1、NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL NOTE 3663 DISCHARGE COEFFICIENTS FOR COMBUSTOR -LINER AIR -ENTRY HOLES I - CIRCULAR HOLES WITH PARALLEL FLOW By Ralph T. Dittrich and Charles C. Graves Lewis Flight Propulsion Laboratory Cleveland, Ohio Washington April 1956 Provided by IHSNot fo
2、r ResaleNo reproduction or networking permitted without license from IHS-,-,-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL NOTE 3663 DISCHARGE COEFFICIENTS FOR COMBUSTOR- LINER AIR- ENTRY HOLES I - CIRCULAR HOLES WITH PARALLEL FLOW By Ralph T. Dittrich and Charles C. Graves SUMMARY An experi
3、mental investigation was conducted to determine the effects of various geometric and flow factors on the discharge coefficients for circular holes having flow parallel to the plane of the hole. ric and flow factors considered were hole diameter, wall thickness at the 01 I hole, parallel-flow duct he
4、ight, boundary-layer thickness, parallel-flow u velocity, static-pressure level, and pressure ratio across the test hole. The geomet- I+ m Discharge coefficients, corrected for pressure-ratio effects, were correlated with a flow parameter incorporating the total and static pres- range investigated,
5、the effects of hole diameter and wall thickness at the hole on discharge coefficients were small compared with the effects of parallel-flow velocity and static-pressure ratio across the hole. The effects of duct height, boundary-layer thickness, and static-pressure level were negligible. U sures of
6、the discharge jet and of the parallel-flow stream. Within the INTRODUCTION Knowledge of the discharge coefficients of combustor-liner wall openings is essential in $he calculation of total-pressure loss and liner air-flow distribution for turbojet and can-type ram- jet combustors. Ac- cordingly, one
7、 phase of a research program being conducted at the NACA Lewis laboratory on combustors is concerned with the determination of the discharge coefficients of these openings. This report covers an investi- gation of the discharge coefficients for circular holes. The discharge coefficient of a square-e
8、dged, thin-plate orifice, where the flow is normal to the plane of the orifice, is a function of the geometry of the flow passage and orifice as well as the flow condi- tions (ref. 1). Geometric factors include orifice diameter and thickness as well as duct diameter and straight length; flow factors
9、 include Reynolds and Mach numbers. For air admission holes in typical combustor Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3663 m liners, however, the flows in the passage outside the liner (external flow) and inside the liner (internal
10、 flow) are essentially parallel to the plane of the opening. Under these conditions, additional geometric and flow factors must be considered. These include (1) the geometry of the hole relative to that of the external- and internal-flow passages, (2) the external and internal velocities relative to
11、 the jet velocity, (3) the external- and internal-flow densities, and (4) the external- and internal-velocity profiles (refs. 2 to 6). w (D UI rp Previous investigations (refs. 2 to 6) of the discharge coefficients for holes with parallel flow have been confined to the study of the ef- fects of flow
12、 velocities and hole diameter and were limited in range of operational variables. In these investigations, it was found that hole discharge coefficients vary appreciably with both internal and external parallel flow. ics, the effect of the various other geometric and flow factors on the discharge co
13、efficient of liner wall openings must also be known. However, for a complete analysis of combustor aerodynam- This investigation supplements existing data for the discharge coef- ficient of circular holes with parallel flow. factors studied, with their ranges, are as follows: 0.125 to 1.50 inches, (
14、2) external-flow passage height, 0.74 to 2.23 inches, (3) wall thickness at hole, 0.040 to 0.500 inch, (4) external- parallel-flow velocity, 0 to 500 feet per second, (5) static-pressure drop across test hole, 1.0 to 470 pounds per square foot, (6) boundary- layer thickness of external-parallel-flow
15、 stream, 0.040 to 0.100 inch, and (7) static pressure of external stream, 1060 to 3605 pounds per square foot absolute. The airstream temperature was approximately 75 F. For the present tests the internal parallel flow was zero. references 2 and 4 indicate that the data should be applicable to the c
16、ase of combined internal and external parallel flow provided the jet velocity is greater than the internal- parallel-flow velocity and the correct jet-outlet static pressure is used. The geometric and flow F (1) hole diameter, 4 The results of The data are correlated on the basis of flow parameters
17、and show the magnitude of the effect of the geometric factors on the discharge coefficients of circular holes. SYMBOLS The following symbols are used in this report: Ad area of duct cross section, sq ft Ah area of circular hole, sq ft d 4 Provided by IHSNot for ResaleNo reproduction or networking pe
18、rmitted without license from IHS-,-,-P Lo cn K) - NACA TN 3663 3 C cP CP,a CP?b CP,t P C g J d pd Pj Td d 3 wth wh f% pj discharge coefficient, ratio of measured to theoretical flow through hole discharge coefficient, corrected for pressure ratio effect discharge coefficient, corrected for pressure
