1、Copy 1 RML51B13 NACA RESEARCH MEMORANDUM TEE EFFECT OF END PLATES, END STRUTS, AND DEPTH OFSUBMERGENCE ON THE CHARACTERISTICSCF C ISYFROFOIL By Kermeth L. Wadlin, Rudolph E. Fontana,and Charles L. Shuford, Jr. Langley Aeronautical Labo4atoryLangley Field, Va.! CLSSIFCPTO CANGED To - ON$ c C Tills do
2、cument contains classified :rf:-r:1. - - Uonsi etensu Of foe U:rod fateS Wit!uL f:r toof the Espionage Act. USC - in-ian or tnt r“Vei5iCt of Ito contentS in soy manner to an unauthorized person is ao r - !nfcrrr:atirn so clsi:rd may be iris no- - S-Li is the military and naval services of the TT!,-d
3、 a: rojriate z:11,officers an - t:eede ml Government who have a legitimate mu-n -st herruo, and! i:nl :uteo oiffveee - nd discretion who - I neresrmty moot he informed co ni-of. NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON April 121 1951Provided by IHSNot for ResaleNo reproduction or netwo
4、rking permitted without license from IHS-,-,-NACA RM L51B13NATIONAL ADVISORY COMMITTEE FOR AERONAUTICSRESEARCH MEMORANDUM THE EFFECT OF END PLATES, END STRUTS, AND DEPTH OFSUBMERGENCE ON THE CHARACTERISTICS OF A HYDROFOIL By Kenneth L. Wadlin, Rudolph E. Fontana,and Charles L. Shuford, Jr. SUMMARY A
5、n investigation was made in Langley tank no. 2 of the effect of end plates and end-mounted struts on the lift-drag ratios of a hydrofoil. The hydrofoil had an aspect ratio of 14 The tests were made at various depths below the water surface at speeds from 15 to 35 feet per second corresponding to Rey
6、nolds numbers fronf 0.873 x 106 to 2.04 X 106. These speeds were all above the limiting speed of wave-propagation (13.9 fps) for the 6-foot water depth used and below the range at which cavitation occurs. Only small improvements were found in the maximum lift-drag ratios by the addition of end plate
7、s and these improvements occurred only at low lift coefficients with small end plates. As the lift coefficient was increased above the value for maximum lift-drag ratio the optimum end-plate size increased; however, the absolute value of lift-drag ratio decreased. The detrimental effect of. the drag
8、 of the additional strut for a hydrofoil using end struts in contrast to a single central strut was greater than any beneficial effects due to the end-plate effect of the end struts. The ratio of the effective aspect ratio to the geometric aspect ratio varied with end-plate size approximately as pre
9、dicted by aerodynamic theory (Von Karmn and Burgers). Although the hydrodynamic data obtained with the end plates were slightly higher than the theoreti-cal curve, the agreement was good when the accuracy to which such data could be. obtained is considered. An approximate theoretical solution of the
10、 effect of depth on the lift of a hydrofoil was developed. The agreement of the experimental results with the results given by this solution was good.-p aProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACA EM L51B13 INTRODUCTION The use of end pla
11、tes as a means of increasing the effective aspect ratio of airfoils and thereby increasing lift-drag ratios has been inves-tigated at various times. In general, these investigations have not led to the use of end plates on airplane wings. End plates have been used on tail surfaces where the necessit
12、y for having two surfaces at right angles to each other enables the end plates to serve two functions. Because hydrofoils normally will be supported by one or more struts extending through the water surface, it is possible to use the struts for a dual purpose by placing them at the ends of the hydro
13、foil where they also serve as end plates. This possibility, together with other con-siderations, such as structural and stability considerations might result in the desirability of using end plates on hydrofoils has led to the present investigation of the effect of end plates and end struts on the l
14、ift and drag characteristics of a hydrofoil. Another problem considered in the present investigation is that of determining the effect of depth of submergence below the water surface on the characteristics of a hydrofoil. There is a great amount of aero-dynamic data available for use in hydrofoil pr
15、oblems but, in general, these data are for a fluid without boundaries, whereas hydrofoils may operate close to the boundary formed by the water surface. In order to extend the usefulness of these existing data, an approximate theoretical solution for the effect of depth of submergence on the lift of
16、 a hydrofoil is developed. Experimental data obtained with a hydrofoil of aspect ratio Ii- at various depths of submersion at speeds from 15 to 35 feet per second (Reynolds numbers from 0.873 x 106 to 2.04 x 106) and at angles of attack from _350 to Lo, with and without end plates and end struts, ar
