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• W2100020439 abstract "This paper presents an analytical engineering level prediction method designated VTXCHN for efficient prediction of steady aerodynamic loads acting on forebodies under the influence of shed vortices. VTXCHN has been integrated hi the conceptual design aerodynamic prediction method HASC (High Angle of Attack Stability and Control), and in the comprehensive store separation analysis program STRLNCH. The forebodies may have arbitrary cross sections with or without corners or sharp chine edges. Flow conditions include subsonic flow up to the critical speed, high angle of attack, angle of side slip, and steady rotational rates. VTXCHN combines conformal transformation and elements of linear theory with models for the nonlinear effects of primary vortex shedding. The calculation procedure involves marching down the forebody from one cross section to the next, performing flow analyses in the mapped plane, and calculating aerodynamic loadings in the physical plane. Predicted results show favorable agreement with experimental longitudinal aerodynamic data for various body cross sections up to angle of attack of 50 deg at zero side slip. Lateral characteristics agree reasonably well for angles of attack up to 30 deg with up to 15 deg angle of side slip. Above 30 deg angle of attack, the side force acting 'Research Engineer, Member AIAA President, Associate Fellow AIAA 'Research Engineer Copyright ©1996 by Nielsen Engineering & Research Published by AIAA, Inc. with permission on the axisymmetric body is influenced by asymmetric vortex shedding not modeled in the present version of VTXCHN. Nomenclature Ak coefficients in confonnal numerical transformation (Eqn.l) CN, CN normal force coefficient, normal force/qJJ^ CM,Cm pitching moment coefficient, positive nose up, pitching moment/q^S,^^ Co, Cn yawing moment coefficient, positive nose to right, yawing moment/qJJ^^ Cp pressure coefficient, (p-pJ/q, CY, CY sideforce coefficient, positive to right, side fbrce/qJS^j. h body height L^ reference length, 4 in. p static pressure, Ibs/ft p, free stream static pressure, Ibs/ft q, dynamic pressure of free stream, Ibs/ft r0 equivalent radius related to confonnal transformation 8^ reference area, 12.566 in V.. free stream velocity, ft/sec x axial coordinate, positive aft Y,y lateral coordinate, positive to right Z,z vertical coordinate, positive up a angle of attack or pitch, deg p angle of sideslip, deg, positive wind from right 1 American Institute of Aeronautics and Astronautics Introduction Analysis Summary Current and future high performance flight vehicles feature a variety of forebody shapes, including chines. Flight conditions include high angles of attack and nonzero angle of side slip. Generally, under high angle of attack conditions (actually from as low as 10 deg), flow separation vortices are shed from the forebody. He vortical wake causes nonlinear aerodynamic effects on the forebody and on the downstream fuselage and lifting surface components of the aircraft It is therefore necessary to model the nonlinear effects of the forebody vortical wake in the calculation of the overall aircraft aerodynamic loadings. This kind of capability should be included in conceptual/preliminary design and analysis codes for rapid and sufficiently accurate assessment of aerodynamic characteristics of high performance aircraft. QFD codes are not yet practical enough to be incorporated in rapid turnaround conceptual/preliminary design level aerodynamic prediction codes. However, this situation may change in the near future. The engineering level methodology embodied in VTXCHN evolved from the vortex shedding modeling schemes developed by Mendenhall et al in the late 80's. Major improvements were made to the technology in the cited references resulting in the 1995 version of the VTXCHN code. The latest VTXCHN methodology presented in this paper is based on analytical engineering level models providing medium level aerodynamic fidelity. The aerodynamic loads acting on forebodies with circular and noncircular cross sections, including chine forebodies, are computed by VTXCHN under the influence of steady vortex shedding. The effects of the predicted vortical field at the end of the forebody can be included hi complete aircraft configuration aerodynamic prediction codes.li2 The methodology has been tested against experimental data for subsonic speeds. The methodology is described next. Comparisons with experimental data6 are presented for four (4) forebody shapes. Concluding remarks are given at the end of the paper. The aerodynamic analysis of a forebody by VTXCHN including effects of vortex shedding comprises conformal mapping, elements of linear and slender body theory, and nonlinear vortical modeling. The analysis proceeds from the nose to the base of the forebody. The forebody is sliced into many cross sections which are transformed to corresponding circles hi the mapped plane. As a result, an axisymmetric body is created in the mapped space. If the actual forebody is axisymmetric, this step is omitted. In either case, the axisymmetric body is modeled by point sources/sinks for linear volume effects and by two-dimensional doublets for linear upwash/sidewash effects. At the first cross section in the mapped plane, velocity components are computed at points on the body and transformed back to the physical plane. If the cross section has sharp comers or chine edges, vortices are positioned slightly off the body close to the corner or chine points hi the crossflow plane. The circumferential pressure distribution is determined in the physical plane using the compressible Bernoulli expression. For smooth cross sectional contours, the code makes use of the Stratford separation criteria applied to the pressure distribution. The locations of the shed vortices are transformed to the mapped plane. The strengths of the shed vortices are related to the imposition of a stagnation condition at the comer or chine points in the mapped plane. The vortices are then tracked aft to the next cross section hi the mapped plane. The procedure for the first cross section is repeated. The pressure distribution calculated at the second cross section in the physical plane includes nonlinear effects of the vortices shed from the first cross section. After the pressure distributions have been determined for all cross sections, the aerodynamic forces andmoments are obtained by integrating the pressures. At the end of the forebody, the vortical wake is represented by a cloud of point vortices with known strengths and positions. Further details are given below." @default.
• W2100020439 created "2016-06-24" @default.
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• W2100020439 date "1997-01-06" @default.
• W2100020439 modified "2023-09-27" @default.
• W2100020439 title "VTXCHN - Prediction method for subsonic aerodynamics and vortex formation on smooth and chined forebodies at high alpha" @default.
• W2100020439 cites W2132482424 @default.
• W2100020439 doi "https://doi.org/10.2514/6.1997-41" @default.
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