CER83-84JEC-JAP-BB-NH29.CSU Project 2-95380.For Gabrial Electronics, Inc.Includes bibliographical references (page 7).December 1983

Bienkiewicz, Bogusz J.

Cermak, Jack E.

Hosoya, Noriaki

Peterka, Jon A.

English

Cermak, Jack E., author

Peterka, Jon A., author

Bienkiewicz, Bogusz J., author

Hosoya, Noriaki, author

Fluid Mechanics and Wind Engineering Program, Fluid Dynamics and Diffusion Laboratory, Department of Civil Engineering, Colorado State University, publisher

Mountain Scholar (Digital Collections of Colorado and Wyoming)

DRAG FORCE ON MICROWAVE ANTENNA by 1 J. E. Cermak2 J. A. Peterka 3 B. Bienkiewicz and 4 N. Hosoya DRAG FORCE ON MICROWAVE ANTENNA by 1 J. E. Cermak2 J. A. Peterka 3 B. Bienkiewicz and 4 N. Hosoya for Gabrial Electronics, Inc. P.O. Box 626 Scarborough, Maine 04074 Fluid Mechanical and Wind Engineering Program Fluid Dynamics and Diffusion Laboratory Department of Civil Engineering Colorado State University Fort Collins, CO 80523 CSU Project 2-95380 December 1983 1Professor-in-Charge, Fluid Mechanics and Wind Engineering Program 2A . P f ssoc1ate ro essor 3Assistant Professor 4Graduate Research Assistant CER83-84JEC-JAP-BB-NH29 Chapter 1 2 3 4 5 TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF SYMBOLS INTRODUCTION EXPERIMENTAL PRELIMINARIES 2.1 Similarity Requirements ..... 2.2 Definition of Wind Load--Mean Drag Force . EXPERIMENTAL APPARATUS 3 . 1 Wind Tunnel 3.2 Flow Simulation 3.3 Model ..... . 3.4 Data Acquisition . 3.4.1 Flow Measurement 3.4.2 Drag Measurement RESULTS . . . CONCLUSION REFERENCES FIGURES . TABLES i ii iii iv 1 1 1 2 4 4 4 4 5 5 6 6 6 7 LIST OF FIGURES Figure 1 Conical Horn Antenna - Gabrial UHRlO D (Original Model) . . . . 9 2 Effect of Wind Speed on the Drag of Conical Horn Antenna (Ref. 5) . . .... 10 3 Definition of Drag and Wind Direction . 11 4 Meteorological Wind Tunnel 12 5 Wind Profile 13 6 Conical Horn Antenna Cluster 14 7 Force Balance Setup 15 8 CDA of Modified Gabrial Antenna--Run 1 16 9 CDA of Modified Gabrial Antenna--Run 2 17 10 CDA of Modified Gabrial Antenna--Run 1 and 2 18 11 Average CDA of Modified Gabrial Antenna 19 12 CDA of Modified and Original Gabrial Antenna 20 ii LIST OF TABLES Table Page 1 Drag Force on the Modified Antenna--Run 1 22 2 Drag Force on the Modified Antenna--Run 2 23 3 Drag Force on the Original Antenna 24 iii Symbol A L p u LIST OF SYMBOLS reference area drag coefficient product of drag coefficient c0 and reference area A drag force typical length for model typical length for prototype wind speed wind direction geometric scale (= L /L ) m p density of air iv 1. INTRODUCTION Wind induced loads are important parameters to be evaluated during structural analysis of microwave antennas. Theoretical prediction of the wind forces exerted on such structures is practically impossible due to a complex nature of a separated flow. The wind forces suggested in ANSI Standard ( 1) are inaccurate because of absence of considerations regarding geometric details for a specific antenna. As a result, the realistic wind forces must be based on the data obtained from the wind tunnel tests. Hoerner (2) collected data related to the drag on various bluff bodies. Some of these data can be used to estimate the drag force of a microwave horn antenna. Wind tunnel tests of horn antennas were reported by Kamei, Kimura and Matsushita (3), Poreh and Cermak (4), and Cermak et al. (5). Cermak et al. (5) compared the drag force measured for different antennas and found that the Gabrial UHRlO D antenna (shown in Figure 1) exhibited the largest drag force. The objective of the wind tunnel study presented herein was to re-evaluate the mean drag force on the Gabrial UHR10 D antenna. The original geometry of the antenna was modified and the drag force was measured. The results for the modified geometry was compared with the data presented by Cermak et al. (5). 