NAcA t'?! "^ KB No. L5C30 t NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLy ISSUED April 19^4-5 as Eestricted Bulletin L5C30 EETECTS OF COMPRESSIBILITY AND LAROE AHGOS OEF YAW ON PEESSUEE INDICATED BY A TOTAL -PRESSURE TDBE By Milton D. Humphreys Langley Memorial Aeronautical Laboratory ^ Langley Field, Ta. WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the wair effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. DOCUMENTS DEPARTMENT L - 77 Digitized by tine Internet Arcliive in 2011 with funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/effectsofcompresOOIa MCA P.r No. L5C50 NATIONAL ADVISORY C^OIITTEE RIR AZRONaUTICS p^c "pp 7'''""X'^T) ■^^^f" "'"."■^T'TTJ EPP^C^S '^^^ CC'^'PRliSSIBlLITY AND LARG'E; ANGLES OF YlJi 0^' FT^SSTJaS INDIO.^^ED 3'' A TOTAL-PKES iURE VBE By !.I ! 1 1 G n D . H^r.-nph r e y s SmsiARY The effects cf 3ornrr3SsIbility and angle of yaw on the oressure measured by a rovnd-nose and a flat-nose tctal-presaure tube "'jave b~en lave stiga bed . The Lests were conducted in tl.3 LangleT rectangular high-speed tiuinel at ?.Iuch nurrbera fro.a G.5 to O.Q for anglea of yaw from 0° to 180°. '^he results indicated that no error was incurred in the measureinent of total prossi-.re b7.^ elbh.er cube for angles of yaw from 0° to 10° in ti.e Mach number range investigated. At constant "ach numbers, the round-nose tube had a linear variation of botal-nressure error with angle of yaw at angles ranging frora 50° to 70°. This characteristic is desirable in yaw heads of the Y-type. The flat-nose tube had a nonlinear variation of total-pressure error with angle of yaw in this range, HITRODUCTION Available inf orTiation on the pressure measured by total-pressure tubes yav;ed v;lth ^esnect to the air stream was Llraited to small angles of yaw and low Mach numbers. An investigation has therefore been conducted to deter- mine the nressLire rneasured by a total-pressure tube for Mach nujnbers ^from 0.5 to O.9 over the angle-of-yaw range from 0° to 180°. Two types of total-pressure tube were tested, a roi:nd nose and a flat nose. The information obtained in this report should facilitate analysis of flow-direction measursi.-ients and other aerodynamic properties . MCA RB ITo. L^CJO APPA??ATUS ANE METHODS '.[t.e tests were made in the Langley rectangular hle-h-SDeed tunnel, which is an induction- tyt)e tunnel having s 4- "by lo-inch test section. At'^osr'heric air is in-'^uced to flov; through the tiinnel by an iaouction nozzle located downstream fro:m the test section. Gxceot for a STiall loss of presr3ure resulting from the passage of air through the screens at the tunnel entrance, the total nressure at the test section is a'^'proxi'Dately equal to atmosoheric pressure. This vi'ind tunnel is basically similar to the ]I.A.C..'\. high-sneed v^ind tunnel described in refei-ence 1. 'The round-nose and the flat-nose total -pressure tubes used in this investigation were luade of brass tubing having an outside diar.eter of O.125 inch and walls O.O25I1- inch thiol. The tubes wore constructed in the form of an L with a head 1 inch long at an angle of 90° to the supporting SDJndle (fig. 1). The total-pressure tube was niouiited in the center of the test section -.vith the supporting spindle normal to the tunnel wall and passing out through a hole of ariproximatelv — inch diameter drilled in the wall. The "8 head o "^ the tube cculrl be rotated about the spindle axis through the angle-of-yaw r^nge and could be locked in any desired position. S WJBOLS H total pressure measured above absolute zero ■.'vith air at rest H' r^ressure indicated by total-nresrure tube M f re 3 - 3 1 re air; Kach number Mj^ I'.lach number at nose of tube computed on assiimp- tionsthat flow is adiabatic and that II' equals static pressure at nose of tube n„ free-stream static rirecsure NAG A R3 Ko. L^CJO q free-stream dynamic pressure p density, slugs i^er cubic foot V velocity of mean free stream, feet ner second \{/ angle of yaw of instrument head PRECISION It is believed that oractically all the errors to v^hich the quantities measured in this investigation are subject are of an accidental nature. The variation in Mach number in the test section Darallel and normal to the tunnel axis is insignificant for these tests. Tunnel