NASA NACA-WR-L-23-1946 Variation with Mach number of static and total pressures through various screens《穿过不同屏幕的静态和总压力的马赫数变化》.pdf

1、U.S. DEPARTMENT OF COMMERCENational Technical Information ServiceNACA WRL 23VARIATION WITH MACH NUMBER OF STATIC AND TOTALPRESSURES THROUGH VARIOUS SCREENSNATIONAL ADVISORY COMMITTEE FOR AERONAUTICSWASHINGTON, DCFEB 1946fProvided by IHSNot for ResaleNo reproduction or networking permitted without li

2、cense from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-b,_= _._, _.NATIONAL ADVISORY COMMITTEE FO-R AERONAUTICSTI RTIMI, REP()RTORIGINALLY ISSUEDFebruary 1946 asConfidential Bulletin L_F28VARIATION WITH MACH NUMBER OF STATIC AND TOTALPRES

3、SIIRES THRO_H VARIOUS SCREENSBy Alfred A. AdlerLangley Memorial Aeronautical LaboratoryLangley Field, Va.REPRODUCED BYU.S. DEPARTMENT OF COMMERCENATIONAL TECHNICALINFORMATION SERVICESPRINGFIELD, VA 22161N1! ,iWASHINGTONNACA WARTL_E REPORTS are reprints of papers originally issued to provide rapid di

4、stribution ofadvance research results to a_nauthorized group requiring them for the war effort. They were pre-viously held under a security status but are now unclassified. Some of these reports were not tech-nlcally edited. All have bee_roduced without 9b._%D_ein order to expedite _enera/ dlstribut

5、i0/L_ _: ! INFORMATION SERVICE L_ii_ . _ _ U.S. DEPARTMENTOFCOMMERCE _ “SPRIHGFiELD,VA.22161Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4“_ _ - o :o

6、 o ooo o _ ,NATIONAL ADVISORY COMMITTEE FOR AERONAUTICSV_RIATION WITH MACH ._A_!BER OF STATIC AND TOTALPRESST/RES THROUGH VARIOUS SCREENSBy Alfred A. AdlerS U_iARYTests were conducted in the Langley 24-inch high-speed tunnel to ascertain the static-pressure and total-pressure losses through screens

7、ranging in mesh from3 to 12 wires per inch and in wire diameter from 0.023to 0.041 inch. Data were obtained from a Mach numberof approximately 0.20 up to the maximum (choking) Machnumber obtsinable for each screen.The results of this investigation indicate thatthe pressure losses increase with incre

8、asing Mach numberuntil the choking Mach number, which can be computed, isreached. Since choking imposes a restriction on themass rate of flow and maximum losses are incurred atthis condition, great care must be taken in selectingthe screen mesh and wire dimmeter for an installationso that the chokin

9、g Mach number is not approached atthe maximum operating velocity.INTRODUCTIONIn the design of ducts for aircraft it has becomenecessary to know the losses in static and total pressurethrough screens installed within these ducts. Data onthe losses through screens at low speeds have long beenavailable

10、, but for current aircraft ducting problemsdata on the losses through screens at high speeds arenecessary. Tests were thereforeconducted in theLangley 2_-inch high-speed tunnel to ascertain thestatic-pressure and total-pressure losses t_roughscreens ranging in mesh from _ to 12 wires per inch andin

11、wire diameter from 0.023 to 0.0_l inch, at Machnumbers from approximately 0.20 to the maximum (choking)Mach number obtainable for each screen.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2MMchokeAHqcdmdSPluIu2:“: oo oo SYMBOLSO $ O0 _ :0 , NACA CB

12、 No. L5F28Mach number ahsad of screenchoking Mach number, also known as limitingMach number, the Mach number ahead ofscreen at which a Mach number of 1 isobtained completely across openings inscreentotal-pressure loss through screenstatic-pressure drop through screendynamic pressure ahead of screens

13、ection drag coefficient _Drsg/Unit are_ . qmesh, wires per inchwire diameter, inchscreen solidity, ratio of blocked area tooriginal free area _2md - m2d 2)density ahead of screenvelocity ahead of screenvelocity downstresm from screenAPPARATUS AND ._TKODSThe Langley 24-inch high-speed tunnel, in whic

14、hthese tests were run, is a nonreturn, induction-typetunnel with the induction nozzle placed downstream fromthe test section (reference 1). The total pressurethroughout the test section is therefore equal to atmos-pheric pressure, except for a negligible loss through theentrance screens.Each screen

15、was supported for tests within a16-inch length of seamless steel tubing having an inside1 inches (fig. 1), which was mounteddiameter of 53Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-“ .!“ i.:W .NASA CB N : 3longitudinally in the test section of t

16、he tunnel by means1of _ inch-diameter steel cables.The Mach number was determined from the staticpressure ahead of the screen, which was measured by meansof two diametrically opposed static-pressure orificeslocated in the walls of the supporting tube 3 inches_uead of the screen. The static pressure