2. EXPERIMENTAL PRELIMINARIES 2.1 Similarity Requirements Investigation of wind effects on structures are usually considered for strong wind conditions where thermal stratification of the atmo-sphere is destroyed by intense vertical mixing (6). Such flow condi-tions were modeled for the wind tunnel study described in this report. 2 The essential requirements for the physical modeling included geometric similarity for the model and the prototype antenna, and dynamic similarity for the flow. Geometric similarity was easily achieved by an undistorted scaling of the model geometry. Thus, L _!!! - A - constant L - L -p where L and L are typical lengths, respectively, for model and m P prototype structures. Generally, dynamic similarity of the flow requires equality of the Reynolds numbers for model and prototype fields. However, the drag coefficient of bluff structures becomes invariant under sufficiently high Reynolds numbers (higher than critical) found in the atmospheric boundary layer (7). The value of the critical Reynolds number was examined in the preceding study (5) for an antenna of a shape and a size similar to the antenna tested in the present study. The results from Ref. (5) are reproduced in Figure 2. The data show that the drag coefficient remains constant when the wind speed exceeds 40 fps. The wind speed in the current study was then determined to be 50 fps. 2.2 Definition of Wind Load--Mean Drag Force Time averaged drag force on a horn antenna Gabrial UHRlO D and the modified models was of particular interest in the present study. Wind-tunnel tests were performed using small-scale rigid models mounted on a platform which was also exposed to the wind. In order to evaluate the mean drag on the horn antennas, the drag contribution by the platform was separately measured and subtracted from the measured total drag on the combined structures. The net drag on the horn antenna itself shall be hereafter defined by 3 (the net drag on the horn antenna) = (the drag on the horn antenna and platform) - (the drag on the platform without the horn antenna) The above formula is merely an approximation and no attempt was made to account for the induced drag due to flow interaction between the horn antenna and the platform. Using a conventional notation, the drag force FD on the horn antenna at wind direction a is schematically defined in Figure 3. The corresponding normalized drag--the drag force coefficient--is given by where U is the wind speed, p is the air density, and A is the reference area, respectively. The value of A was represented by the area of the horn antenna and its mountings projected on a plane normal to the wind. Notice that the reference area varies with the wind direction as shown in Tables 1 and 2. An alternative presentation of the drag force appears in Tables 1 where A = projected area for the prototype antenna (square feet). The full-scale drag force FD can be computed as a product of CDA and the dynamic pressure of the approach wind F = C A * (! p D2) D D 2 where p = air density U = wind speed. 