1、NASA Technical Paper 3110 September 1 991 NASA Measurements of Forces, Moments, and Pressures on a Generic Store Separating From a Box Cavity at Supersonic Speeds Rob-ert L. Stallings, Jr. Floyd J. Wilcox, Jr., and Dana K. Forrest Provided by IHSNot for ResaleNo reproduction or networking permitted
2、without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA Technical Paper 3110 National Aeronautics and Space Administration Off ice of Management Scientific and Technical Information Program Measurements of Forces, Moments, a
3、nd Pressures on a Generic Store Separating From a Box Cavity at Supersonic Speeds Robert L. Stallings, Jr. Lockheed Engineering ;ment normal-force coefficient of store, Normal force 9wA pressure coefficient, 7 store diameter, in. cavity depth or height, in. cavity length, in. store length, in. free-
4、stream Mach number local measured pressure, 1b/ft2 free-stream stagnation pressure, lb/ft2 free-stream static pressure, lb/ft2 free-stream dynamic pressure, lb/ft2 store model nose radius, in. free-stream unit Reynolds number per foot free-stream stagnation temperature, OR free-stream velocity vecto
5、r, ft/sec cavity width, in. cavity longitudinal coordinate relative to cavity front face as defined in figure 3(a), in. store longitudinal coordinate as defined in figure 4(c), in. cavity Iateral coordinate relative to cavity longitudinal centerline as defined in figure 3(a), in. cavity vertical coo
6、rdinate relative to cavity floor as defined in figure 3(b), in. vertical position of separating store relative to flat plate as shown in figure 4(b), in. e angular location on store as defined in figure 4(c), deg Abbreviations: FL cavity floor LOC location ORF orifice number RF cavity rear face ST s
7、tore SW sidewall Wind Tunnel and Test Conditions The tests were conducted in the low Mach num- ber test section of the Langley Unitary Plan Wind Tunnel (UPWT). This facility is a variable-pressure continuous-flow wind tunnel with two test sections that permit a variation in Mach number from ap- prox
8、imately 1.50 to 4.60. Ahead of each test section is an asymmetric noz- zle that permits a continuous variation in Mach num- ber from 1.50 to 2.90 in the low Mach number test section and from 2.30 to 4.60 in the high Mach num- ber test section. The test sections are approximately 7 ft long and have a
9、 square cross-sectional area of approximately 16 ft2. A complete description of the facility is given in reference 9. The store model was tested at zero angle of attack relative to the splitter plate for the free-stream test conditions shown in the following table: Models and Instrumentat ion The ve
10、rtical splitter plate used to simulate the parent body is shown in figure 1. The basic dimen- sions of the plate are shown in figure l(a), and a photograph of the installation in the low Mach num- ber test section of the Langley Unitary Plan Wind Tunnel is shown in figure l(b.) The plate was 72.8 in
11、. long and 47.3 in. wide and extended from the floor to the ceiling of the test section. To simulate internal carriage configurations, the plate assembly included a cavity that was 34 in. long, 7.5 in. wide, and 6 in. deep. Inserts were installed in the cavity to obtain a Provided by IHSNot for Resa
12、leNo reproduction or networking permitted without license from IHS-,-,-cavity length of approximately 29 in. and a width of approximately 5.7 in. Cavity depth was varied from 0 in. to 4.363 in. A boundary-layer transition strip was located 0.4 in. downstream of the flat-plate lead- ing edge. The str
13、ip consisted of No. 35 sand elements spaced 0.086 in. apart and arranged in a row parallel to the leading edge. As shown in reference 8, this size grit was effective in causing boundary-layer transi- tion to occur near the transition strip on a delta wing model for the range of test conditions of th
14、e present tests. Unpublished boundary-layer surveys from pre- vious tests using the present flat plate showed that the boundary-layer thickness at the cavity leading edge was 0.4 in. for a range of Mach number from 1.69 to 2.65. In order to maintain supersonic flow on the back side of the plate, pre
15、vious tests using this plate have shown that it is necessary to increase the back side discharge area by inclining the plate lo rel- ative to the free stream as indicated in figure l(a). Because the flow over the plate ahead of the cavity was two-dimensional and because the centerline of the store m
16、odel was always parallel to the flat-plate surface, the major effect of this lo angle was a small change in the local flow conditions on the plate. For example, at a free-stream Mach number of 2.65 and a Reynolds number of 2 x lo6, the local plate con- ditions were 2.61 and 2.044 x lo6, respectively
17、. Be- cause of this small difference, all force and moment data and pressure data were reduced based on free- stream conditions rat her than local plate conditions. Figure 1 (b) is a photograph of the store model and splitter plate assembly that includes a shallow cavity with doors attached to the s
