1、NASA TECHNICAL MEMORANDUM NASA TM X-3302 Cn I- EFFECT OF WALL SUCTION ON PERFORMANCE OF A SHORT ANNULAR DIFFUSER AT INLET MACH NUMBERS UP TO 0.5 Albert J. Juhasz Lewis Research Center oUiT,o Cleveland, Ohio 44135 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. OCTOBER 1975Provided by
2、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. 2. Government Accession No. 3. Recipients Catalog No. NASA TMX-3302 4. Title and Subtitle 5. Report Date EFFECT OF WALL SUCTION ON PERFORMANCE OF A SHORT October 1975 6. Performing Organization Code
3、ANNULAR DIFFUSER AT INLET MACH NUMBERS UP TO 0.5 7. Author(s) . 8. Performing Organization Report-No. Albert J. Juhasz . E-8393 10. Work Unit No. 505-04 9. Performing Organization Name and Address Lewis Research Center11. Contract or Grant No. National Aeronautics and Space Administration Cleveland,
4、 Ohio 44135 13. Type of Report and Period Covered - Technical Memorandum 12. Sponsoring Agency Name and Address National Aeronautics and Space Administration14. Sponsoring Agency Code Washington, D.C. 20546 15. Supplementary Notes 16. Abstract The performance of a short annular diffuser equipped wit
5、h wall bleed (suction) capability was evaluated at inlet Mach numbers of 0.186 to 0.5. The diffuser had an area ratio of 4.0 and a length-to-inlet height ratio of 1.6. Test results show that the exit velocity profiles, typical of annular jet flow without suction, could be considerably flattened by a
6、pplication of wall suction. This improved performance was also reflected in diffuser effectiveness (static-pressure recov-ery) and total-pressure loss results. At the inlet Mach number of 0.5 diffuser static-pressure recovery was equal to or better than at lower inlet Mach numbers for comparable suc
7、tion rates. 17. Key Words (Suggested by Author(s) 18. Distribution Statement Combustor flow control Unclassified - unlimited . Diffuser bleed STAR Category 02 (rev.) 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of Pages 22. Price Unclassified Unclassified 22 $3.
8、 25* For sale by the National Technical Information Service, Springfield, Virginia 22161 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EFFECT OF WALL SUCTION ON PERFORMANCE OF A SHORT ANNULAR DIFFUSER AT INLET MACH NUMBERS UP TO 0.5by Albert i. Juh
9、asz Lewis Research Center SUMMARY The performance of a short annular diffuser equipped with wall suction capability was evaluated at inlet Mach numbers of 0. 186 to 0. 5. The diffuser had an area ratio of 4.0 and a length-to-inlet height ratio of 1.6. The diffuser walls were of toroidal form with qu
10、arter circle cross section. Wall bleed (suction) flow was removed through two stepped slots continuous over the wall circumference, located at 200 and 400 of arc. The performance parameters that were determined included velocity profile shapes, diffuser effectiveness (static -pressure recovery) and
11、diffuser total-pressure loss. Test results show that the annular-jet exit velocity profiles, obtained without suc-tion, could be considerably flattened by applying about 4 percent suction on the inner wall and 6 percent on the outer wall. Diffuser effectiveness at the lowest inlet Mach number was im
12、proved from about 25 percent without suction to 75 percent at a total suc-tion rate of 15 percent. At the 0. 5 inlet Mach number diffuser effectiveness was equal to or higher than at lower Mach numbers for comparable suction rates. This implies that extrapolation of test rig performance data obtaine
13、d at low Mach numbers to the higher engine design Mach numbers is justified for the diffuser geometry tested. Similar conclusions were reached from total-pressure loss results. INTRODUCTION An investigation was conducted to determine the performance over a range of inlet Mach numbers of a short annu
14、lar diffuser provided with suction capability by means of peripheral step slots in the circular arc contour diffuser walls. A second but equally important objective was to establish whether diffuser performance testing at low Mach numbers would be indicative of performance at Mach numbers of 0. 5.Pr
15、ovided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The interest in high-Mach-number gas-turbine combustor diffusers arises from axial compressor design studies as discussed for example in reference 1. Such studies indicate that increasing axial and tangen
16、tial velocities, which in turn yield higher flow Mach numbers relative to the compressor blades, would permit higher blade loading with significant gains in stage pressure ratio. As a result the number of stages to ac-complish a given overall pressure ratio could also be reduced. For example, advanc
17、ed compressors with design exit Mach numbers of 0.5 are being contemplated which would develop overall pressure ratios of 12:1 in as few as five stages. This rather drastic reduction from the usual design of eight or nine stages for this performance level, would bring about significant savings in co