constriction effects should be negligible because of the small size of the total-pressure tube relative to the tunnel size. Air-flow misallnement and the error 1° in alinement of the total-nressiire tube are within tp • 4 The free-stream static pressure and the error in total -pressure as indicated by the total-pressure tubes v^ere measured by visual observation of liquid-filled manometers. Liquids of different densities were used in the manom.eters for various ranges of pressure dif- ferences to insure large rises of the liquid and thereby minimize the errors in readings. An indication oi the magnitude of the accidental error involved in these data is given in figures 2(a) and 2(b), each of which shows the scatter for two tests with the total-pressTire tube at an angle of yaw of 65°. Check points are indi- cated by flagged symbols. The data presented have been correct^'d for the total-pressure loss resulting from the nass^ge of the air throug?! the screens at the tunnel entrance. The amoijnt of this loss v/as determined by measurements r:iade in the test section and in the low-SDeed region ahead of the entrance cone and v/as checked by computa- tions of the pressure loss through screens. RSSLTLTS MI) DISCUSSION The variation of total-pressure error, in terms of total pressure, with Mach number for the round -nose and h MCA RB Ho. L505O for the flat-nose tubes is shown in figures 2(a) and 2(b), respectively. At constant angles of yaw of 20° or greater, the total-nressure error increased v/ith increasing Mach number. The rate of change of the error with Mach nixnber increased as the angle of yaw was increased from 20° to approximately 90°, where the rate of change of the error was at a raaxlmiajn. At angles of yaw from 90° to l30°, the slopes decreased with increasing angle of yaw . 'l\ie variation in u,he total-pressure error ;'Vith Fach n-oraber became increasingly irregular in the free-stream Mach number range from 0.7 to 0.3 for angles of jav-i between 110° and 150° (figs. 2(a) and 2(b)). If the flow is assumed to be adlabatic axid the pressure measured h{ the tube H' is assumed to correspond to the static pressure of the flow in the vicinity of the opening in the nose of the tiibe for these conditions, the local Mach n'oraber M^ Ccin be computed. The value K - Po 1 for a Mach niimber of 1.0 'would be 0.i|.72. H It can be seen that the irregularities In the curves E - F' , occur near a value of of 0.[j_72 and are -Dossibly due to the formation or movement of shock. The variation of total-pressure error, in terras of free-stream d;^/namlc pressure, v;lth Mach num.ber is shown in figure 3« 'For angles of yaw greater than 20°, the total-pressure error had a small, nonlinear variation with Mach number. This variation becam.e irregular at the higher angles of yaw and the most pronoLtnced direc- tional changes occurred near 90°. Ilo error was Incurred in the measurement of total pressure by either the round- nose or the flat-nose tube over the Mach niOTber range extending from O.J to O.9 f'or an angle -of- yaw range from 0° to 10° (figs. 2 and 3). The variation of the total-nressure error, in terms of total nvessure , with angle of yaw is presented in figure I4. for several Mach numbers. The curves were obtained by cross-plotting the data -oresented in fig- ure 2. The results show that the total-pressure error Increased with nicreasing the angle of yaw from 20° to approximately 87° and then decreased as the angle of yaw vifas increased to l30°. At an angle of ya\. ^^ , ,.- . at the nose of each total-pressure tiibe was approximately At an angle of yaw of loO°, the pressure measured NAG A R3 ITo. L5G30 5 tho same for equal Fach numbers and was 'below free- stresjTi static pressure p^ at all -spesds. The relation given by H J ■"or either tube at an inclination of l80° to the air IT P, stream is correct Vi/lthin t2 loorcent of — • " ° over H the Fach number range investigated. This agreement presents a possible method of determining static pres- sure hj means of a simple instru:!ent that may be useful in some installations. The variation in the total-r-ressure error, in terms of the stream dynamic nrcssure, as a function of angle of yaw for constant Mach numbers is shown in figure 5> a cross plot of the data in figure 