18、ides of the cavity. Store forces and moments during separation were obtained with the store model attached to an offset sting that allowed the model to be positioned through a range of locations from inside the cavity to 13 in. away from the plate. Store pressure data were obtained on a separate mod
19、el that had the same external geometry as the force model. Shown in figure 2 are the details of the cavity. The cavity length L was 29.362 in. for all cavity depths and was obtained by installing a rear block insert in the 34.000-in. cavity as shown in figure 2. Cavity depth h was varied by using fl
20、oor supports of various heights. Cavity widths w for the two shallow cavities were the same and were approximately equal to the width of the deep cavity. The slight variation for the deep cavity was a result of using existing hardware from a previous test. Cavity doors were installed on the lateral
21、edges of the cavity for part of the test, and the spacing between the doors was equal to the cavity width. The doors had a rectangular planform and had a uniform thickness of 0.125 in. from the leading edge to the trailing edge. A total of six cavity configurations as defined in the following table
22、were tested: Shown in figure 3 are locations of the cavity pressure orifices. The number of pressure orifices ranged from 86 for the shallow cavities to 100 for the deep cavity. The locations shown in figure 3(a) are for the cavity floor, and these locations were the same for the flat plate and all
23、three cavity depths. The cavity sidewall orifice locations are shown in figure 3(b). Orifices were located at the same x-values for all three cavity depths; however, the values of z were different for all three depths. Also, there were two horizontal rows of orifices for the deep.cavities and only o
24、ne row for the shallow cavities. Orifice locations for the rear block inserts are shown in figure 3(c). Configuration 1 2 3 4 5 6 General descriptions of the force and pressure store models are given in figure 4. Both models had the same external geometry that consisted simply of an ogive nose and a
25、 cylindrical afterbody. The ogive nose was 3.668 in. long and was blunted with a nose radius of 0.032 in. The models had an overall length of 24.028 in. and were 1.200 in. in diameter. A sketch of the force model is shown in figure 4(a), and the general arrangement of the force model relative to the
26、 splitter plate is shown in figure 4(b). A sketch of the pressure model and its sting assembly is shown in figure 4(c). Pressure tubing from the model was routed through the sting to the tunnel instrumentation system. The sting assembly was offset 6.000 in. so that the model could be positioned insi
27、de as well as outside the cavity. The sting assembly for the force model had the same external geometry as the pressure model sting. The store pressure model was instrumented with 96 pressure orifices with locations as shown in figure 4(c). Measurements h 4.363 2.432 2.432 1.750 1.750 0 Aerodynamic
28、forces and moments of the store were measured with a six-component strain-gage bal- ance. Store chamber pressures were measured by means of a single static-pressure orifice located in the vicinity of the balance and were accurate to L/ h 6.731 12.073 12.073 16.778 16.778 w 5.768 5.728 5.728 5.728 5.
29、728 Doors No No Yes No Yes No Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-approximately f 3 lb/ft2. The chamber pressure measurements were used to adjust the balance mea- surements to a condition of free-stream static pres- sure over the model ba
30、se. Positive directions of the store forces and moments are shown in figure 4(b). The quoted accuracy of the strain-gage balance used is 0.5 percent of full-scale values, which are normal force, 150 lb; axial force, 30 lb; and pitching moment, 100 in-lb. Generally the repeatability of the data was b
31、etter than the quoted accuracy. Surface pressure measurements on the pressure- instrumented store and in the cavity were ob- tained using electronically scanned pressure (ESP) transducers, referenced to a vacuum. The overall accuracy of this system including calibration accu- racy is approximately f
32、 3.0 lb/ft2. Tunnel free- stream pressures were measured with precision mer- cury manometers which have an accuracy of 0.5 1b/ft2. After completion of the force and mo- ment tests and the pressure tests, a limited number of vapor-screen photographs and oil flow photographs were taken. Since the stor
33、e model and sting assembly were rolled 90“ in order to be in the proper orientation relative to the vertical splitter plate, the side force di- rection was in the tunnel vertical plane (see fig. 4(b). Therefore the tunnel flow angularity (which varied from 0.4“ at M = 1.69 to 0.8O at M = 2.00 and 2.
