1、U.S. DEPARTMENT OF COMMERCENational Technical Information ServiceNACA TM 798FLOW PHENOMENA ON PLATES AND AIRFOILS OFSHORT SPANNATIONAL ADVISORY COMMITTEE FOR AERNAUTICSWASHINGTON, DCJULY 36Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by I
2、HSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NOTICETHIS DOCUMENT HAS BEEN REPRODUCEDFROM THE BEST COPY FURNISHED US BYTHE SPONSORING AGENCY. ALTHOUGH ITIS RECOGNIZED THATARE ILLEGIBLE, IT IS BEINGIN THE INTEREST OF MAKINGAS MUCH INFORMATIONCERTAIN PORTIONSRELE
3、ASEDAVAILABLEAS POSSIBLE.Provided 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-,-,-NATI0_AL ADVISORY COMMITTEE FOR AERONAUTICSTECHNICAL NEMORANDUM NO. 798FLOW PHE
4、NON_ENA ON PLATES AND AIRFOILS OF SHORT SPANBy H. WinterSUMMARYInvestigations on the flow phenomena at plates andcsmbcred models were carried out with the aid of forcemeasurements, some pressure distribution measurements,an_ photographic observation. The experimental methodsarc described and the res
5、ults givon. Section III of thiswork gives a comprehensive account of the results and en-ables us to see how nearly the lift llne and llft surfacetheories agree with the experimental results.ITTRODU CT I0NThe flow phenomena about plates and airfoils of _hortspan are still not well known although such
6、 bodies are ap-plied for airplane tall surfaces, ships rudders, etc.In what follows will be given a description of a completeseries of tests on such bodies, the results of which maybe applied for all practical needs.I. OBJECT OF INVESTIATIONThouF_h the flow phenomena about plates and profilesof larg
7、e span have received a good deal of attention,those about small span plates and airfoils have not yetbeen satisfactorily investigated and moat of the data wepossess were obtained on apparatus that is already out-dated. There is, nevertheloss, _ large field of applica-tion for bodies of large aspect
8、ratio Y/b2, where F isIf *“Stromungsvorgange an Platten und profilierten K_rpernbei kleinen Spannweiten.“ VDI - Special Issue (Avia-tion), 1936. Extract from Thesis. Complete work ob-tainable at the Institut fur Hydro- und Aerodynamlkof “t_e Technical High School, Danzig _M_,CE0e,NATIONAL TECHNICALI
9、NFORMATION SERVICEU.S DEPARIMENI OF COMMERCESPIIINGF ELD. YA. 22161Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 N.A.C,A. Technical Memorandum No. V98the projected area and b the span of the body. as, forexample, ship rudders and airplane tail su
10、rfaces where itis desirable to have as large a transverse force as possi-ble with favorable drag relations. Furthermore, the phe-nomena of flow separation and pressure equalization at thesides which play so prominent a part in these short-spanbodies are of general significance for numerous other flo
11、wproblems.Since a theoretical treatment of these flow phenomenastill meets with insurmountable mathematical difficulties,it is the object of this paper to extend and complete thetests carried out so far, so as to obtain results that maybe applied for all practical purposes.The characteristics of the
12、 flow are largely determinedby the angle of attack and the shape of the plate or air-foil. As far as shape is concerned, there are essentially _three determining factors: form of outl_ne, profile sec-tion, and amount of warping. To determine the effect ofthese on the forces and flow pattern, is one
13、of the mainobjects of this work which, however, will be confined tounwarped bodies. The tests were carried out under thestimulus and leadership of G. Fl_gel, at the wind tunnelof the Technical High School at Danzig. In addition toour own measurements and observations, there were alsoevaluated the te
14、st data obtained by other coworkers in thesame field at the Flow Institute. A short report on someof this work will be found in reference 1.II. TESTSI. Sha;_es and dimensions of Investigated models.-The models investigated fall into two groups: thin flatplates and cambered, mostly symmetrical models
15、. Their de-termining characteristics are given in tables I and II.(See p. 31,325 The tunnel velocity was always in the direc-tion of the plane of symmetry.The following plan forms were used for the flat plates:rectangular, elliptical, semielliptlcal, and triangular(the last two were used for two dif
16、ferent wind directions).The plates were entirely of 3.5 mm (0.138 in.) sheet brass,the upper surface being well ground. To reduce as far aspossible the effect of finite thickness at least for thelarger angles of attack, the plates were made sharp at omeedge on the suction side (fig. 2).Provided by I
17、HSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N.A.C.A. Technical _emorandum No. 798 SThe effect of the symmetrical camber was investigatedonly for the rectangular shape, the profile form beingkept the same while the aspect ratio was uniformly in-creased. For th