3. Whereas the flat- nose tube had a nonlinear variation of total-pressure error with angle of yaw ovei' an angular range from 50'^ to 'JO'~'toc constant Kach nuribers, the r-ound-nose tube had a linear change - an indication that the round-nose tube would be desirable for use in yaw heads of the Y-tyoe. A Y-type yaw head using round-nose tubes at an included angle of 120*^ should give a linear variation in calibration factor over an angular range of tlO°. In order to give an indication of possible effect of ccmnressibility on the calibration factor of a ya'w head, the slopes of tho curves of figure 5(^) ^-^® shown in figure 6 for angles of yaw between '30° and 70°. This curve indicates a small effect of compressibility on the calibration of a yaw head having ro'jnd-nose tubes if the yaw head support is assurr.ed to have negligible influ ?nce . ;0'jclti3icn: Tests made to determine the effects of compressibility ana angle of yaw on the pressure measured by a ro'and- nose and a flat-nose total-pressure tube indicated that: 1. Total-pressure tubes of the type tested in this investigation would give true total pressure for angles of yaw of 0° to 10° for Fach numbers" from 0.3 to 0.9. FACA RB llo. L5C50 2. At constant Mach nuj^bers, the ncund-noss tuloe had a linear variation of total -pressure error ;vi th angle of yav/ at angles ranging from 50° to 7^°. The fl. at-ncse tube had a nonlinear variation of the total- nres^Mre error with angle of ya.v in this range. The roun.l-nose tithes set at an included angls of 120° should there "^ore be desirable for use as co-n-oonents of a Y-type yaw head. This yaw head should give a linoai' variation in calibration factor over an angular range of ±10*^. Langle- I.Ie'norial Aeronautical Laboratory national Advisory Co^miittee for Aeronautic: Langloy Field, Va. " REPERENGS 1. Stack, John: The ^T.A.C.A. High-3oeed ;Vind Tunnel and Tests of Six Proneller Sections. NAGA Ren. Ko. I4.65, 1953. NACA RB No. L5C30 Fig. 1 Spindle Bra s s tubing a/^Stia 'ODZS^ "wet // -^t\ Head, of tube ^ J Enla r^ed yieiv of pose (a) Round nose. Spindle / Brass tubing aiZ5''O.D.''Q.0B54-" wall — ' Head, ~<^ of \r tube^ T J En I aroed view of nose ^h) rinf nn^e national advisory [OJ r lai no3e. committee fop aeronautics, /^/oure I .— To td /—pressure tubes. Fig. 2a NACA RB No. L5C30 H 'JOJJd 9jnS99JCl-IO40± NACA RB No. L5C30 Fig. 2b "C3 1 -rj^ 'jojjd 9jnss&jd-ioioj_ Fig. 3a NACA RB No. L5C30 ,H-H ^ "^ QQ ^ ' JOMa djn'sss>jcl-io4qj_ NACA RB No. L5C30 Fig. 3b 5: <^ . L Q) -Q F ^ 3 c < •0 ^^ Q) c/^ O ~rj k Q^ ^) ■Tl H^ .■^ Cl g: ^ § 1 \ O k , M M Fig. 4a NACA RB No. L5C30 ^ 00 IN «' o '^ n Si H Z lu OH n s J / 1 / / / / / / / / / / f 1 / / / / / / / / / \ / ^ / A / > / / ^" y ^ ( / / / / ( / / y 1 / r A / / V \ r r ( \ \ ^-^ ^ \ \ S \ \ \ \ ""^^ ^^^ ^ \ \ \, \ ^ \ ^ A / / ^**i^ ^^ \ 4\ \ 1 II ^ ^ ^ °0 N ^o lO n f\2 § ^ ? o fv V o 3 w O to < ^ o ^§ ' jojjd djnzsdjdi-\oio± NACA RB No. L5C30 Fig. 4b ^s OD Cv ^ ^ ^ to NATIONAL ADVISORY COMMITTEE F0« AERONAUTICS. 1 1 1 1 1 i / / 1 j , / / / ' / i / \ 1 / i \ / / / 1 / / / / / / / / / / / ^ -^ r-' / V / / y / /■ / ^ / / / i ^ L ______ ^ c -^ C V -^ - ^ \, \ \> v!^ N^ ^\ / x^"^ . \ N^ ^\ \ / / ■^v^ ^ ^ A -^ ^ II ^ < ^ 00 t~- ^ lO ^ M ^J 00 2 <^ QQ O 2^ ^ ^ o o I .H'H 'jojja ajns9aJcl-io^qj_ Fig. 5a NACA RB No. L5C30 wj 1 1 SORY )NAUTIC / ' y L ADVI OR AERC ll / 1 331111 VNOIIV 1: a -I / 1 \ 1 1 1 1 K 1 M ^ 3 / ' / ^ / w V (^ L— i— 7 r^ Vv V \ -00 v^ <\ ^ =^ ^ ^ 1 =^ ^ "^^ % V X \ \ \ ^ cv o '^^ o ^•0 0(J V)^ s^ Q VO ^ ■^ ^> ■-< (0 ^ ^1 ^^ ^ ''^ O ^ ^^ ^ O Js^ ^^^ V fi?^ o Q go^ ^ o ' ?^ ^ 5Q) • "J:^ Q).$:3 o ^ 8^^ "^ . ^ Sj;"^ ^> @^5 ^S o i^ .H-H NACA RB No. L5C30 Fig. 5b 1 '-' -\ 1 ; >- 1- n a. = 1 Si 1 / / ^|i n ' / ^2 ft ' / Z .Ai 1 / j t / j 1 o 1 1 1 \ 1 ' / . \ J 1 / / <^- ^0 X / y/^ V y^ /'. / \ I 1<0_ v^ -^ ifc 1 ^ ^^^ "^ H % X V \ \ \ \ ^ ^ o ^ ^ ^ 00 o 5^ o ^ ^ ^ o ^ ^ ? ^ ^ ^ 3 xj ^ V o O ^ CD (0 1 <0 +^ c: ^ ^ 1 ^ lO % o o :3 ,H-H 'jojjQ djnssdjd- /cPiqi_ Fig. NACA RB No. L5C30 o V AL ADVISORY FOP AERONAUT NATION COMMITTEE 1 \ \ «5^ <=Q K to ^i \ § s § 8 Ci Q> o o • (D-Q :3 !b UNIVERSITY OF FLORIDA 3 1262 08105 009 7 UNIVERSITY OF FLORIDA -«^m DOCUMENTS DEPARTMENT ^ 1 20 IVIARSTON SCIENCE LIBRARY P.O. 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