34、65) would be expected to primarily affect forces in the store model lateral plane rather than in the plane of the longitudinal forces as is normally the case. Lateral force and moment measurements in- dicate, however, that even in the lateral plane the effects of flow angularity were small. Because
35、these effects were small and because of the lateral symme- try of the model, the lateral force and moment data are not presented. No attempts were made to adjust the model or cavity to correct for flow angularity be- cause it varies with Mach number and because of the complexity of the complete mode
36、l assembly. Presentation of Results A complete set of pressure data is tabulated in tables I through VI and selected pressure data are presented in figure form as identified in the following list of figures. A complete set of store force and moment data is presented in figure form and is also identi
37、fied in the following list of figures. These force and moment data are not tabulated. Figures 5 and 6, which will be discussed subsequently, present previously published information on cavity flow fields; figures 7 and 8, also to be discussed subsequently, present descriptive information on the vapo
38、r-screen photographs shown in figures 9 and 10. Figure vapor-screen photographs: Cavities without doors . 9 Cavities with doors . 10 Cavity oil flow photographs: Effect of cavity flow field 11 Effect of Mach number: Zs/d = 10.83 12 Zs/d=O 13 Cavity pressure distributions: Cavities without doors . 14
39、 Summary of cavities without doors 15 Cavities with doors . 16 Summary for cavities with doors . 17 Store pressure distributions: Cavities without doors: Longitudinal distributions . 18 Summary of longitudinal distributions 19 Circumferential distributions 20 Cavities with doors: . Longitudinal dist
40、ributions 21 Summary of longitudinal distributions 22 Circumferential distributions 23 Store forces and moments: Cavities without doors: . Effect of cavity depth 24 Effect of Mach number 25 Cavities with doors: Effect of cavity depth . 26 Effect of Mach number 27 Effect of cavity doors: h = 1.750, L
41、lh = 16.778 . 28 h = 2.432, L/h = 12.073 . 29 Pressure Tables Results and Discussion A Review of Cavity Flow Fields Configuration 1 2 3 4 5 6 In general, data available in the literature show that at supersonic speeds there are two fundamen- tally different types of cavity flow fields, which have h
42、4.363 2.432 2.432 1.750 1.750 0 Llh 6.731 12.073 12.073 16.778 16.778 Doors No No Yes No Yes No Table I I1 111 IV V VI Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-been classified as open cavity and closed cavity flows. The type of flow field appe
43、ars to be primarily a func- tion of cavity length-tedepth ratio (Llh). As illus- trated in figure 5(a), for values of Llh 13 the cavity flow field is generally of the closed flow type. For this case, the shear layer expands over the cavity leading edge, impinges on the cavity floor, and exits ahead
44、of the rear face. Typical cavity floor pressure dis- tributions for this case consist of low pressures in the expansion region behind the front face followed by an increase in pressure and a pressure plateau in the impingement region. Further downstream, as the shear layer approaches the cavity rear
45、 face, the pressure levels again increase and reach a maximum value just ahead of the rear face. The local flows over the cavity front and rear faces for the closed cavity flow field are very similar to the flows over rearward- facing and forward-facing steps, respectively. Stores separating from ca
46、vities that have closed cavity flow generally experience unfavorable separation charac- teristics. At Llh % 10-13, the cavity flow field is on the verge of changing from closed cavity flow to open cavity flow (decreasing Llh) and has previously been referred to as transitional cavity flow (ref. 10).
47、 For this case, the shear layer turns through an angle to exit from the cavity coincident with impinging on the cavity floor, resulting in the impingement shock and the exit shock collapsing into a single wave. The corresponding pressure distribution shows that the extent of the plateau pressures in
48、 the impingement region has diminished and the pressure increases uni- formly from the low values in the region aft of the front face to the peak values ahead of the rear face. Unfavorable store separation characteristics are also generally associated with these types of flow fields. For Llh 8.33 th
49、e existence of these cyclic pressures are no longer ap- parent. For values of Z,/d of 8.33 and 10.83, a small pressure peak occurs on the store at x,/L, FZ 0.45 and 0.6, respectively, and is believed to be due to a weak shock wave that originates at the cavity leading edge. Store pressure distributions that are very simi- lar to the results shown in figure 18(a) for M = 1.69 are presented in figures 18(b) and 18(c) for M = 2.00 and 2.65, respectively