18、e aspect ratio F/b 2 = I/1.0 a thicke._profile was obtained by increasing the height of the Gottin-gen profile 409. The thickness at all points was increasedproportionately, so that for this case as well as for F/b 2= I/1.14, the effect of the thickness ratio c_uld be madeout at least on two unequal
19、 Joukowski profiles, s All mod-els of this first set had flat side edges.In another set of tests the same models (except theJouhowsS_i profiles) were measured with rounded slde edges.With models R.P.la, R.P.2a, R.P.5a. and R.P.Ta the round-ing began at a distance from the side edge equal to 80 per-c
20、ent of tile largest profile thickness, with R.P.6a at 100percent. Figure 1 shows the amount of rounding whichturned out to be most effective for model R.P.Sa. Nonsym-metrical camber was investigated only for a circular out-line (model E.P.1)._. Method of conducting test.- With few exceptionsthe tunn
21、el tests were made at a jet velocity of about 28meters per second (63.2 miles per hour). The ReynoldsNumbers (referred to the maximum chords of the models)were between the values Re = 0.3 l0 s and Re = 1.V l0 s. As several control _ests showed, the forces andtherefore the flow pattern about flat pla
22、tes are practi-cally independent of the l_eynolds Number even for smallvalues, thus making possible the application of the testresults to larger models. Cambered models, however, mayshow the effects of the characteristics.The pressure measurements at the plate surface weretaken with a sounding devic
23、e that consisted essentially ofa shall brass tube of 1.0 mm (0.04 in.) outer diameterwhich transmitted the static pressure to a Fuesz alcoholmanometer. The forward end of the tube was closed by asemicircular stopper, and at S.5 mm from the end of thetube was provided with a 0.4 mm (0.16 in.)boring f
24、or tak-ing up the pressure. It is necessary to set the apparatusas far as possible parallel to the stream-line direction.At larger angles of attack it is rather d_fficult, on ac-count of the strong turbulence, to set the plate edgesparallel to the average stream direction.*Joukowsl_i profiles are ob
25、tained, as is well known, by con-formal transformations.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 i_.A.C.A. Technical Hemorandum No. 798The flow-plcture studies were made partly by means ofobservations on streamers. On the suction side this m
26、eth-od is applicable only at small angles of attack; at largerangles the threads roll up on account of the strong eddies.In this case smoke tests were found to be of a_vantage.For producing the smoke, ammonia and concentrated hydro-chloric acid in combination with compressed air were used.To render
27、the flow at the boundary layer visible, themethod of Fales (reference 2) was applied to advantage.The upper surface of the plate was spread over with a mix-ture of soot and petroleum. When the flow is sot up thepetroleum evaporates and the soot follows the stream lines.This method was found to be ve
28、ry useful and failed onlywhere the flow velocity was very smallo3. Force _easurements.- The polars, moment coeffi-cients, and normal force coefficients (the latter only forrectangular plates) are arranged in groups for each shape.In computing the air-force coefficients and the angles ofattack, the e
29、ffect of finite Jet diameter was correctedfor using the method of Prandtl-Glauert (reference 3).The corrections were for the most part below 1 percent.The r_oment coefficients were referred to the maximum chordof the model.A. Flat Plates:a_ Rectangular p_lates (figs. 2, 3, and 4) (refer-ence 4). -Th
30、e pola-rs-Cfig_-2-_-show for equal values oflift coefficient ca , an increase in the drag coefficientcw with decreasing span, as may be expected from the air-foil theory of Prandtl. Correspondingly, in figure 3, atequal anglo of attack a, there is a decrease in the nor-mal-force coefficient cn with
31、increasing aspect ratio F/h ,2.Within the range of small angles of attack a. theincrease in llft with span for a = 0 is to be ascribedto the beveled edge on the suction side, which acts as anunsymmetrical camber on the plate. If we consider, to afirst approximation, the plate to be replaced by its c
32、en-ter llne, we have a sharp-edge broken profile whose camberratio for equal area, plate thickness and beveling In-creases with increasing span. In the ideal case of infi-nitely thin, flat plates for any shape of outline, the cncurves (fig. 3) all start at the origin and with increas-Provided by IHS
33、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-N.A.C.A. Technical _emorandum No. 799 5ing angle of attack, gradually go over into the measuredcurves; the profile effect of the beveling is only evidentat relatively small angles of attack.A characteristic feature of
