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3.6 Near-Field Wave Drag The near-field wave drag program computes zero-lift thickness pressure distributions for an arbitrary wing-body-nacelle configuration.The pressure distributions are integrated over the cross-sectional areas of the configuration to obtain the resultant drag force.This force may or may not correspond directly to the drag computed by the far-field method,depending upon the degree of transparency specified for the near-field pressure integrations. By transparency is meant the assumption of the far-field method that pressure fields from all components "pass through"and interact with all other components,regardless of possible physical barriers imposed by in-between components. Typical pressure data from the near-field program are presented in figure 3.6-1.A wave drag coefficient summary from the program is shown in figure 3.6-2. The near-field program has three principal uses: 1)As an analysis tool for studying the zero-lift drag forces associated with the interacting pressure fields of different configuration components.In this respect,the near-field program has an advantage over the far-field wave drag method in that there need be no assumption of transparency. 2) As a source of loads data for structural design and analysis. 3) As a source of thickness pressure fields for use in the pressure limiting options of the wing design and lift analysis programs. (This option is described in section 3.7,but basically requires that the total surface pressure coefficient on the wing,i.e.,thickness plus lift,cannot be less than some specified fraction of vacuum pressure coefficient. If the wing thickness pressures are to be used by the wing design or lift analysis programs in pressure limiting options,then the near-field program must first be run.During program execution,the thickness pressures are loaded into a system common block and are then available where needed. Nacelle pressure field options.The near-field program allows for up to 3 pairs of nacelles Tocated external to the wing-fuselage (or 2 pairs plus a single nacelle at Y=0).The nacelles may be either above or below the wing (or both). The nacelle pressure field is the pressure field imposed on the surface of the wing by the nacelles.A feature of the near-field program is the choice of 14
3.6 Near-Field Wave Drag The near-field wave drag program computes zero-lift thickness pressure distributions for an arbitrary wing-body-nacelle configuration. The pressure distributions are integrated over the cross-sectional areas of the configuration to obtain the resultant drag force. This force may or may not correspond directly to the drag computed by the far-field method, depending upon the degree of transparency specified for the near-field pressure integrations. By transparency is meant the assumption of the far-field method that pressure fields from all components "pass through" and interact with all other components, regardless of possible physical barriers imposed by in-between components. Typical pressure data from the near-field program are presented in figure 3.6-1. A wave drag coefficient summary from the program is shown in figure 3.6-2. The near-field program has three principal uses: 1) As an analysis tool for studying the zero-lift drag forces associated with the interacting pressure fields of different configuration components. In this respect, the near-field program has an advantage over the far-field wave drag method in that there need be no assumption of transparency. 2) As a source of loads data for structural design and analysis. 3) As a source of thickness pressure fields for use in the pressure limiting options of the wing design and lift analysis programs. (This option is described in section 3.7, but basically requires that the total surface pressure coefficient on the wing, i.e., thickness plus lift, cannot be less than some specified fraction of vacuum pressure coefficient.) If the wing thickness pressures are to be used by the wing design or lift analysis programs in pressure limiting options, then the near-field program must first be run. During program execution, the thickness pressures are loaded into a system common block and are then available where needed. Nacelle pressure field options. The near-field program allows for up to 3 pairs of nacelles located external to the wing-fuselage (or 2 pairs plus a single nacelle at Y=O). The nacelles may be either above or below the wing (or both). The nacelle pressure field is the pressure field imposed on the surface of the wing by the nacelles. A feature of the near-field program is the choice of 14
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.008 Wing thickness .004 引 8 l Body-on-wing interference Nacelle-on-wing interference -.004 L 0 .2 .6 1.0 Semispan fraction Wing-Body Terms CDwing =0.00639 CDwing on-body =-0.00013 interference ￡=0.00711 Cppody =0.00072 CDpodyonwing =0.00013 interference Nacelle Terms Inboard Outboard tedCwave 0.00075 0.00075 Body-on-nacelle interference 0.00002 0.00000 Nacelle-on-body interference 0.00005 0.00010 Nacelle-on-nacelle interference Direct 0.00034 0.00023 Image 0.00054 0.00046 Wing-on-nacelle interference -0.00043 -0.00058 Nacelle-on-wing interference -0.00156 ZC =0.00064 nac Wingbody-nacelle CDwave 0.00775 FIGURE 3.6-2.-TYPICAL WAVE DRAG COEFFICIENT SUMMARY- NEAR-FIELD PROGRAM (M=1.1) 16
008 c: .u_ .004 0 u "10 O u _ 0 ¢,. ._, Wing _ _ thickness .I il I Body-on-wing interference -oo4 I I I I I 0 .2 .4 .6 .B 1.0 Semispan fraction CDwing = 0.00639 CDbody = 0.0OO72 Wing-Body Terms C = -0.00013 Dwing-on-body interference CDbody_on.wing = 0.00013 interference = 0.00711 Nacelle Terms Inboard Isolated CDwav e 0.00075 Body-on-nacelle interference -0.00OO2 Nacelle-on-body interference 0.00005 Nacelle-on-nacelle interference Direct Image Wing-on-nacelle interference Nacelle-on-wing interference Outboard 0.00075 0.00000 0.00010 0.00034 0.00023 0.00054 0.00046 -0.00043 -0.00058 -0.00156 T. CDna c = 0.00064 Wing-body-nacelle CDwav e = 0.00775 FIGURE 3. 6-2.- TYPICAL WA VE DRAG COEFFICIENT SUMMA R YNEAR-FIELD PROGRAM (M = 1.1) 16