Computational investigation of predicted store loads in mutual interference flow fields

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Steady-state numerical solutions of the Euler equations for the flow field about a wing/pylon/finned store configuration at a Mach number of 0.95 have been obtained for several store locations and attitudes. The objectives of the study were to gain insight into requirements for future computational trajectory prediction methods, to compare computationally predicted loads and pressures to measured data, and to investigate a mutual interference correction to a semi-empirical load prediction method. To meet these objectives, computational fluid dynamics (CFD) solutions were used to predict loads with the store placed at its carriage position and at 0.25, 0.50, 1 .O, and 4.0 store body diameters below the carriage position. An additional solution was obtained with the store in a position determined by a wind tunnel trajectory simulation test. Load predictions were also obtained using the Influence Function Method (IFM) for these positions. The CFD-predicted pressure distributions for the store at the carriage and trajectory positions agreed well with the measured test data, and the CFD-predicted loads on the store in these two cases agreed fairly well with the test loads. Conversely, the loads predicted by the basic IFM were in poor agreement for all cases with the measured loads and loads predicted by the CFD calculations. However, when properly applied to the IFM, the mutual interference loads correction provided a reasonable approximation to the CFD-predicted loads. Over the course of this investigation, it was found that grid density, geometric accuracy, and viscosity requirements for CFD trajectory predictions are extremely dependent on the physical properties of the store of interest, the method of release, and the portion of the trajectory over which the calculations will be performed. Nomenclature Influence coefficients used by the Influence Function Method to calculate normal and side forces. Influence coefficients used by the Influence Function Method to calculate yawingand pitching-moment coefficients. Rolling-moment coefficient, (rolling moment)/(Q*SD). Positive in the positive @ sense (see Fig. 1 ). Pitching-moment coefficient taken about the c.g., (pitching moment)/(Q*S*D). Positive in the positive 8 sense (see Fig.1). Normal-force coefficient, (normal force)/ (QnS). Positive in the positive Z direction (see Fig. 1 ). Yawing-moment coefficient taken about the c.g., (yawing moment)/(Q*S*D). Positive in the positive 6 sense (see Fig. 1). Pressure coefficient. Side force coefficient, (side force)/(Q*S). Positive in the positive Y direction (see Fig. 1). Local chord of fin on model store. Store center of gravity located 2.79 in. (model scale) axially from the store nose. Store model diameter, 1 .O .in. Distance over which the double delta correction is applied to the IFM-predicted loads, store diameters. Store model length, 5.941 in. Free-stream Mach number. Free-stream dynamic pressure, 1/2pV2. T h e research reported herem was performed by the Arnold Engineering Development Center (AEDC), A r Force Systems Command Work and analysis for thts research were done by personnel of Calspan Corportat~onJAEDC Operations, operatmg contractor for the AEDC aerospace fl~ght dynam~cs fac l~t~es Further reproduction 1s author~zed to satlsfy needs of the U S Government