1、The Engineering Society AEROSPACE PRACTICE RECOMMENDED Ih A =For Advancing Mobility Land Sea Air and Space 400 COMMONWEALTH DRIVE. WARRENDALE, FA 15096 Submitted for recognition as an American National Standard L t I ARP 996A Issued 8-31-67 Revi sed 11-86 Superseding ARP 996 COOLING DATA FOR TURBINE
2、 ENGINES IN HELICOPTERS 0 TABLE OF COtdTENTS 1. 2. 2.1 2.2 2.3 3. 3.1 3.2 3.3 4. 4.1 4.2 4.3 4.4 8 4.5 5. 5.1 5.2 5.3 SECTION PAGE - PURPOSE . . *. . . . . . . . . . . . . . . . . . . . . 3 SCOPE. 3 klethod . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Axial Nacelle Air Flow . , . . . . .
3、. . . . . , . . . . . . . . 3 Transverse Nacelle Air Flow . . . . . . . . . . . . . . . . . . 3 DEFINITION OF TERMS . . . . . . . . . . . . . . . . . . . . . . , , 3 Nomenclature . . . . , . , . . . . . . . . . . . . . . . . . . . 3 Subscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4、3 Definition of Input for Listed Programs . . . . . . . . . . . . . 4 DATA TO BE SUPPLIED BY THE ENGINE MANUFACTURER . . . . . , . . , . 4 Accessory Temperature Limits . . . . . . . . . . . . . . . 4 Engine Skin Temperature Presentation . . . . . . . . . . . . . . . 4 Power Conditions . . . . . . .
5、. . . . . . . . . . . . . . . . 4 Accessory Temperature presentation . . . . . . . . . . . . . . . . 5 Zonal Heat Rejection Rates . . . . . , . . . . . . , , . . . . . . 6 CALCULATIONS TO BE PERFORMED BY THE AIRFRAME MANUFACTURER . . . . 6 Cool ing Air Required . , . . . . . , , , . . . . . . . . .
6、. . , , 6 Samples Given . . . . . . . . . . . . . . . . , . . . . . , . G CautionsNoted . . 7 SAE Technicai Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use Qf this report is entirely voluntary, and its applicability and s
7、uitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.“ SAE reviews each technical report a least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Co
8、pyright 1986 All rights reserved. Society of Automotive Engineers, Inc. Printed in U.S.A. .- . SAE ARPm97bA b = 357340 003042 2 m ARP 996A SE Page 2 TABLE OF CONTENTS (Continued) PAGE . SECTION 6 . AXIAL NACELLE AIR FLOW 7 6.1 talculation 7 6.1.1 Correlations for Convection Heat Transfer Coefficient
9、s 11 6.2 Example Problem 11 6.2.1 Machine Computer Programs . 17 6.2.1.1 Program 1 . 18 6.2.1.2 Program 2 . 19 6.2.1.3 Program 3 . 20 7 . TRANSVERSE NACELLE AIR FLOW 21 7.1 Calculation 21 7.1.1 Natural Convection 22 7.1.2 Forced Convection . 22 7.2 Example Problem 23 7.2.1 Natural Convection . . 23
10、7.2.2 Forced Convection . 26 PREPARED BY SAE COMMITTEE S.12, HELICOPTER POWERPLANT 5 Page 3 AR? 996A I 1. PURPOSE: Efficient design of a turbine engine installation requires data on the ways the engine rejects heat, the temperature limits of various parts of the engine, and the changes in heat rejec
11、tion from service, as well as a method of using these data. and use is needed. subject to full scale testing for verification. A uniform, practical method of data presentation Cooling margins developed by these methods would be 2. SCOPE: - 2.1 Method: A tested method of data presentation and use is
12、described herein. Thethod shown is a useful guide, to he used with care and to be improved with use. 2.2 Axial Nacelle Air Flow: Machine computer programs and an example problem are given for axial nacelle air flow. 2.3 Transverse Elacelle Air Flow: Calculation is given for natural and forced convec
13、tion with example problems. 3. DEFINITION OF TERMS: 3.1 Nomencl ature: A = Area, ft* = Specific heat, Btu/lb deg F dP = Equivalent diameter of annulus, ft h = Heat transfer coefficient, Rtu/hr ft2 deg F k = Thermal conductivity, E?tu/hr ft deg F Ke = Effective conductance of shell, Btu/hr ft2 deg F
14、Npr = Prandtl Number NRE = Reynolds Number S T = Temperature, deg R V = Velocity, ft/hr i4 = Weight flow, lb/hr X = Axial distance from entrance or flow disturbance, ft tq = Equivalent emissivity for radiation between cy1 indrical shells. U = Stefan Boltzmann constant ct = Absolute viscosity, lb/ft
