In an effort to reduce cost associated with flight test and certification of new weapon systems/stores for the F-22 Advanced Tactical fighter, Lockheed Martin Aeronautics has conducted a study to assess the capability of several commercial computational fluid dynamics (CFD) codes to predict cavity bay acoustics. Initially a literature survey was conducted to identify commercial, in-house, and research computer codes which have been or are presently being used to simulate cavity flows and the resultant acoustic environment. Four CFD/CAA codes were down-selected for evaluation. Code evaluations were based on comparison of predicted results with experimental data. For this purpose, four wind tunnel test cases based on the V10 1/15-scale F-22 main weapon bay (MWB) model were selected. The cases selected include both subsonic and supersonic test conditions, with both an empty MWB configuration and an inboard stowed AIM-120 configuration. This paper discusses in detail the process, application, and results using the Falcon v4 CFD code which was determined to be the best performer in predicting both subsonic and supersonic TOBSPL frequencies above 100 Hz. Results indicate Falcon v4 predictions compare very favorably for the subsonic test conditions and configurations analyzed, and tends to slightly over predict the response for the supersonic test conditions at some locations. The results of this study have proved favorable enough that correlation using a full scale CFD model with actual F-22 flight test data is proceeding.
This paper examines families of structural control systems and reveals inherent properties that provide the essential motivation behind the theory of Natural Control. It is determined that the associated fuel consumed by the controls is near minimal when the natural frequencies are identical to the controlled modal frequencies, and when the natural modes of vibration are identical to the controlled modes of vibration. Also, by casting the objective to suppress vibration in the form of an exponential stability condition, it is found that vibration is most efficiently suppressed when the modal damping rates are identical to a designer chosen decay rate. The use of a limited number of control forces over distributed control is characterized by a change in fuel consumed by the controls and by a deterioration in the dynamic performance reflected by changes in the modal damping rates. The Natural Control of a space truss demonstrates the results.
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