1、NASA Technical Memorandum 4549Effect of Passive Venting on Static PressureDistributions in Cavities at Subsonic andTransonic SpeedsRobert L. Stallings, Jr.Lockheed Engineering however, only thestatic pressure results will be presented in this report.The tests were conducted at Mach numbersfrom 0.20
2、to 0.95. The shallow cavities tested hadlengths of 42.00 in. and 32.16 in. and a depth 2.40 in.The deep cavities tested had a length of 32.16 in.and a depth of 4.80 in. Cavity width was held con-stant at 9.60 in. Based on boundary layer measure-ments from reference 4 for similar configurations andte
3、st conditions, it is assumed the boundary layerapproaching the cavity was turbulent and had athickness of approximately 0.50 in.A complete set of tabulate d pressure data is pre-sented both in hard copy and on a floppy disk at theback cover of this report.SymbolsaF, aRApvheight of lip vent openings
4、of forwardand rear lip vents respectively, in.(see fig. 4(b)internal cross-sectional area of pipevents, in 2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-CpCPxxxFPLhlMoc, MachPplpoopt,ocqooRoopressure coefficient, p-pc_qocpressure coefficients for
5、orificenumber xxx (see tables III X)p/fluctuating pressure level, 20 log q-_cavity depth (not including ventchamber depth), in.Lt length of cavity floor covered withtape, in. (see table I)cavity length, in.free-stream Mach numbermeasured surface static pressure, psifluctuating pressure, psifree-stre
6、am static pressure, psifree-stream total pressure, psifree-stream dynamic pressure, psifree-stream unit Reynolds number,ft-1Tt,oo free-stream total temperature, FU velocity, ft/secUoc free-stream velocity, ft/secw cavity width, in.x distance in streamwise directionrelative to cavity leading edge, in
7、.(see figs. 2-5)y distance in spanwise direction relativeto cavity centerline, in. (see figs. 2-5)z distance normal to flat plate relativeto plate surface, in. (see figs. 2-5)5 boundary-layer thickness(U/Uoc = 0.99), in.Experimental MethodsModelsBecause of the large number of models and config-urati
8、ons investigated, the tests were conducted dur-ing two phases (identified as phase 1 tests and phase 2tests) with each phase requiring a separate tunnelentry. For these two phases of testing, the cavitymodels were installed in different flat plate assem-blies. The external geometries of the two flat
9、 plateassemblies were the. same except for the region of thetrailing-edge wedge downstream of the cavity and forthe fairing aft of the cavity on the lower plate surface.It is assumed that these differences had no significanteffect on the cavity flow field.The cavity/plate assemblies were located app
10、rox-imately on the centerline of the wind tunnel test sec-tion. A photograph of a typical model installationis shown in figure 1. Vertical loads on the flat platewere carried by six legs attached to the tunnel floorstructure, and lateral loads were carried by four ca-bles attached to the tunnel side
11、wall. The forward andmiddle pairs of legs were swept forward to improvethe longitudinal cross-sectional area distribution ofthe plate assembly for blockage considerations. Fair-ings were mounted around the cavity on the lowerside of the flat plate.Sketches showing dimensions of the three basiccavity
12、/plate assemblies used in the tests are pre-sented in figures 2, 3, and 4. These assemblies weredesigned to accommodate the porous floor configura-tions (phase 2 tests, fig. 2), the pipe vent configura-tions (phase i tests, fig. 3), and the lip vent configura-tions (phase 2 tests, fig. 4). For all a
13、ssemblies, the flatplate length, width, and thickness were 111.00 in.,48.00 in., and 1.00 in., respectively. The leading-edgecross section of the flat plate was a 12:1 ellipse. Thecavity width for all models was 9.60 in. For all cavitymodels, the origin of the coordinate system used todefine the pre
14、ssure instrumentation location was onthe flat plate surface longitudinal centerline at thecavity leading edge (see figs. 2(a), 3(a), and 4(a).The cavity leading edges for the porous plate andpipe vent models were 36.00 in. downstream of theplate leading edge, and the cavity leading edge for thelip v
15、ent models was 39.00 in. downstream of the plateleading edge. This increase in distance from the plateleading edge for the lip vent configurations shouldresult in less than a 2 percent change in boundary-layer thickness at the cavity leading edge based onestimates from equations 27.21 and 27.66a of
16、ref-erence 6. A turbulent boundary layer on the platesurface ahead of the cavity for all three cavity/plateassemblies was obtained by installing a 0.10-in-widestrip of no. 60 grit 1.00 in. downstream from the plateleading edge. The size and location of the grit wasdetermined from references 7 and 8.