3. EXPERIMENTAL APPARATUS 3.1 Wind Tunnel 4 The experiments described in this report were conducted in the meteorological wind tunnel of the Fluid Dynamics and Diffusion Labora-tory at Colorado State University. A diagram of the wind tunnel is shown in Figure 4. This closed-circuit wind tunnel is characterized by a long (96 ft) slightly diverging test section. The test section is 6 ft 8 in. wide and 6 ft hight at the location of the turntable. The ceiling is adjustable for the longitudinal pressure gradient correc-tions. The facility is driven by a 400HP variable pitch propeller with wind speed varying continuously from 0.5 to 100 fps. 3.2 Flow Simulation Atmospheric conditions suggested by Cermak (6) were simulated in the wind tunnel by means of a biplanar grid placed at inlet to the wind-tunnel test section. The horn antenna model was placed 85 ft downstream of the grid at the location of the wind-tunnel turntable. Vertical profiles of the mean speed and the local turbulence intensity of the approach wind are shown in Figure 5. The data show that the flow characteristics are quite uniform in the region where the horn antennas were immersed (25 in. up to 45 in. above the wind-tunnel floor). The reference wind speed was monitored in the uniform flow region at a height of 38 in. 3.3 Model A 1:16 geometric scale model of the upper portion of the supporting tower, the platform and horn antennas were fabricated at the Engineering Research Center Machine Shop, Colorado State University. All the geo-metric significance of the prototype structure was preserved. 5 As mentioned in the introductory section, the major objective in this wind-tunnel study was to investigate the wind effects on the horn antenna with modified geometry. Figure 1 shows the original model of the horn antenna Gabriel UHRlO D studied by Cermak et al. (5). The effects of some geometric modifications were also studied by Cermak et al. (5). They included removal of the horizontal ribs located on the back of the horn antenna, and changes of the antenna attachment (removal of one base wing). The antenna investigated in the present study was further modified by the manufacturer (Gabriel Electronics, Inc.). The antenna was attached to a platform fastened to the upper portion of the supporting tower. The tower was made of steel to provide sufficient stiffness. The platform was constructed of an aluminum plate with the full-scale dimensions of 0.69 ft by 9 ft by 18 ft. Figure 6 is a typical view of the experimental set-up in the wind tunnel. 3.4 Data Acquisition 3.4.1 Flow Measurement The mean wind speed and the local turbulence intensity profiles presented in Section 3. 2 were measured by a single hot film probe in conjunction with a constant temperature anemometer (TSI Inc. Model 1050). The hot film probe consisted of a 0. 001 in. diameter platinum sensing element of 0. 02 in. in length. The probe was carried by a vertical traverse to measure the local wind speed at different heights above the wind-tunnel floor. The data were sampled for 32 seconds at a rate of 260 samples per second. The output from the hot film was fed to a data acquisition system controlled by a Hewlett-Packard System 1000 minicomputer. The data were then analyzed and stored using appropriate software. 6 3.4.2 Drag Measurement A strain-gaged force balance manufactured by Inca Engineering Co. was used for the measurement of the mean drag on the horn antennas. Possible experimental error in the system was examined in detail by Poreh and Cermak (4), and was found to be ±3 percent. The force balance arrangement is shown in Figure 7. The drag data were acquired at a rate of 260 samples per second for 16 seconds and processed with the data reduction system described above. For each measurement of the drag, the reference speed of the approach wind was simultaneously monitored by a pitot-static tube. 4. RESULTS The results of the study are presented in Figures 8 to 12 and Tables 1 and 2. Two experiments were performed to measure CDA for the antenna. The results of experiment number 1 (run 1) are shown in Figure 8 and Table 1. Similar data for the second experiment (run 2) are presented in Figure 9 and Table 2. The two sets of data are com-pared in Figure 10. The average of CDA, computed based on Figure 10 and Tables 1 and 2 is plotted versus the wind direction in Figure 11. It is compared with the data for the original antenna in Figure 12. The CDA data for the original antenna, Table 3 and Figure 12, was computed based on the results presented by Cermak et al. (5) (Appendix, Table A.la, p. 108). 