Rudy Johnson

Store Separation Trajectory Deviations Due to Unsteady Weapons Bay Aerodynamics

The combined trends toward internal carriage of weapons in modern aircraft and the design of new weapons to be neutrally stable for in creased performance have increased the probability that unsteady aerodynamics will effect store separation trajectories. Reports from time accurate computational fluid dynamics trajectory simulations have shown trajectory sensitivity to time of weapon release. Typical wind tunnel data collected to support store separation analysis cannot detect thi s effect since the data collected consists of time averaged store loads. Flight testing to inves tigate effects of bay unsteadiness has not been done since it is expensive and typically there are insufficient funds to conduct repeated store drops at identical flight conditions. Carefu lly designed and conducted small scale drop testing in wind tunnels provides a means to identif y the effect of unsteady weapons bay aerodynamics on store separation trajectories. Time accurate computational fluid dynamics trajectory analysis results on the Small Smart Bomb separating from an F-111 aircraft and a GBU-12 separation from the B-52 aircraft are reviewed. Small scale drop test data from a generic 10% scale rectangular cavity in a flatplate and from a 6% scale B-1B are introduced to provide experimental evidence of the effect of u nsteady flow on the store separation trajectory.

Multigrid approach to overset grid communication

The nonaligned multigrid method is introduced as an alternative to boundary point interpolation for communication in overset grid systems. The nonaligned multigrid method treats the individual grids as levels in a multigrid solution procedure. This technique was able to converge 69% faster than standard boundary point interpolation for Mach 2 flow over a 5-deg ramp and 28% faster for a more complex reflected shock case. For these test cases, the largest increase in convergence rate came from applying the nonaligned multigrid method to the communication between overset grids. Further coarsening of the global grid was next in effectiveness, and coarsening of local grids gave little improvement.

High Performance Computational Modeling of Unsteady Surface Loads in Complex Weapons Bays

This paper presents high performance computing results from applications of the CRAFT CFD® software to complex weapons bay configurations. Several flow control concepts have been developed based on past experience with smaller length-to-depth ratio (L/D) cavities with the intended application being a more complex and longer weapons bay. The goal in this paper is to document work done to build confidence in the modeling capability to evaluate flow control concepts for complex weapons bay configurations. The effects of some fundamental bay geometric changes are examined through Large Eddy Simulations. These simulations are validated against measurements and then used to understand the mechanisms involved. The results demonstrate that the extension of previous generic cavity modeling on shorter bays to the longer geometrically complex bay is not straightforward.

Flight-Test Experiments on Cavity Flow in an SUU-41 Pod

The conceptual development, design, ground test, and flight test of a novel weapons-cavity acoustics store separation pod led to several positive outcomes to aid in the understanding of cavity–store interaction. The weapons-cavity acoustics store separation pod was a modified SUU-41 pod (suspended utility unit) instrumented to collect forces and accelerations on a scaled model missile. In addition, time-resolved pressure and qualitative flowfield imaging were captured for the scaled cavity. This research included seven test missions on the F-16 Fighting Falcon. The flight-test data indicate that there is a clear correlation between loads and missile acceleration. The normal force, pitch moment, and acceleration data acquired for difference missile model configurations within the cavity yielded considerable insight into possible complications relating to store release. Pressure transducer data indicated the frequency of Rossiter tones and corresponded closely to results anticipated from prior flights invol...