15、hr p = Density, lb/ft3 q = Heat flux per unit length, Ptu/hr ft D2 - Dl = Radial spacing in annulus, ft = -7 This quantity includes the view effects and the emissivities 3.2 Subscripts: a = Relating to fluid a b = Relating to fluid b la = Relating to surface of shell 1 on the side toward fluid a 2a
16、= Relating to surface of shell 2 on the side toward fluid a 2b = Relating to surface of shell 2 on the side toward fluid h i = Zone number SAE ARPxSbA 8b W 83573i.10 0030484 b ARP 996A Page 4 3.2 (Continued) : IN = At inlet of zone e = Effective r = Radiation sink 3.3 Definition of Input for Listed
17、Programs: A = Mean air temperature of zone, deg R Al A2 A3 C D = Equivalent diameter of zone, ft El E2 = Nacelle emissivity for zone, dimensionless H9 K L = Length of zone, ft M1 = Viscosity, lb/ft hr N1 = Prandtl number, dimensionless Q R T = Nacelle temperature, deg R T1 T3 W z, z1, 22, 23 = Conve
18、rgence criteria = Flow area of zone, ft* = Surface area of engine zone, ft* = Surface area of nacelle zone, ft2 = Specific heat, Btu/l b deg R = Emissivity factor for zone, dimensionless = Nacelle heat transfer coefficient, Btu/hr ft* deg R = Thermal conductivity, Btu/hr ft deg R = Heat rejected, Bt
19、u/hr ft = Laminar heat transfer coefficient of zone, Btu/hr ft2 def F (from equation 2a) T = Air temperature into zone, deg R = Engine surface temperature, deg R = Ambient air temperature, deg R = Air weight flow, lb/hr 4. DATA TO BE SUPPLIED BY THE ENGINE MANUFACTURER: 4.1 4.2 4.3 Accessory Tempera
20、ture Limits: Maximum temperature limits for accessories must be specified at designated locations on the accessories. Engine Skin Temperature Presentation: producing parts of the engine must be calculated in each zone as a function of heat rejection rate. as in Fig, 1 and are to include engine zone
21、designation, engine accessory heat rejection data, and flange leakage data. surface emissivity is supplied versus engine length, as plotted in Fig. 2. The skin temperature of the heat These results are to be presented in graphical form Also, the range of engine Power Conditions: The heat rejection d
22、ata presented shall be identified as measured or estimated and shall be for the following conditions: (1) Maximum power, Sea level, 103 F day (2) Maximum power, Sea level, 130 F day (3) Maximum power, 6000 ft altitude, 95 F (4) Maximum power, Sea level , standard day SAE ARP*hA 86 = 8357340 0030485
23、8 ARP 996A I 4.4 Accessory Temperature Presentation: For the case of accessories on the surface of the engine, the specified surface temperature and heat generation curves may be altered as shown by the dashed lines on the graph and nay increase or decrease surface temperature. 8 q, heat relected/It
24、 of ergiae leo#h -/, . I/ I I I l Zone a Zone b Zone c Zone dZone e Eng-ine Length, L FIGURE 1 Engine Surface Temperature Versus Engine Length for Various Amounts of Heat Rejection I J EngineLength, L FIGURE 2 Engine Surface Emissivity Versus Length , SAE ARPm996A 86 83573qO 0030L186 T I I ARP 996A
25、Page 6 EAE - 4.5 Zonal Heat Rejection Rates: Engine heat rejection due to flange leakage and from accessories and components must also he provided. Figure 3 provides a graphical method of presenting this within each appropriate engine zone and il lustrates the heat rejection rates when these zones a
26、re compartmented. Engine flange leakage is to be separately identified with the flange leakage rates at specific axial and circumferential positions of the engine. Heat Rejection Btu/Hr. s2b - 1 .- I Accessory Heat Rejection I i Zone at Zone b Zone IC Zone d ENGINE LENGTH L FIGURE 3 Zonal Heat Rejec
27、tion Rates 5. CALCULATIONS TO BE PERFORMED BY THE AIRFRAME MANUFACTURER: 5.1 Cooling Air Required: The amount of cooling air required must be calculated to maintain the temperature of the engine accessories within acceptable limits, or maintain maximum requested engine skin temperature, as well as p