34、 the curves of normal-forcecoefficient is that for small values of F/b _ they ap-proach linearity and with increasing values curve more andmore. This fact indicates a transition range of the flowwhich at one end of the range approaches the simple two-dilnensional flow (F/b 2) = 0 and at the other en
35、d ap-proaches a limit at which, with F/b _ = _, the forces evi-dently follow the sin 2 variation (reference 5) with an-gle of attack.A peculiar behavior is shown at the plate with F/b 2 =1/0.66 in the range of angle of attack between 450 and 490 .In this case we find an isolated branch of the polar
36、curveleading to very large alr forces and lying in the projec-tion of the normal polar curve. The tangential force co-efficients, depending not only on the viscosity coeffi-cient but also on the very small difference in pressurebetween the front and rear edges, were not computed. Theirabsolute value
37、s are small compared to the normal coeffi-cients, except near a = 0, so that the force was practi-cally normal to the plane of the plate._ Elli_t!c 1_lates (figs 5 and 6).- Im the lowerrange up to a lift coefficient of about 0.9 the polar aswell as the normal-force curves are very similar to thecorr
38、esponding curves for the rectangular plate. If thelift-line theory is still assumed to hold _rue also forthese spans and for small angles of attack, then theoret-ically the drag coefficient for the elliptic plate, forexample, at F/b m = 1/2.0would be, at the most, about 2percent smaller than for the
39、 rectangular plate. The bev-eling on the suction side makes the plate have a largercamber ratio at the rim. This further causes the liftdistributions for elliptic and rectangular plan forms toapproach each other. The polars, too, show almost com-plete agreement in the lower range.While there was a s
40、teady increase in th_ maximum liftwith decreasing span up to F/b 2 = 1/0.66 for the rectan-gular shape, there was a marked unsteadiness in the case ofthe elliptic form. At F/b 2 = 1/_.0 and F/b 2 = 1/1.8,the maximum-lift coefficient is about 0.95 and suddenlyincreases at F/b 2 = 1/1,82 to 1.42. The
41、models withFib = 1/1.27 (circular plate), Ill.o,and llO.Slap-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 N.A._.A. Technical MemGrmndum No. 798preach, above the angle of attack of 20a, mean polar andnormal-force curve which almost agrees with th
42、e curve forthe square plate. At F/b 2 = 1/0.81 there is a similarunsteadiness, as in the case of the rectangular plate withF/b = 1/0.66.c) Semlelli_.p_tlc and_trlan_ula_r_lates (figs 7 to13).- For equal span more favorable results are almost al-ways obtained with the straight edge used as trailinged
43、ge. _ot only is the drag lower at equal lift but in mostcases there is also a larger maximum value for the llft.It aFpears moreover that with the ellipse or broken edgeof the triangle used as leading edges, the same forces areobtained at smaller angles of attack than with the straightsides as leadin
44、g edges.On a physical basis the reason for these deviationsin the aerodynamic effect may be explained as follows: Ifboth of these forms are replaced by their llft lines (thatis, the lines Joining the centers of pressure of the pro-file sections), which should be assumed at about t/4 fromthe leading
45、edge, the curves of figure ll are obtained.It then appears that the more important middle portion oflift line 2 is more removed from the effect of the trail-ing vortex sheet, so that in this case there arise smallerdownward velocities. Form 2 therefore in comparison withl. leads to greater effective
46、 angles of attack at equalgeometric angle of attack and hence the agreement with theobserved effect.B. Cambered Models (figs. 14 to 20).Symmetric models _rith G_ttlngen profile 409 (thicknessratio 12.6 percent) and with rectangular plan form weretested_ using aspect ratios F/bm = 1/2.0, I/1.5, 1/1.0
47、,and 1/0.5 (figs. 14 to 1V). The side edges of the modelwere first provided with a plane bounding surface parallelto the mid plane. In the lower reglon up to a llft coeffi-cient of about 0.50, the polars were similar to those of theflat plates. For equal aspect ratio the polars in eachcase almost co
48、incide. In the upper range the cambered air-foils showed themselves to be considerably less favorable.Between a = 14.50 and 22.5 , depending on the aspectratio, there is a critical angle above which all polarsshow a strong increase in drag. At F/b 2 = 1/2.0 and 1/1.5flow separation sets in, whereas at F/b m 1/1.0 and 1/0.5the flow essentially adheres to the model in spite of In-creased separation. The maximum llft for all airfoils wasProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N.A.C.A. Technical Memorandum No. 798 7considerably less than