17、 Boundary-layerprofiles measured during the tests of reference 4 withthe same flat plate and similar cavity configurationsas the phase 1 tests confirmed that the boundarylayer was turbulent at the cavity entrance.The cavity/plate assembly used for the porousfloor configurations contained a 2.40-in-d
18、eep cavitywith a porous floor, as shown in figure 2(a). Beneaththe porous floor was a 1.00-in-deep vent chamberthat when combined with the porous floor, permittedProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-flowfromthe high-pressureregionsof the c
19、avitytothe low-pressureregions. Cavity lengthsof 42.00and 32.16in. wereobtainedby testingwith andwithout a filler blockinstalledin the rearsectionofthe cavity.Detailsof theporousfloorassemblyareshownin figure2(b).Theporousfloorhadaporosity/ _ Hole areas )of 11.2 percent To_ _-_o_-_a 100 , which is t
20、hesame porosity as the pressure cavity model of refer-ence 1. This porosity was obtained by a matrix of ap-proximately 6000 holes of 0.098-in. diameter locatedas shown in figure 2(b). The extent of the floor areathat was porous was varied by covering the full widthof the floor with tape in patterns
21、that were symmet-rical about the lateral centerline (50-percent length)of the cavity (see fig. 2(c). For the 42.00-in-longcavity, tests were conducted with 100, 75, 50, 25, 8,and 0 percent of the floor area having porosity and forthe 32.16-in. cavity, tests were conducted with 100,75, 50, 25, 10, an
22、d 0 percent of the cavity floor areahaving porosity. The porous, floor was made up ofsix individual plates (see fig. 2(b) that could be re-moved to create additional passive venting configu-rations. Plates 1 and 3 or 1 and 6 could be removedto form transverse-slot passive venting configurations(whic
23、h will be referred to as slot vent configurations,fig. 2(d) consisting of a 1.41-in. slot at each end ofeither the 32.16- or 42.00-in-long cavity, respectively.These slot vent tests were conducted with and with-out the porous floor covered with tape. Plates 4and 5 were necessary to adapt the vent ch
24、amber foruse with the lip vent configurations to be discussedsubsequently.The major differences in the cavity assembly forthe pipe vent configurations (phase i tests) shown infigure 3(a) and the cavity assembly for the porousplate configurations (phase 2 tests) are that thecavity floor for the pipe
25、vent configurations was solidand the cavity aft wall could be positioned at anycavity length. For the present tests, the cavity lengthwas fixed at 32.16 in. or 42.00 in. As with the porousfloor configurations, cavity depth was held constantat 2.40 in.The cavity/plate assembly used for the pipe ventc
26、onfiguration (phase 1 tests) was originally designedand fabricated to accommodate a wide range of cav-ity lengths. The sliding plate that provided this capa-bility extended past the flat plate trailing-edge wedgeas shown in figure 3(a). This extension resulted ina difference in the plate geometry in
27、 this region ascompared with the plate used in the phase 2 tests.Also, as previously mentioned, the geometry of thecavity aft fairing on the lower surface of the flat platewas not the same as the fairing used for the phase 2tests. It is assumed that these differences in the plategeometry had no sign
28、ificant effect on the cavity flowfield. More detail on this cavity/plate assembly canbe found in reference 4.Details of the pipe vent configurations are shownin figure 3(b). Although the pipes occupy volumein the cavity, it is anticipated that in a practicalapplication they could be arranged between
29、 stores,launchers, etc., to minimize the effects of this reduc-tion in volume. The pipe vent models were fabricatedby bonding steel wall pipes of various diameters,lengths, and pipe arrangements to a 0.030-in-thicksteel plate. The pipe-plate assembly was then at-tached to the top of the cavity floor
30、 with flatheadscrews. Because of problems with localized failuresof the bond between the pipe and the steel plate,retainer brackets for the pipes were necessary to en-sure that the pipes did not separate from the plate.One of these brackets was installed at each end ofthe pipes, as shown in figure 3
31、(b). For each cav-ity length, four pipe vent configurations providingventing areas (based on the pipe inside diameters)ranging from 0.88 in 2 to 2.32 in 2 were tested. Thepipes were arranged symmetrically about the cavitycenterline and were located such that the pressure in-strumentation at y = 0.00
32、 in. and y = 2.40 in. wasexposed to the flow.Shown in figure 4 are sketches of the lip ventmodel assemblies. The cavity/plate assembly usedfor the lip vent configurations is essentially the sameassembly used for the porous plate tests. The ma-jor differences are that the cavity depth for the lipvent
33、 models is 4.80 in. and the location of the cavityleading edge, which is the origin for the instrumen-tation coordinate system, is 39.00 in. downstream ofthe plate leading edge. Cavity length for the lip ventmodels was constant at 32.16 in. In order to providea vent chamber between the forward vent