28、roviding cooling for airframe components which may require it, such as hoses, structure, and cowling. Calculations must be carried out both for cooling air required to maintain engine component temperatures with the engine running throughout its operating envelope of ambient temperature and pressure
29、s and after shutdown. after shutdown and this condition may well become the critical case. General ly only convecti ve f 1 ow i s avai 1 ab1 e 5.2 Samples Given: Two sample calculations are given in paragraphs 6 and 7. The first is for axial nacelle air flow and the second is for transverse air flow
30、. D D D SAE ARPm9bA 8b 8357340 O030487 I = EAE Page 7 -a ARP 996A 5.3 Cautions Noted: Some of the radiation equations used in the heat transfer calculations may be ignored if, with experience, it can be seen that these effects are small. By the same token more extensive evaluatton of the engines ext
31、ernal film coefficients and surface areas may have to be considered if it is shown that these effects are predominate in determining . the engine heat rejection rates. The potential for error exists if struts, baffles or shields are encountered and changes in surface conditions in service use such a
32、s dirt or grease can substantially alter the emissivity of the surface. 0 6. AXIAL NACELLE AIR FLOW: 6.1 Calculation: The following calculation to determine the cooling air weight flow and the nacelle temperature is made by assuming the engine to be divided into several axial lengths and then perfor
33、ming a calculation for each section. section, they are all related to each other and must be analyzed interdependently . Since each section depends upon what happened in the upstream Fig. 4 is a sketch of an engine in an enclosure which has been divided into axial sections. Heat Rejected = Radiation
34、 + Convection - A - 41 2i lhe11 2 a Shell 1 Shell 1 Shell 1 For the case of transverse flow, see paragraph 7. Substituting the expressions for convection and r A heat balance for arbitrary section i, shell I, is as follows: t tra diation h Li qli = hl ai 1 li fii - Tai sfer 12 OA1 t41i - T45) t i SA
35、E ARPmbA 86 8357340 0030488 3 W Page 8 ea= -0 ARP 996A 6.1 (Continued) : Similarly for Shell 2. Heat transfer coefficient is a function of weight flow and may be substituted into the equations as h = f(W), Ambient Air (Fluld b) Enclosure I I I /(Shell 2) I l I I I I I I I 1-1 1 i i ici I Enginesurfa
36、ce Cooling Air I (Fluid a) I I I /(Shell i) I- I Hot Gas I l I I l 1 I I FIGURE 4 Paragraph 6.1.1 suggests possible correlation for h. From the graph of q versus L, q1 is obtained. Tai is the average air temperature of zone i. i SAE ARPxbA 8b W 8357340 0030487 5 W - Page 9 =;“r“, I ARP 996A 6.1 (Con
37、tinued) : Another heat balance expressing the heat gained by the cooling air may be written. i + TOUT 2 T= ai The three unknowns-Ta, T2 and W-may be found from solving equations (2) through (4) simul taneously. Since each downstream section is affected by the section upstream from it, section 1 must
38、 be calculated first and then the others in sequence. From equations (2) through (41, the flow Wal for section 1 and the air temperature, Tais may be calculated. This weight flow is that which is needed to remove the heat rejected at section 1, qal. calculation to section 2, the weight flow Wa2 may
39、be calculated using Applying the + 2 (T - TIN) in equation (4). al Tai IN = TIN If Wa2 Wat, Wa? must be used for the weight flow and Wal must be discarded since it is not large enough to satisfy the cooling requirement of section 2. Using Ta2, section 3 may be Calculated, the same process being repe
40、ated. Obviously section 1 will be overcooled, but this is necessary so that section 2 or some later section will be adequately cooled. - TaZIN) for the If Wap 2000, i ia) h = 0.023 NRE If NRE 2000 to start the calculation. From paragraph 6.1.1: 0.8 = ( 0.046)(0.27 24;2;62,664,122 DATA O. 1, O. 1 ,O.