18、mpressor weight, complexity, and cost. One requirement for successful integration of such advanced compressors with other gas turbine engine components is that combustor diffusers be able to operate at inlet Mach numbers of about 0. 5 without incurring severe performance penalties. Dif-fuser designs
19、 that may meet this requirement feature high area ratio at minimum length, with some form of wall boundary-layer control such as suction (refs. 2 to 6). Of course, to conserve engine, cycle efficiency, the bleed flow could also be used for addi-tional functions such as turbine cooling or cabin air p
20、ressurization (as was suggested in ref. 2). Reference 2 employed a distributed deceleration scheme over diffuser walls of circular arc cross section with two circumferential suction slots which were flush with the wall surface. A Griffith diffuser with a concentrated deceleration region located be-t
21、ween regions of constant velocity and favorable pressure gradient was used in refer-ence 3, and references 4 and 5 report results obtained with dump diffuser geometries employing different techniques of flow control by wall edge suction. Reference 6 de-scribes the performance of an asymmetric diffus
22、er using suction. In the present investigation a wall geometry similar to that of reference 2 was test-ed to evaluate performance over a range of inlet Mach numbers. The removable dif-fuser walls positioned between the diffuser inlet and exit passages were of toroidal form with quarter-circle cross
23、section. Wall bleed flow was removed through two stepped suction slots, located at 200 and 400 of arc, which were continuous over the full wall circumference. With an area ratio of 4.0 at a length-to-inlet height ratio of. only 1. 6, the diffuser was even shorter than the vortex dump diffuser of ref
24、erence 4. The inlet passage flow area was 304 square centimeters (47.12 in. 2) Velocity profiles, diffuser effectiveness (static-pressure recovery) and diffuser total-pressure loss data were obtained for nominal inlet Mach numbers of 0.186, 0.200, 0.267, .0.410, and 0.500. At the lower inlet Mach nu
25、mber data were obtained at suction rates up to 15 percent representing an estimated maximum cooling requirement for ad-vanced gas turbines. The maximum suction rate was 6 percent at inlet Mach numbers of 0. 5. Nevertheless, sufficient data were obtained to yield an indication of the inlet Mach numbe
26、r effect on diffuser performance. All testing was conducted with air at near ambient pressure and temperature. 2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SYMBOLS A area AR diffuser area ratio, A2/A1 B bleed flow fraction of total flow rate C sp
27、ecific heat at constant pressure dimensional constant H diffuser-inlet passage height L diffuser length M average Mach number at an axial station m mass flow rate P average pressure at an axial station p local pressure at a radial position R gas constant for air r wall contour radius T temperature V
28、 average velocity at an axial station v local velocity at a radial position X downstream distance y specific heat ratio diffuser efficiency, eq. (5) 77 diffuser effectiveness, eq. (3) Subscripts: i inner wall m maximum o outer wall r local value at a given radial position s isentropic condition t to
29、tal 0 stagnation3Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1 diffuser inlet station 2 diffuser exit stationAPPARATUS AND INSTRUMENTATIONFlow System The investigation was conducted in the test facility described in reference 2. A schematic of th
30、e facility flow system is shown in figure 1. Air, at a pressure of ap-proximately 100 newtons per square centimeter (145 pia) and at ambient temperature, is supplied to the facility by a remotely located compressor station. This air feeds the three branches of the flow system. The center branch, or
31、main air line, is the source of airflow through the test dif-fuser. The air flowing through this branch is metered by a square-edged orifice in-stalled with flange taps according to ASME standards. The air is then throttled to near, atmospheric pressure by a flow control valve before entering a mixi
32、ng chamber from which it flows through the test diffuser. The air discharging from the diffuser is ex-hausted to the atmosphere through a noise absorbing duct. The other two branches of the flOw system supply the two air ejectors which produce the required vacuum for the inner and outer wall diffuse
33、r bleed flows. The ejectors are designed for a supply air pressure of 68 newtons per square centimeter (100 psia) and are capable of producing absolute pressures down to 2.38 nevtons per square centimeter (7.0 in. Hg). The inner and outer diffuser wall bleed flows are also metered by square-edged or