19、ratio effect, for a given wall thickness discharge coefficient, corrected for pressure ratio effect, for a 0.040-inch-thick wall discharge coefficient, corrected for pressure ratio and wall thickness effects specific heat of air at constant pressure, 0.24 Btu/lb/OR acceleration due to gravity, 32.2
20、ft/sec 2 mechanical equivalent of heat, 778 ft-lbs/Btu total pressure of duct air, lb/sq ft abs static pressure of duct air, lb/sq ft abs static pressure of jet air, lb/sq ft abs total or stagnation temperature of duct air, OR velocity of approach stream at hole in duct, ft/sec velocity of jet, ft/s
21、ec theoretical mass flow of air through hole, lb/sec measured mass flow of air through hole, lb/sec mass density of air at duct static pressure and temperature, slugs/cu ft slugs/cu ft slugs/cu ft mass density of air at duct total pressure and temperature, mass density of air at jet static pressure
22、and temperature, Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NACA TN 3663 APPARATUS Test Sect ion A sketch of the apparatus used for the study of discharge coeffi- cients for circular holes having external parallel flow is shown in fig- ure 1.
23、The inlet of the 4-inch square duct was connected to either the laboratory air-supply system or room air, and the outlet was connected to air-flow rate were controlled by means of valves located upstream and downstream of the test section. Methods for varying test-hole diameter, test-plate thickness
24、, duct height, and boundary-layer thickness were in- corporated in the design of the test section. of one wall of the test-section duct was replaced by a 0.040-inch-thick metal plate containing the square-edged test hole. The test plate was located flush with the inside of the duct wall, reinforced
25、on the downstream side by a metal frame, and held in place and sealed along its edges by a high-temperature sealing wax. Although the face of the test plate was flat rather than curved as in combustor liners, the effect of this difference in hole geometry on the discharge coefficient for a cir- c cu
26、lar hole was assumed negligible. A plenum chamber enclosing the test plate was connected to the low-pressure exhaust system through a flow control valve and an air metering system. CA W UI Ip the laboratory low-pressure exhaust system. The duct static pressure and A portion (4.0 by 8.5 in.) Four 0.0
27、40-inch-thick test plates having nominal hole diameters of 0.125, 0.25, 0.75, and 1.50 inches were used. The plates with 0.125- and 0.25-inch-diameter holes contained five holes each. These holes were spaced 1/2 inch apart, center to center, along a line normal to the duct axis. The multiple holes w
28、ere used to maintain flow rates in a range of sufficient accuracy. For the larger holes (0.75- and 1.50-in. diam. ), a single hole was used. Plate thickness at the 0.75-inch-diameter test hole was varied by coaxially attaching a ring of the desired thickness and having an inside diameter equal to th
29、at of the test hole to the low- pressure side of the test plate. Duct height was varied by mounting wood blocks of the desired thick- ness inthe duct opposite the test-plate wall (fig. l(a). end of the blocks (contraction section) had an elliptical profile with a major- to minor-axis ratio of 2. of
30、the contraction section to the center of the test hole was 2.75 inches for test, holes 0.75- inch diameter and smaller. With the 1.50- inch- diameter test hole, this distance was 6.75 inches for a test with a 0.74- inch duct height and 9.75 inches for a test with a 2.23-inch duct height. A 30-mesh s
31、creen was located at the test-section upstream flange in order to provide a uniform velocity distribution. The upstream The distance from the downstream end In order to vary the boundary-layer thickness, the test apparatus The test plate was mounted on a was modified as shown in figure l(b). Provide
32、d by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3663 5 + m 0, M partition member and immersed 1/4 inch into the duct stream, thereby forming a boundary-layer bleedoff slot at its upstream edge. This parti- tion member, which was sandwiched between t
33、he test section and the plenum chamber, isolated the boundary-layer bleedoff air from the test-hole air. The boundary-layer bleedoff passage was connected to the laboratory low- pressure exhaust system through a flow control valve and an air metering s ys t em. Instrumentation A measurement of duct
34、pressures as close to the test hole as possi- ble was desired because of total- and static-pressure variations along the approach duct due to wall friction and changes in velocity profile. ever, preliminary pressure surveys indicated that, with a large hole and small duct-height configuration and a
35、given duct total pressure and ve- locity, the static pressure at the duct wall opposite the center of the test hole varied with flow through the test hole. Therefore, total and static pressures were measured at stations located 3- inches upstream of the center of the 1.50-inch-diameter hole and 1 in
36、ch upstream of the test holes having diameters 0.75 inch and smaller. Pressures at these up- stream stations remained constant throughout the range of test-hole air flows with all configurations investigated. How- 1 4 The probe used for determining duct total pressure and boundary- layer profile is
37、shown in figure l(a). tubing having a 0.020-inch outside diameter and a 0.002-inch wall thick- The probe tip was made from 7 ness flattened to 0.010 inch and measured inches from the probe stem axis. A traverse of a portion of the duct was possible by rotat- ing the probe stem through a small angle.