5 . CON CL US ION The drag force, expressed by CDA' is lower for the modified Gabriel UHRlO D antenna by approximately 10 percent when compared with the data for the original antenna. 7 REFERENCES 1. American National Standards Institute, "Minimum Design Loads for Buildings and Other Structures," (1982), ANSI Standard ASS.1-1982. 2. Hoerner, S. F., "Fluid-Dynamic Drag," (1965) published by Hoerner, S. F., pp. 3.17-3.18. 3. Kamei, I., E. Kimura, and I. Matsushita, "Experimental Study of Wind Force Coefficient of SHF Antennas for Telecommunication Tower Design," (1971), Proc. of the 3rd Int. Conf. on Wind Effects on Buildings and Structures, Tokyo, Japan, pp. 357-364. 4. Poreh, M. and J. E. Cermak, "Wind Forces and Moments on Microwave Antennas," (1976), Colorado State University, Report CER76-77MP-JEC12, Fort Collins, Colorado. 5. Cermak, J. E., J. A. Peterka, B.Bienkiewicz, and N. Hosoya, "Wind Forces on Microwave Antennas, Equipment and Towers," (1983), Colorado State University, Report CER82-83JEC-JAP-BB-NH43, Fort Collins, Colorado. 6. Cermak, J. E., "Laboratory Simulation of the Atmospheric Boundary Layer," (1971), AIAA Journal, Vol. 9, No. 9, pp. 1746-1754. 7. Cermak, J. E. , "Aerodynamics of Buildings," (1976), Annual Review of Fluid Mechanics, Vol. 8, pp. 75-106. 8 FIGURES Figure 1. Conical Horn Antenna - Gabrial UHRlO D (Original Model) t-ffi t1 ~ b 8 (.') < « 0 El ALPHA a 0 A ALPHA a 120 * ALPHA a 240 E> ALPHA a 60 2.8.-------y-~------.---------,..----.:..:.:--..,_:_...:..:.::..:.::.._~:.:_ ______ _ DRAG INCLUCES PLATFORM a~ ~9 B 8 -El 1.0 a-----A~~a::===:::::: e- ---1 t "* . . • -*---------.e.-::--------_._ ________ _.__ ______ _._ _________ _._ ______ __. _____ . 28.8 48.8 68.8 88.8 REFERENCE \£01> SPEED CFPS) Figure 2. Effect of Wind Speed on the Drag of Conical Horn Antenna (Ref. 5) ...... 0 -Q) -en Wind Direction a I. 11 l Wind Drag Force F0 Force Balance 9' PLAN VIEW Conica I Horn Antenna Platform .I Figure 3. Definition of Drag and Wind Direction AUX I LI ARY I INTAKE ,,,, ,,,, ,,,,,, 55 'I rn: .. ~l ll'I\' vVIL~ AIR TEMP. 93°- 4°C ,,,, . i.I 4 - -- ---·-""r;;-+--- -- --·-t - ----. -. AIR FLOW ( VEL. 0.6-36 nv's) ~·LL--, POWER ROOM 11 ,, '',,}!.< ~:' REFRIGERATION CONTROL ---1.2 0 UNIT 150 tons ROOM  _..,. I I 1.83 UPWIND ROUGHNESS ELEMENT __... ROTATABLE VANES I '/.,J J AUX I LI A~~:. 2.06~x--£5fHAUST I 12 ---·-- ----l "--BUILDING MODEL BOUNDARY HEAT SOURCE TURNTABLE OR SINK, o0 - 149°C ' L5.5- ~~~OFLOOR 27 TEST SECTION -------------~ PLAN :---- - ~-RE~~~ 4~~T----- -----~DJUSTA;~~~Ll~G --;-;-! 'I I I~ ~ , /LONGITUOIN\OL PRESSUFUF CONTROL ;5 , --sc~ I f -j---r:r::-t:¥~~3-£7:Li-L l .II. Zll l I I I I I ,~~lw~lwwlGJI I AUXILIARY EXHAUST ALL DIMENSIONS IN m ELEVATION MOVABLE VANES INERTIAL MOUNT AND BUI LOI NG MODEL Figure 4. Meteorological Wind Tunnel ...... N HEAN VELOCITY PROFILES TURBULENCE PROFILES 60 60 a P~ID2 a PGRID2 sel a 50 a -l] a a a z 40r z 40 H a H c CJ I tl .... 30 a .... 30 a :t J: B a fJ a H H .. w w I ...... I: a J: CJ w 20 20 ... a a a a . a a a a 10 I- a 18 a .. a a t] c . a a a a 0' I I I I I I I I I 8 I ' 8 18 20 30 40 58 60 0 5 18 15 UMEAN - FPS LOCAL TURB INT - U Figure 5. Wind Profile 14 Figure 6. Conical Horn Antenna Cluster 15 Figure 7. Force Balance Setup I"\ (\I * * I-k. v < 0 (.,) E RUN 200. 9 r-,.·--------...----,.-.....--,.---,,-.....,..--...--,---..,.