1、,NATIONALADVISORYCOMMITTEEFOR AERONAUTICSTECHNICAL NOTE 4122EXTERNAL INTERFERENCE EFFECTS OF FLOW THROUGHSTATIC -PRESSURE 0RJ3?ICES OF AN NACA AIRSPEEDHEAD AT A MACH NUMBER OF 3By Norman S. SilsbyLangley Aeronautical LaboratoryLangley Field, Va.WashingtonOctober 1957.Provided by IHSNot for ResaleNo
2、reproduction or networking permitted without license from IHS-,-,-TECHLIBRARYKAFB, NMI!llll!lllllll;llllllNATIONALADVISORYCOMKTMEE FORAERONAUTICSMlbba7qTECHNICALNOTE4122EXTERNAL NCE EFFECTS OF FLOWTHROUGHSTATIC-PRESSURE“ORIFICESOF AN NACAAIRSPEEDHEAJ)ATAMAcHmERoF3By Noman S. SilsbysuMMARYWind-tunnel
3、 tests have been made to detemnine the static-pressureerror resulting from external interference effects of flow through thestatic- ressure orifices of an NACA airspeed head at a Mach number ofB3 and O angle of attack.The results indicated that the static-pressure error increasedalmost linearlywith
4、increase in mass flow through the orifices. At-, a mass-flow rate corresponding to that which would be obtained at highaltitudes for an airplane in a 45 climb and for which the airspeedinstallation incorporates an airspeed indicator, a Mach meter, and andaltimeter, the error in static pressure would
5、 be about 6 percent witha corresponding error in Mach number of 3 percent. h a vertical cldmbwith this airspeed system the error would be 8 percent in static pres-sure and 4 p=cent in Mach number. The static-pressure error of theforward set of orifices was not influenc by varying flow rates throught
6、he rear orifices. However, varying flow rates through the forward ori-fices caused a small effect of 1 percent or less on the static-pressureerror of the rear set of orifices.INTRODUCTIONAirsped installations on airplanes usually include a nmiber ofindicating instments or recording instruments or bo
7、th. Because of thevolume of these instruments and the connecting tubing, air flows intoor out of the airsped system in a dive or climb, respectively. Theflow through the tubing causes a pressure loss snd hence the instrumentsare subjected to a ressure that is different from the pressure at thestatic
8、- or total-pressure source. This pressure 10SS is, of course, theA well-known pressure lag. (See ref. 1.) The volume of the airspeed sys-tem may be a source of another error. This error is associated with theProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IH
9、S-,-,-2 NACA TN 4122interference of the flow through the static-pressureorifices on theexternal flow. If the interference is appreciable, the static pressurein the region of the orificesmay be ected to be different from thatwith no flow through the systan. For exsmple, at supersonic speeds flowout o
10、f the static-pressureorificesmay cause a shock wave and hence anincrease in the static pressure. Flow into the orificesmay cause anexpansionwave or a decrease in static pressure.Jh order to determine the magnitude of this interference effect,tests were made at a Mach number of 3 in the Langley g-by
11、g-inch highMach number jet on an NACA airspeed head at 0 angle of attack. Thisairspeed head has two separate sets of static-pressureorifices spacedaxially on the tube. Measurements of static pressure in the chsmber ofeach set of orifices were made with mass flow out of the orifices up toabout 4.2 X
12、10-6 slugs per second and into the orifices up to about.b”slug per second.0.6x 10 The measurements were made at two stagna-tion pressures in the tunnel for which the coesponding Rolds numbers(basedAh1PPC.Pc,oApRrTtv.on tube dismeter) were about 0.77 X 10 and 1.2 X 10.SYMBO.IStotal area of static-pre
13、ssureorif ces leading to each cham-ber of airsfie head, 1.25 X 10-i Sq ftaltitude, ftlength of mass-flow measuring tube, 3.72 ftpressure, lb/sq ftpressure in chsmber of airspeed head, lb/sq ftpressure in chamber of airspeed head with zero flow throughorifices, lb/sq ft pressure drop in mass-flow mea
14、suring tube, lb/sq ftgas constant for air, 53.3 ft/deginternal rtiius of mass-flow measuring tube, 3.22X 10-3 fttemperature, %time, secfree-stresm velocity, ft/seca%.bProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 41-22 38“Qv total volume of