17、behind thescreen was measured by means of two additional static-pressure orifices located at a distance of 4 inchesbehind the screen. The total-pressure loss through thescreen was taken as the difference between atmosphericpressure and the total pressure as indicated by twotubes placed behind the sc

18、reen with the noses in theseine plane as the static-pressure orifices. The tube-entrance losses were assumed to be negligible.RESULTS AND DISCUSSIONThe data for all the screens tested are presentedin figures 2 and 3, which show the static-pressure dropand total-pressure loss, respectively, plotted a

19、gainstNach number. The data show, mainly, that both static-pressure drop and total-pressure loss, in percent ofdynamic pressure, increase with increasing Nach n_:_beruntil the highest obtainable test Nach number is reached.This Nach number is known to correspond to the chokedcondition, since further

20、 increase in tunnel speed didnot increase the Mach number ahead of the screen.The data of figures 2 and 3, plotted in terms ofscreen solidity rather than mesh and wire dimneter, arepresented in figures 4 and 5. From these figures itcan be seen that the pressure losses are dependent onlyon screen sol

21、idity and Msch number within the range ofthis investigation.Figure 6 shows dra_ coefficient cd plotted againstMach number. These values of drag coefficient wereobtained from the equationAp PlU! (u2- Ul)cd - _ .q qProvided by IHSNot for ResaleNo reproduction or networking permitted without license fr

22、om IHS-,-,-This equation was d_Ived on the asstumption that con-ditions were uniform across the wake. As was expected,the data show that the drag coefficient increases withincrease in Mach nurabe_,Since choking of tha i_iow through a tube occurswhen a Mach number of 1 is reached at the cross section

23、of minimum area, choking of the flow would be expectedto occur when a Mach number of 1 is obtained completelyacross the openings in the screen. This choking fixesa limit to the Mach number that can be obtained in theflow ahead of the screen. Thero al_e now two possi-bilities. If the total pressure a

24、head of the screen ismaintained constant, no further increase in mass rate offlow is possible. Any decreases in back pressure willonly increase the losses through the screen. If, how-ever, the total pressure _ead of the screen isincreased - as is possible in flight - the mass rate offlow can be incr

25、eased. This increase in mass rate offlow will be accompanied bF large losses _ud will pro-gress at a far lesser rate than for speeds belowchoking. It is highly desirable therefore that care betaken in the selection of screen mesh and wire diameterso that the choking Mach number is not approached att

26、he maximum operating velocity. The following equation,derived from the continuity eqaation, the adiabatic law,and Bernoulll,s equation for compressible flow, relatesthe speed at which this choking occurs to the screenvsriables :1 - 2md + m2d2 =0.579MchokeC1 + 0.2Mchoke2) 3This relation, presented gr

27、aphically in figure 7 interms of the screen variables and in figu, e 8 in termsof screen solidity, shows good agreement with theexperimentally determined choking Mach numbers.C0NCL_Di NG RENARKSTests in the Langley2_-Inch high-speed tunnel toascertain the ststlc- and total-pressure losses throughscr

28、eens indicate that the losses increase with increasingProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ili!i:illiiliii_._ii:.:.i!:.NACA CB No. L5F28 5Nach number until the choking Math number, which can becomouted, is reached. Because choking imposes

29、s restrictionon the mass rate of flow and because maximum lossesare incurred at this condition, great care must be takenin selecting the screen mesh and wire diameter for aninstallation so that the choking _Zach number is notapproached at the maximu_m operating velocity.Langley Memorial Aeronautical

30、 LaboratoryNational Advisory Co_._mittee for AeronauticsLangley Field, Va.REFERENCEStack, John, Lindsey, W. F., and Littell, Robert E.:The Compressibility Burble and the Effect of Com-pressibility on Pressures and Forces Acting on anAirfoil. NACA Rep. No. 646, 1938.Provided by IHSNot for ResaleNo re

31、production or networking permitted without license from IHS-,-,-eoooooo_-:o_ ae8o6m_oe_ aeooooo goooooo:.:-.ooooo_:o:-:oooProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-:. . : !.L_.8 “NACA CB No. : i : “: :.- .-oo ,oo ooFig. 1cONFIDKNTIAL-S/o,/c-pre

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33、saleNo reproduction or networking permitted without license from IHS-,-,-.ACACB.0.ii_ii_:_:i:!:i:“:_:“!_:.;.“!: Fig. 2c,dI32I032IC _.)O.O,1_/“ / I.o_sPe“C) ,_ = 7._ J003SJ023ol/./oI0 ./A-/8,ure 2.IA.Z./_l, Tch(d)m = _.3 .4- .5n_m_er 7 l_lNATIONAl. ADVISORYCOMMITTEE FOI AERONAUTICS- Continued.Provide

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