---y--.,·· 180.8 160.0 148.8 129.0 199.8 ae.e -s-a-e'-.. a-a-.:: a a/ "-a a-a-· "" / a, _13 ' /13 \ a m............, .,,,,,,. .. El 60.8 40.8 20.8 .0;--_..._~_.___~0-'-~-:-;.--..___._~=----_.__~__._J .0 38.0 60.0 158.8 sa.e 128.0 180.8 \ID~D DIRECTION Figure 8. CDA of Modified Gabrial Antenna--Run 1 ....... °' t"\ (\I * * t-l&. v < Q 0 r:J RUN 2 280. 8 r--r ---r---r---___,----.--..---.---~--..---...----""'! 180.0 160.0 140.8 12.0.8 100.0 80.0 -s-s- /s-s E-9 ~ ~~ " ~-~ El El/ "' . "" .El/ El / "' m__..m El / "t:i' 60.8 48.8 20.0 .fJ I I • I .0 38.0 60.0 sa.a 12a.0 JS0.0 188.8 'WIND DIRECTION Figure 9. c0A of Modified Gabrial Antenna--Run 2 ........ ...,_J n N * * .....ta.. v < 0 u El 200.6 r 180.0 160.8 *RUN 2 140.0 120.0 -EJ-EJ-8"" ....... t!r-=::j -*-*-*-i~ ~~· "·' ~i:r 100.8 ea.a ~ El/' 1!r _,.,?* '•' 60.0 40.8 20'.8 .0---'-~_._=~--'-~-'-__J~_._~-'---1~--'-~ .0 "--.-::-:--~--t.~-L~-'-~-'--_J 38.0 60.0 90.0 128.0 J50.8 180.0 WIND DIRECTION Figure 10. CDA of Modified Gabrial Antenna--Run 1 and 2 ....... ex> I"\ N * * t-la.. v < a 0 a 200.8r·~-----~-.---,____..--..,----,.~~-~.--r-~.---,--~-~,---.,..~.,..---,--1 180.8 160.0 t40.0 -B~B-E.__ /8-a-e, a-a ~El"" El---El El/ ""- . El E.1/ "" El/. El"-.. / El 120.8 100.8 88.8 60.9 40.0 20.8 .0 .0 30.0 60.0 90.0 12.0 • .0 250.0 280.0 \lIND DIRE':TION Figure 11. Average CDA of Modified Gabrial Antenna ...-"" I'\ "' * * t-"'" v < 0 0 E ORIGINAL ANTENNA * MODIFIED ANTENNA 200. 8 , ---r----r 1·-.......,...---, 1----------. ----, .------.------..-180.8 ·-160.8 140.0 120.0 sea.a 88.8 El -C\ ,El........_ El/ "' "'. a- 'd' a-El-a / ' -*-*-* ""' ef *-*--............ *· El / */ ' .......... ·-......... '~ r."t ~ .-L_....... ~ L:l~ J!I ._ ""'* El El// ""'*"'' //* "'(!] , /* ... i."'- /~* ""-~/ 60.0 40.8 20.8 I .__. ____ _ ~j .01--- . L • .....___. ' I .8 s0.0 s0.0 sa.a 128.0 J58 • .0 iaa.a \lIND D:IkECTION Figure 12. CDA of Modified and Original Gabrial Antenna N 0 21 TABLES 22 Table 1. Drag Force on the Modified Antenna--Run 1 IJ!ND O.Q 10.0 2(•. 0 30.0 4<:c. () SC-.0 6(•. Q 7C•. <.\ 8(1. () ')0.0 100.0 110.0 120.0 1 3(• . () 140.0 15Ct.O u.o. (,t 1 70. () 180.0 CC• • 96- 5 .925 .8?5 .S?S .817 . ?? 4 • 7(•(1 .£S4 • E.<) 4 .£27 . t• 1 5 .£55 .647 .123 .715 .72, . 786 .813 .830 AREA<SQ.F'T) 139.4 147.3 151.8 154.1 152.e 149. 4 142.8 133.3 121.2 1C''· 5 121.2 133.3 14 2. s 149.4 152.S 15 4. 1 1s1.e 14 7. 3 139.4 cc-~ 134.5 136.2 132.S 135. 3 124.8 115.6 9~.9 9t. 2 73.3 66.7 74.6 S7.3 92.4 1CrS.1 1(1~. 3 111. 9 11 9. 3 119. a tl 5. 7 23 Table 2. Drag Force on the Modified Antenna--Run 2 LH NO c Ce AREA(SQ.F"T) CC•A t) • 0 .926 139.4 129.1 1 (). () .SS1 147. 3 129.? 20.0 .827 1s1. e 125.5 30.0 .79£ 154.1 122.7 40.0 .795 152.S 121 . 4 50 ,() .742 149. 4 11 C1 • S ftO.O .715 142. e 102.1 ?Ct. 0 . t.5~' 133.3 S6.G 80.0 . E· 12 121. 2 74.1 9().0 .617 10t;.5 65.7 1 ¢C) • <) . E·22 121. 2 75.3 11().0 .595 133.3 ?9.3 120.0 . t·60 142.0 94.2 13() . () .6S9 149. 4 1 1.>2.9 140.0 .736 152.8 112.4 156.0 .724 15 4. t 111. 6 u.o. () .794 151. s 12 C1 • 5 17() .0 . 7S? 147.3 115.9 18(•.0 .868 13'1.4 121 . () 24 Table 3. Drag Force on the Original Antenna WIND 0.0 l(t. 0 20.0 3(•. () 4(.\ . 0 5(c. 0 £0.0 7(•. 0 80.0 9(•. Q 100.0 110.0 120.0 130.0 !40.0 150.0 160.0 170.0 1 SC• • 0 C C1 1 . (•7 6 1. (14 7 .897 . 9C•5 .SSS .819 . soo .777 . ~.99 . €·65 . 709 . 74(• 7"'' . ,.._ .828 .914 .865 .895 .986 .924 AREA<SQ.FT) 13~.4 147. 3 151. s 15 4. 1 152.e 149.4 142.S 133.3 t 21. 2 lt'H·. 5 121. 2 133.3 142. s 14,.4 152.8 154. 1 151. s 14 7. 3 139.4 CDA 15 0. 1 154.2 13 6. t 139.4 135.7 122.3 1t4. 2 103.6 S4.7 70.0 S5.9 9S.6 107.4 123.7 139.7 133.3 135.S 145.3 128., 

Drag force on microwave antenna

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Drag force on microwave antenna

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