38、 Reference 7 indicates that a thin-wall, blunt-nose -total-pressure tube is insensitive to misaiine- ment between tube and stream within the range of *11 degrees. The probe stem was electrically insulated from the test section in order that, as the probe stem was rotated, contact of the probe tip wi
39、th the duct wall could be indicated by electrical continuity. Positioning of the probe tip in the duct was controlled by a micrometer acting upon a lever which rotated the probe stem. Jet static-pressure taps were lo- cated on the downstream face of the test plate as shown in figure l(a). The locati
40、on of the jet static-pressure taps was not critical in the absence of parallel flow on the downstream face of the test plate. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 Hole diam., in. 0.125 .125 .25 .25 .75 .75 .75 .75 .75 1.50 1.50 NACA TN 3
41、663 Test-plate thickness, in. 0.040 .040 ,040 ,040 .040 .125 .500 .040 .040 .040 .040 PROCEDURE Hole discharge-coefficient and boundary-layer-profile data were Duct static pressure, lb/sq ft abs obtained for the following series Boundary- layer bleedoff of tests: Number of holes 5 5 5 5 1 1 1 1 1 1
42、1 Duct height, in. 1.98 2.23 2.23 1.98 2.23 2.23 2.23 2.23 2.23 .74 2.23 19 10 1910 1910 1910 1910 1910 1910 1060 3605 1910 1910 Yes No No Yes No No No No No No No Each test series was run at external-parallel-flow velocities of 0, 40, 70, 150, 300, and 500. feet per second. At each velocity conditi
43、on. the static-pressure difference across the test hole _was varied from 1.0 to 470 pounds per square foot, when practical. was approximately 75O F for all tests. The duct-air temperature CALCULATIONS The discharge coefficient measured mass flow to the theoretical mass flow through the hole The theo
44、retical mass flow wth velocity Vj, the Jet density pj, and the hole area Ah. Assuming isentropic flow, the jet velocity Vj and the jet density pj were de- termined from compressible-flow relations utilizing the duct total pres- sure Pd and total temperature Td and the jet static pressure pj. C was c
45、alculated as the ratio of the was calculated as the product of the jet Wh/wth. RESULTS AND DISCUSS ION The data for zero crossflow with the various hole and flow passage geometries will be presented first. one geometric configuration will be considered and used to illustrate the method for correlati
46、on of the data. Finally, the correlated data for all . geometric configurations and flow conditions investigated will be ex- amined and compared. Then, data for parallel flow with I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3663 7 Effec
47、ts of Pressure Ratio With zero crossflow. - Data presented in figure 2 show the variation in discharge coefficient with static-pressure ratio at zero crossflow for all hole and duct configurations tested. A hole having zero crossflow may be considered to represent the final air admission hole in a c
48、ombustor liner where all the air flow approaching the hole flows through the hole. These data show that the discharge coefficient at zero crossflow varies with hole and duct geometry as well as with pressure ratio. approximately 0.60 at a pressure ratio of 1.02 to approximately 0.64 at a pressure ra
49、tio of 1.30 (fig. 2). These results are comparable with those reported in reference 8 for sharp-edged orifices with normal flow. How- ever, a decrease in hole diameter or an increase in wall thickness, so that the ratio of hole diameter to wall thickness is less than approximately 6.0 (fig. 2), tends to increase the discharge coefficient. charge coefficients obtained in these c