34、and the aftvent, the porous floor assembly shown in figure 2 wasused for these configurations. Tests were conductedwith and _ithout the porous floor covered with tapeto provide solid floor and porous floor comparisons.A retaining bracket (see fig. 4) was required for therear lip vent assembly to pre
35、vent it from lifting offthe cavity floor.Details of various components of the lip ventmodels are shown in figure 4(b). Four lower lip blocksfor each lip vent assembly were fabricated to providea lip vent opening range from 0.00 in. to 0.50 in.Since the lip vent assemblies contained sidewalls thatwer
36、e 0.25 in. thick, the width of the lip vent openingswas 9.10 in.A summary of descriptive information for allconfigurations tested is given in table I.3Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,i _Wind Tunnel and Test ConditionsThe tests were c
37、onducted in the NASA Lang-ley 8-Foot Transonic Pressure Tunnel. This facil-ity is a continuous-flow, transonic wind tunnel capa-ble of operating over a Mach number range from 0.2to 1.3. The tunnel can obtain Reynolds numbersfrom 0.5 x 106 to 6 x 106 ft -1 and stagnation pres-sures from 3.7 to 29.5 p
38、sia. A description of the fa-cility is given in reference 5.Tests were conducted with the fiat piate surfaceat an angle of attack of 0 relative to the test sectioncenterline for the nominal test conditions shown inthe following table. Values of boundary-layer thick-ness presented in this table are f
39、rom reference 4 andwere measured at a location of 36.00 in. from theplate leading edge. These measurements were ob-tained with the same fiat plate used in the phase 1tests of the present investigation.Configuration1-4, 7, 85, 61-6161-61-61-6Pt,oo, Tt,oo,Moo lb/in 2 F0.20 23.61 100.20 25.00 100.40 22
40、.22 100.60 20.83 100.80 14.18 100.90 12.47 100.95 11.81 100Roo, 5, qoo,ft -1 in. lb/in 22.0 106 0.45 0.652.2 .45 .683.6 .48 2.234.7 .47 4.123.8 .50 4.173.5 .52 4.183.3 .55 4.17Instrumentation and MeasurementsStatic pressure orifices with an inner diameterof 0.020 in. were located on the surfaces of
41、theflat plate and the cavities. Based on data fromreferences 4 and 9, lateral pressure gradients on thecavity floor were small, and therefore for the presenttests, a single longitudinal row of pressure orificeson the cavity centerline was considered adequate fordefining the type of cavity flow field
42、. For the porousfloor models and the lip vent models, static pressureorifices were also located on the floor of the ventchamber. Detailed information on the locations ofall the orifices is given in table II and figure 5.Surface pressure measurements on the flat plate,cavities, and vent chambers were
43、 obtained by us-ing electronically scanned pressure (ESP) transduc-ers referenced to tunnel static pressure. These trans-ducers had a range of 5 psid and a quoted accuracyof 0.01 psi. This increment in pressure correspondsto the following increments in pressure coefficients:Moo ACp0.20.40.60.80.90.9
44、50.016.004.002.002.002.003As discussed in reference 4, local Mach numberson the flat plate surface (h = 0.00 in.) in the regionof the cavity installation could vary by as muchas 0.03 from the nominal free-stream values shownin the table above; however, because of the relativeinsensitivity of the cav
45、ity pressure distributions to aMach number variation of this magnitude at subsonicand transonic speeds, nominal free-stream valueswere used for reducing all data.Tunnel free-stream static and stagnation pres-sures were measured with sonar-sensed mercurymanometers having an accuracy of 0.0035 psi.For
46、 the shallow cavity configurations (configura-tions 1-6), the pressure measurements are the av-erage values of 10 data samples taken over a periodof i sec. An indication of the repeatability of data forthe shallow cavity configurations with this averagingprocess is shown in figure 6, where data are
47、presentedfor three repeat data points. Although the maximumdifference in the level of the pressure distributions issomewhat greater than the transducer accuracy, thedifference was not considered large enough to justifyadditional averaging.The lip vent configurations (configurations 7and 8) are deep
48、cavities and, as shown in reference 9,can have unsteady flow fields that cause large pres-sure fluctuations inside the cavities at subsonic andtransonic speeds. An indication of the data repeata-bility for these configurations with 10-data-sampleaveraging as used for the shallow cavities is shownin
49、figure 7 for 2 sets of 3 repeat data points. Bothsets of data are for the same model at the same testconditions. These data show that the cavity flowunsteadiness results in large variations in the pres-sure levels over the rear portion of the cavity floor.Also shown in figure 7 are average pressure distribu-tions obtained by averaging the pressures from thethree repeat data points. A comparison of the aver-age pressure distribution for each set of data is shownin figure 8. These re