15、 airplane airspeed installation,._lLCu ftw mass flow, this maximum mass flow is of the order ofthat which would flow through the orificesof this type of airspeed headconnected to the usual set of indicating instruments for the conditionof the airplane changing altitude at a rate-of 1, feet per secon
16、d at sea level. Tests were made for mass-flow both into and-outof the ori- “fices; for each test, the flow was always in the ssme direction for bothchsmbers. For flow out of the orifices, the mass-flow measuring tubewas opened to atmospheric pressure throug+ a valve with which the flowrate was conol
17、led (fig. 2). The msximum mass flow for this directitin .WaS 4.2x 10 slugs per second. For flow into the orifices, the mass-flow measuring tube was connect through the valve to a very low pres-sure tank; however, because of the low tunnel static pressure and hencethe relatively low pressure differen
18、tial for this flow direction, themaximum mass flow obtainablewas about 0.6 X 10-6 slug per second. TheReynolds number of the flow out of the orifices,based on the diameter v.of the larger orifice (0.052 h.), was 400 for the mass-flow rate of,4.2x 10-6 slugs.er second. *:Measurements were recorded by
19、 means of standard NACA differential-pressure cells. Data were obtained for differential pressures between:(1) tunnel static and chsmber static pressures, (2) chamber static pres-sure and pressure at the end of the mass-flow tube, and (3) the pressuredrop in the mass-flow tube (see fig. 2). Also rec
20、orded during the tests“weretunnel stagnation temperatures and pressures and the temperature ofthe air flowing through the mass-flow meas_ing tube. Schleiren picturesof the flow passing the airspeed head were_taken at right angles to t-he -direction of air flow into or out of the orifices of the airs
21、peed hem. ,Measurements were made for two tunnel stagnationpressures, 75 and115 lb/sq in., for which the correspondingReynolds numbers (basal. on. airspeed-head tube dismeter) were about 0.77 X 106 and 1.2 X 106,respectively.RESULTS AND DISCUSSIONThe static-pressureerror due to mass flow through the
22、 static-pressure orifices of the airspeed head was determined from measurementsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 4122 5.-,wof the static pressure in the airspesd-hesd chsmbers relative to thestaticpressure at a tunnel-wall orifi
23、ce about 1 foot upstream of theairspeed orifices (fig. 2). Because of the longitudinalpressure gra-dient in the tunnel, the measured pressure difference-for zero mass flowthrough the orifices was not zero for either the forward or rear set oforifices. Ih order to indicate only the external interfere
24、nce effectsof flow through the orifices, the measured static-prqssuredifference(as a fraction of the tunnel static pressure) as plotted against themass-flow parameter v was arbitrarily displaced to go throughp.v however,inasmuch as the shock waves were weak, photographs are not presented.The interpr
25、etationof the results of figure 3 for an airplaneclimbing or diving may be facilitatedby coverting the mass-flow para-Wmeter into related quantities involvtng flight conditions.Pwv -e;-&,-&),S7540 - )L - -=.T.:-._ . .- -. J6W 09icifkebmlikmKluhwwrfaa+o“”&1r 0 0043imh-&m#a m0 .052- imh-dmwkr wtlces-.
26、-Figure 1.- Airspeed head aspressure chamber. FiljotSions are in inchefj.Sedial Ofmltiutmmmlifiedby Insertionof an additional tube into each static-tubtig remved and pitot opening plugged. “All I_j.near mlI-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS
27、-,-,-Po/rORIF/CE/IM4SS-FLO W MEA.YJRING TUBE+ TO SW7CE W SIKTIONU* + OR PRESSURE.FECWDING PI?ESSVI?E CELLSFigure 2.- Sket&“showing mss -f low and pressure -meamrb,g t3etup for one chamberof airspeed head.v Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-
28、,-,-NACA TN 4122.09.07.Od.05.04.03PC- P=(J P-.01o-.01-.MFigure 3.-.4 -.2 0 2 .4 .?. .8 1-o u 1.4 1-0 1A xw(a) Forward orifice.Variation of static-pressureerror of airspeed head wiwmass-flow parameter at ch number 3.pmVmAthProvided by IHSNot for ResaleNo reproduction or networking permitted without l
29、icense from IHS-,-,-12 NACA TN 4122PC- PC()Pm.12.11.10.09.08.07.06.05.0.0s.02.010-.01-.02-.M-.114-.4 -.2 0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8X lU.P-:-A.2(b) Rear orifice.Figure 3.- Concluded.=1,-.,:.-GNACA - Langkg Field, Va.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