34、-ifices. These orifices are also installed with flange taps according to ASME specifica-tion in the suction flow lines that connect the inner and outer diffuser wall bleed cham-bers to their respective ejector vacuum chambers. The maximum suction flow rate is fixed by facility limitations. Hence, th
35、e suction rate capacity, expressed as a percent-age of the diffuser flow rate, decreases from about 15 to 6 percent as the diffuser inlet Mach number is raised from 0.18 to 0.5. Diffuser Test Apparatus The annular diffuser used was essentially that of reference 2, but for a few modi-fications. A cro
36、ss-sectional sketch With pertinent dimensions is shown in figure 2. As in reference 2 the centerbody that forms the inner annular surface is cantilevered from support struts located 30 centimeters (12 in.) upstream of the diffuser inlet passage. 4Provided by IHSNot for ResaleNo reproduction or netwo
37、rking permitted without license from IHS-,-,-This construction minimized the possibility of strut flow separation having an effect on inlet velocity profile. :. Diffuser Walls . The removable diffuser walls are positioned in the apparatus as shown in figure 2. The details of the stepped slot, quarte
38、r torus wall geometry are shown in figure 3, which represents an axial section along the annular flow passage. The stepped slot geometry permits drawing off the suction flow in a direction parallel to the wall. On both the inner and the outer wall, the 0.050 -centimeter (0.020-in.) slots are located
39、 at 200 and 400 of arc measured from the start of the diverging passage. The suction flow from each of the suction slots enters the space inside the walls and is remove:d by 12 equally spaced short pipes of 1.5 centimeters (0. 62 in.) inside diameter. These pipes duct the inner wall bleed flow to th
40、e inner wall suction plenum and the outer wall bleed flow to the outer wall suction.manifold(fig. 2) .The threads on these pipes also provide. a methodfor mechanically fasteningthe diffuser walls in the desired position Diffuser Instrumentation Theessentiall diffuser instrumentation isindicated,.in
41、figures 2 and 3. Diffuser-inlet total pressure was obtained from three five-point total-pressure rakes equally spaced around the annular circumference. Inlet static pressure was measured using wall taps in the vacinity of the inlet rakes. , Diffuser-exit total and static pressures were obtained by u
42、sing three nine-point pitot static rakes that could be rotated in a circumferential direction and translated ax- ially. The circumferential spacing between the rakes was fixed at 120. For this in-vestigation these rakes werpositiond a distane equal to twice theinlet passage height from the- start of
43、 the diffusing section, since this position was assumed to repre sent the location of the dome in an annular gas turbine-type combustor. All rake pres-sures were measured isingthreeScanivlves, each ducting pressures from a maximum Of 48 ports tb a flush mounted 0.69 newton per squarcetimeter (1.0 ps
44、id) strain gage transducer. The valve dwell time at each port was 0 2 second, or over three times the interval required toieach steady state. Continuous calibrationbf the Scani-valve system was provided by ducting known pressures to several ports. Visual display of pressure profiles was madeavailabl
45、e by also connecting all inlet rakes and two exit rakes to common well manometers The manometer fluid was dibutyl phthalate (specific gravity, 1.04. All other pressure data such as orifice line pressures for the main air line and theProvided by IHSNot for ResaleNo reproduction or networking permitte
46、d without license from IHS-,-,-subatmospheric bleed-air lines were obtained by use of individual strain gage pressure transducers. The temperatures of the various flows were measured with copper con-S stantan thermocouples. All data were remotely recorded on magnetic tape for subsequent processing w
47、ith a digital data reduction program. In addition any test parameter could be displayed in the facility control room by means of a digital voltmeter. PROCEDUREPerformance Calculations Using the digital data reduction program mentioned previously, the overall diffuser performance was evaluated in ter
48、ms of the radial profile of exit velocity, diffuser effec-tiveness, total-pressure loss, and diffuser efficiency. The values of the last three fig-ures of merit were expressed in percentages. Intermediate computations included aver-age static and total pressures, local and average Mach numbers and l
49、ocal- to average-Mach-number ratios; that is, the equivalent of the local- to average-velocity ratios. The average pressures and Mach numbers at the diffuser exit P 2 , P02 , and M2 were computed by trapezoidal integration using area ratio weighed pressures at the various radial positions. At the diffuser inlet straight arithmetic averags were com