17、e pre-sented. The investigation was conducted at speeds above the limiting speed of wave propagation (13.9 fps) for the 6-foot water depth of Langley tank no. 2. These experimental data are correlated with existing theory giving the effect of end plates on effective aspect ratio and with the develop
18、ed theory giving the effect of depth of submergence on lift. The .method for obtaining a theoretical solution of the effect of depth on lift was suggested by Mr. Thomas A. Toll of the Langley Stability Research Division.SYMBOLS L lift, pounds D drag, poundsProvided by IHSNot for ResaleNo reproductio
19、n or networking permitted without license from IHS-,-,- - NACA EM L51B13 3 CL lift coefficient (L/qS) CD drag coefficient (D/qS) CD1 induced drag coefficient cd section drag coefficient 0 S area of hydrofoil, square feet q free-stream dynamic pressure, pounds per square foot (v) V velocity, feet per
20、 second - P mass density, slugs per cubic foot C l section lift coefficient at finite depth of hydrofoil submersion C l section lift coefficient at infinite depth of hydrofoil osubmersion a angle of attack, degrees CL - finite lift-curve slope at finite depth of hydrofoil a submersion C l section li
21、ft-curve slope at finite depth of hydrofoil CL submergence C l section-lift-curve slope at infinite depth of hydrofoil a0submersion L/D lift-drag ratio (L/D)max maximum lift-drag ratioCL(L/D)max lift coefficient for maximum lift-drag ratio r circulation strength of vortex downwash at three-quarter-c
22、hord point due to hydrofoil vortex, feet per second downwash at three-quarter-chord point due to hydrofoil vortex image, feet per second Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_r NACA RN h depth of hydrofoil submersion below free water surfa
23、ce, feet C chord of hydrofoil, feet b span of hydrofoil, feet h area of one end plate, excluding hydrofoil section area, divided by chord of hydrofoil R geometric aspect ratio (b2/S) aspect-ratio correction factor for rectangular wings Re effective aspect ratio Ee effective edge-velocity correction
24、factor for lift DESCRIPTION OF MODEL Various end plates and end-mounted struts were attached to an 8-inch-chord hydrofoil having an aspect ratio of 4. Photographs of all the configurations tested are shown in figure 1. The hydrofoil, struts, and end plates were made of stainless steel. They were pol
25、ished to a smooth finish consistent with current wind-tunnel practice. The sections for the hydrofoil and end struts were the same as those used in reference 1. The hydrofoil had an NACA 641A412 section which differs from the NACA 641-J+12 section Only by elimination of the trailing-edge cusp; the s
26、ection characteristics of these two are essen- tially the same (see reference 2). The struts had an NACA 66 012 sec-tion. Figure 2 gives the ordinates for the hydrofoil and strut sections as computed from references 2 and 3. The five end plates tested consisted of 1 -inch-thick flat plates with elli
27、ptical edges. Three of the end plates were designed to cover various amounts of the two-dimensional pressure field about the hydrofoil computed at an angle of attack of 00, which was expected to be close to the angle for maximum lift-drag ratio. The coverage was such that the static pressure at the
28、boundaries of the end plates would deviate approxi-mately 20, 10, and 5 percent from the free-stream static pressure. The details of these end plates are given in figure 3. The pressure fields were computed by the method used in reference 11 and are shown by the dashed lines In figure 3.Provided by
29、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RM L51B13 - 5 The other end plates were rectangular and the details of these end plat-Z are given in figure 4. APPARATUS AND PROCEDURE The tests were made by using the main carriage of Langley tank no. 2. A st
30、ing support was used to reduce interference effects. Figure 5 shows a view of the test setup with the hydrofoil, supporting sting, and balance attached to the support structure on the carriage. The details of the supporting-sting arrangement are shown in fig-ure 6. The sting was supported by an 8-in
31、ch-chord strut having an NACA 661-012 section. The spacing between the strut and the hydrofoil was such. (i.5 chords) that the influence of the strut on the-flow at the hydrofoil should be negligible (reference 5). The hydrofoiiwas moved vertically by means of a motor-driven jacking screw which move
32、d the balance and hydrofoil as a unit. Change in angle of attack was obtained at the plate attaching the strut to the balance. Measurements of lift and drag were made by means of electrical strain gages. The force measurements were made at constant speed, angle of attack, and depth of submersion. Th
33、e depth of submersion is defined as the distance from the water surface to the point of the hydrofoil nearest the water surface. A range of submersions from 0.5 chord (I in.) to 11 chords (32 in.), of speeds from 15 to 35 feet per second, and of angles of attack from _3.50 to 400 was covered. Submer
