOZZLE 6 (3.1 mm dia.) 22 18 0 14 z 3 I-| 10 A 0 A 6O 0 Q 0 0.2 0 1500 190 1 0 2524 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 8 - Jet energy vs. gun pressure.

-168.0 7.0 0 0 NOZZLE 4 (1.0 mm dia.) A NOZZLE 5 (1.8 mm dia.) o NOZZLE 6 (3.1 mm dio.) 6.0 3 0 —ft 0 a x 5.0 0 E _ B _ 0 z w 3.01 o 0 s. A:0 a0 2.0 1 ~ 00~ ~ ~~0 1.0 A30- 350 40 0 I450 500 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 9 - Jet momentum vs. gun pressure

1 7 _v_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... |~~~~~~~~~~~~~~.......... | | Z l.:::> B::S:'>.::.:sS::::B::':S::-:S -V::..:::... a. ss...... -.....h ~ i}a:..'g.':'....................... BBB BB-'BB'&B'B - "-' —"''' "'". -..'' S "' "'"""S.'.-.S....,'.::<V'::-:S::':'''"''; o';;'";';;.";;;;;;;';;;'-;';;;;;;;.";;;'';';;;';;;';;;;';";'';';;..'';;;;;"-';'.;"'"';;;'.;';''.'' r:;..........:-;:: - -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.............. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..................v. -. -.......................... —......................................................................iTiERSET........................ _........................ 00 f:000 f f 0 0... f00 0 ^;000 0 0 00 0 f; W$000........................................... _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......................................... _;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......................:: _; ) ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~............................ -........ -- _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..........................0 0 0 0 _i......E............................... E__........................................... - _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....00...; 0.a............................................SS................................................................................ _11|10 ff _0_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... S:00 0 W;0:; _ __~~~~~~~~~~~~~~~~~~~~~................................. 0000 Xi- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... *:: gEE iEE EEEEEREEE~gEEEE~lEE0000000000000:0000000000000:::0;i:000000:0:..............::..................:..::.:............ X -::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::......:....:............................... - E~~~~g;;;;;; 000000000000000000000000000000 0 0;;::: _ f f::t 0:::::: S~~~~~~~~~~~......................: iEE is iV: 0:::;::E::::: - 0:0:: E E;E iS i...........................g~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..........................::i~:E::i_::::00000~ ~ ~ ~ ~~ ~~.............. _:; 2<26: 1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~................................................... Fis+ 10 Cowarxson of back leakege (above3~~~~~~~~~~~~~~~~~................ in ear~~~~~~~~~~~~er rurs with 1ater tests (be1Ow)~~~~~~~~~~~~~~................................ in ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.................t w e re u s d

-18~~~I-.~ GUN PRESSURE w w ~> ~~~~z w dI o -- a- w u a. GUN PRESSURE GUN PRESSURE l d n r 3 W m W ^ ~PELLET ENERGY z~ W - d I- d p 2527 GUN PRESSURE GUN PRESSURE Fig. 11 - Expected dynamic properties of pellets and jets. (Ref. 3)

-19-............................................ -- --------- --- --......................-...................................................-........................................................................................................................................................................................... - - -........................................................................................................................................................................................,..................................................................................................................................................................................................-.............................................................-.................................................................................................................................................................................................-.............................................................................................................................................................-.................................................................................................................................................................................................................... - -..............................................................-................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... ---........................................................................ --..................................-................................-......................................................................................................................................................................................................-.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... -................................................................................................................................................................................................................................................................................................................................... --..................................................................... - - - -.......... - - - -................... -........................................................ I............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................-............................................................................................................................................-......................................................................... - -.......... - - -.......................I.............I.....................................-........................................................................................................................................................... -......................................I.......................... --................................................I....................................................................................................................................................................................................................... - -................... - - -...........................................................................................................................................I....................I................................................................................................................................................................................................... - - - - -.............................................I...............................................................................................................................................................................................................................................................I........... -im.....................................................................................................-................................................................................................................................................................................................................................................................................................................................................-.............................................................................................................................................................................................................................................................................................................................................-..........................................................................................................................................................................................................-.................................................................................................................................................................................................................. I — 11I 11 -................................................................................-....................................................................................................................................................................................................................................-.......................................................................................................................................................................................................................................................................................................................................... - - -...............................................................................................................................................................................................................................................................................................................-...........................................................................................................................................................................................................................................................................................................................................................................................................................-....................................-..........................................................................................................................................................................................................................................................................................................................-.......................................................................................................................................................................................................................................................................................................................................................................................-...............................-.........................-...............................................-.........................................................................................................................................-..................................................................................................................................-..........-..............I.................. - -...........................................................................................................................-................- - - - -...............................................-....................... - -................................................................................... I —..............................................................................................................................................................................................I -....................... -....................................................................................................................................................................................................................................................................I..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................-....................................................................................................................................................................................................................................................................................................................-.................................................................................................-....................... 11..................-...................................................................................................................................-................................................................................................................................................................................................................................................................................................................................................................................... - - - -...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................I................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... - -.............................................................................................................................................................................................-..........................-...............................................................,x,:;,:X,-:-.............................................................................................. ----------------------- Fig. spherical shell type jet t Sec*

Fig. 13 - Photograph of type A jet configuration. Set is traveling at 1820 ft/sec.

Fig 14 - Photograph of type B jet configuration. Jet is traveling at 1560 ft/sec.

-22Fig. 15 - Photograph of type C jet configuration. Jet is traveling at 1560 ft/sec.

— 23Fig. e 16 Photograph of tCypecT D~~ jet cosnfigurat ioun. Jet is traveling at 1560 ft/sec.

~~~~~~~~~~~~~~~~~~~~~~~ u~~~~~~~ * tic. 17 - Hligh Speed Photograph of Type B Jet from Nozzle 5 (1.8 m).

-25I ~~,.r —----— NOZZLE 6 0 | ZL (3.1 mm dia.) C B 0 ~NOZZLE 5 ^ ((1.8mm di.) C) J NOZZLE 4 t) 0-^-^11^(I.0 mm dia.) WC w I2533 300 350 400 450 500 GUN PRESSURE (Ibf/in2) Fig. 18 - Approximate jet configuration vs. gun pressure.