41、 1,2.03 END 6.2.1.3 Program 3: Solves equation (3) and equation (4) when W is known. PROGRAM 3 NONJON 15:41 SCH THU 4/28/6 REH SOLN OF SIMEQ (NONLIdEAR) REM B. BRADDY X353!d REM PROGRAM NUMBER 3 5 51 52 SAE ARPm99bA Ab m 8357340 0030501 2 m - I +A* Page 21 -a ARP 996A I 6.2.1.3 (Continued) : 1 11 12
42、g 140 15 17 18 i90 2Q 21 2 20 23 24 2% 26 270 28 2% 3 3 1 330 332 334 34 350 351 352 353 999 READ K,D,A1 ,Ml,Nl,Tl,A2,El,H9,A3,T3,E2T,C,L ,T,W,Z LET B =0.23*(K/D)*(D/(Ml*Al)r0.8)*Nl f0.4 LET C1 = AZ*Tl*B LET S = 0.1713E-8 LET C4 = El*S*A2 LET 02 = C4*Tlf 4+H9“A3*T3+EZ*S*T3 +4*A3 LET D3 - C4+EZ“S*A3
43、LET C5 B*A3 LET C6 = H9*A3 LET D5 = B*(A2+A3) LET D6 = 2*C LET D7 = D6*TQ LET U = Cl*W fO08+D7*W LET V = D5*W t0,8+D6*W LET A = (D3*T t 4+C5*W CO.8*T*C6*T-D2)/(C5*W t 0.8) LET A6 = (4*D3*Tt 3+C5*LI t0.8+C6)/(C5*W f0.8) LET H = U-V*A+C5*W +0,8*T LET H1 = -V*AG+C5“W t0.8 LET T = T-H/H1 LET A = (D3*T +
44、4+C5*W .8*T+C6*T-D2)/(C5*W f 0.8) PRINT “AIR TEMPERATURE-DEG. R =I A PRINT “NACELLE TEMPERATURE-DEG. R =I T - IF ABS (H/H1) Z THEN 26 GO TO 959 DATA O,l68,0.16667,027,0,O52,0.7 RATA 960,6.28,0.36,2,7.33 DATA 56,O .8, SS, O . 24,2 DATA 664,199,O.l END 7. TKANSVERSE NACELLE AIR FLOW: 7.1 Calculation:
45、Transverse cooling may be used in certain regions of the engine outer shell. With this method cooling air will enter the annulus between inner and outer shells and travel peripherally to the exit port. Schematically, this cooling nietkod is shown in Fig. 6. The patti lengths shown are semi-circular.
46、 Shorter path lengths may be used, and the sections joined together as in the case of axial flow shown previously. This would allow circumferential variations of engine heat transfer co-efficients and temperatures, Also, the nacelle itself is a heat rejecting shell with circumferential Variations in
47、 heat transfer coefficients and temperature. inclusion at this time. Accordingly, the simple model shown will be treated. These situations are not known to require it should be adequate for most applications. SAE ARP*77bA Bb 83573L10 0030502 L1 I ARP 996A Page 22 4- 7. Air Out ? t t I b -I -I- f Eng
48、ine Surface Alr In Air Out FIGURE 6 The same basic axial flow equations, equations (21, (31, and (41, in paragraph 6.1, can be applied to the transverse cooling case. transfer coefficient equations presented in paragraph 6 do not apply for the flow between shells 1 and 2. The heat Heat transfer to t
49、he coolant circulating in the peripheral direction may be by natural convection: i.e., relying upon the density gradients existing in the annulus, or by forced convection, which requires a prime mover to circulate the cooling air. For this cooling method, the following relationships may be used to evaluate heat transfer coefficients for either natural or forced convection type flows. .l Natural Convection: 1/4 - ) = 0.27 (g) Btu (hr - ft2 - deg F where: AT = temperature difference betwee