34、sions where the end. plates protruded through the water surface were omitted. The maximum angle of attack was limited. to 4.00 since the maximum lift-drag ratios were expected to occur below this angle of attack. The change in angle of attack due to structural deflection caused by the lift and drag
35、forces on the hydrofoil was obtained during the calibration of the balance and the test data were adjusted accordingly. The supporting sting and strut were run alone at the same range of speeds, depths, and angles as when the hydrofoil was installed. For these tests the end of the sting was fitted w
36、ith a faired. cap. The tares thus obtained were deducted from the test data to give the net forces. The net forces were converted to the usual aerodynamic lift and drag coefficients by using a measured value of p of 1.966 slugs per cubic foot corresponding to a water temperature during the tests of
37、700 F. All coefficients were based on the area of the hydrofoil, 1.78 square feet. ORMN W_ 0-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 NACA RM L51B13 The correction for the ground effect of the bottom of the tank determined by the method desc
38、ribed in reference 6 was only 0.7 percent of the induced drag at the maximum depth of submersion (4 chords) and 0.1 percent at the minimum depth (0.5 chord). The correction to the angle of attack was even less. The corrections therefore were considered negligible.RESULTS AND DISCUSSION The results o
39、f the tests are presented in figures 7 to 13. In these figures lift and drag are plotted against angle of attack with speed and depth as the parameters. The fairings appearing in these figures were made by using cross fairings against speed and depth so the data are faired as a whole and not for ind
40、ividual speeds or depths. This same method of fairing was carried out in all subsequent figures. The data, converted to coefficients, are presented in figures 14 to 20 in the usual form for aerodynamic data. The present tests were made principally to investigate the effect of end plates, end struts,
41、 and depth of submergence on hydrofoil charac-teristics. The scope of the investigation was not sufficient to evaluate completely the effects of Froude number, Reynolds npmber, cavitation, and the possible effects of limiting speed of wave propagation in the towing tank. Care, therefore, must be tak
42、en in making specific applications of the results. - Lift coefficient did not vary with speed but the drag coefficient decreased with increasing speed. The variation of drag coefficient with speed was, however, very small at the higher speeds. The slopes of the lift curves increased with increasing
43、depth, but at depths greater than 2 chords the increase in slope was very small. Lift-Drag Ratio The variation of lift-drag ratio with lift coefficient for the hydrofoil with and without end plates is shown in figure 21 for a depth of 4 chords and a speed of 35 feet per second. It can be seen that t
44、he smallest end plate gave the highest maximum lift-drag ratio. Further increases in the size of the end plate reduced the maximum lift-drag ratio and increased the lift coefficient at which it occurred. Only a small increase in lift-drag ratio can be obtained in the region of maxi-mum lift-drag rat
45、io and this increase can only be obtained with small end plates. However, at high lift coefficients even the larger end plates improve the lift-drag ratio, though at lower absolute values thanProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA BM L5
46、1B13 7 at the lower lift coefficients. As the lift cQefficient is increased above the value for maximum lift-drag ratio the optimum end-plate size increases. Figure 22 shows the variation with depth and speed of the maximum lift-drag ratios and the lift coefficients at which they occur. With-out end
47、 plates the variation with depth was negligible at depths greater than 1.5 chords. As the size of the end plate was increased the effect of depth persisted to greater depths. As the speed was increased the maximum lift-drag ratio increased and the lift coefficient at which it occurred decreased; the
48、se effects of speed decreased with increasing speed. The effect of speed on the lift coefficient for maximum lift-drag ratio vaied with end-plate size. With no end plates the varia-tion with speed appeared to be negligible but it increased with end-plate size. The variation of lift-drag ratio with l
49、ift coefficient for the hydrofoil with the end struts is shown in figure 23. These curves are for several depths and a speed of 35 feet per second. As the depth is increased the maximum lift-drag ratio decreased and the lift coefficient at which it occurred increased. Apparently the strut drag impaired the lift-drag ratio to a greater extent than the end-plate effect
