1、NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL NOTE No. 1695 EFFECT OF PRESSURE RECOVERY ON THE PERFORMANCE OF A JET-PROPELLED AIRPLANE Bypercent decrease in 6p8CifiC fU81 consumption. From these and other similar effects indicated in the performance analysis, it would appear that the attainm
2、ent of high ram recovery should be given magor consideration. The analysis shqs further that ram recovery will become of greater importance in obtaining optimum performance as airplanes are developed which have higher dragdivergence Mach numbers and which utilize mre powerful Jet engines. IIWRODUCTI
3、OW Because Of the development Of th8 turbojet engine and increasing airplane speeds, the problem of taking in the air and ducting it to the compressor inlet with a minimum pressure loss has assumed a greater im and other commonly used parameters will be reviewed and compared with ram-recovery ratio.
4、 c It was considered that an efficiency parameter, to adequately indicate the pressure losses of an air-induction system, should have the following characteristics: 1. Be readily measurable 2. Rave a maximumvalue of unity (or 100 percent) to indicate the maximum possible theoretical efficiency, or t
5、he case of zero pressure loss 3- Remain essentially constant for the subsonic-speed range (provided there are no energy losses due either to shock formation or separation resulting from changes in Reynolds number) Rasrrecovery ratio.- A parameter, used by many to indicate the performance of an air-i
6、nduction system, especially at Mach numbers up to 1.0, is the ratio of the impact (or ram) pressure recovered to the impact pressure available (22) The mximumvalue of this parameter cannot be greater than 1.0; and it is readily measurable. To determine the constancy of ram-recovery ratio with Mach n
7、umber, . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NACA TR No. 1695 -. experimental data have been used. .These date were obtained by I?eumsnn (reference 1) from tests of diffusers at high subsonic speeds. It may be aeenln figure 1 that ramec
8、overy ratio, cpmputed from these test results, varied negligibly up to a Mach number of 0.90. A similar negligible change was found for a pllach nuniber range from 0.30 to 0.875 in tests of an NACA submerged-inlet installation. W recovery ratio, therefore, meets completely the criteria previously li
9、sted. Dynamic pressurecovery ratio.- El -30 The quantity q. or 1 -a is sometimes used in presenting pressure losses, especially g0 . at low subsonic Mach numbers. It has, however, several disadvantages. The ratio “- o can have values either less or greater than 1.0, 90 the latter usually being the c
10、ase for high Mach numbers and low pressure losses. Figure 1 shows that, for a given air-induction system, this representation of the experimental pressure losses does not remin constant with increasing Mo. Dynamic pressure-recovery ratio is related l to ranrrecovery ratio by the compressibility fact
11、or (1 + q). . . Total-pressure ratio.- One parameter-which has direct application in turbpjet-performance calculations is the ratio of the total pressure at the compressor inlet to the free-stream total pressure, =lb,. It is related to ranerecovery ratio by the foilowing expression: Y =I - pQ 1 (+2p
12、 -1 1 +l 3 5 =* - PO =o Y - * (1 + y+ Mo2)7-1 which is derived in Appen q2 The variation of this energy ratio with Mach number for constant values of ran+re covery ratio is shown in figure 4. The energy ratio has been tiown under e variety of different names end forms. Some authors refer to it as an
13、 energy efficiency, while others call it a diffuser efficiency. It is equivalent to the adiabatic compression efficiency commonly used to denote supercharger and blower performance. (See reference 2.) The principal disadvantage of using energy ratio to present air-inductior+system losses is that it
14、involves relatively compliceted computation. Figure 1 shows that expertental losses given in this manner have 8 slightly greater variation with Mach number than does ram-recovery ratio. From the preceding rlnduction system till d8p8nd only ou the Mach numb81 and on the efficiency with which the flow
15、 process takes pkC8. !Che total temperature ratio between the diffused and the ambient air will depend solely on the airplane Hach llUPib8r. slcuLations of the performance of a typical jet engine wBre lgade for various altitudes and airspeeds by determ$ning for these conditions th8 total t8mpereture
16、 and, for various ram-rrecovery ratios, the total preseure 7 ratio from 0.70 to 0.90, the percentage Thus the fuel consumption per mile is increased and the range is reduced. The following table gives the percent of rated rotational speed of the jet-engtie and the cruising velocity, at a point durin
17、g flight for maxim range where the fuel has been consumed. Raz+recovery ratio 20,000 feet 40,000 feet Hi - P, =o - PO vO Percent N To- Percent N 0.x) 361 85.0 399 89.7 .60 368 83.7 86.9 1.00 370 82.3 E 84.7 CONCLTJSIONS In an analysis of the effect of pressure recovery on the performance of a jet-pr
18、opelled airplane, it is shown that: . 1. Ram-recovery ratio HI - P, Ho - PO was the parameter most suitable to indicate themefficiency of the air-induction system. 2. Reduction ti ram-recovery ratio considerably reduced the net thrust and increased the specific fuel consumption of the typical jet en
19、gine. 3* The resultant effects on the performance-of a fighter-type airplane powered by this typical jet-engine were of sufficient magnitude to make high efficiency of the air-induction system of - major importance. 4. As airplanes are developed which have higher draivergence Mach numbers and which
20、utilize more powerful jet engines, high ram- recovery ratios for the aii-induction systems will become even more necessary, if maximum performance is to be realized. . Ames Aeronaut Jonas, Julius: Jet Airplane Range Considerations. Jour. Aero. Sci., vol. 14, no. 2, Feb. 1947, pp. 12b128. Provided by
21、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1 too - 0 -z .96 a 0 . -. . 1 d?4 0 ./ .2 .3 .4 .5 .6 .7 .8 .9 IO . F0 with ff * Figure 4 Computed woriof/on of energy rot/o with free-sfreum * _ MU Rum-recovery folio, LOO. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
