Flight Test Reduction via Vibroacoustic Analysis

This work investigates the ability to accurately predict vibroacoustic behavior of stores under various captive carriage states and points in a typical flight envelope. Weapon fielding requires extensive flight testing, which is constrained by accurate instrumented measurement vehicles (IMV), availability of test aircraft, and competing test schedules with other weapons systems. Further, an IMV is rarely available until the design is fairly mature, leading to untimely and poorly defined environmental requirements for system design. A method typically used in free flight launch vehicles, automotive noise vibration and harshness (NVH), and in commercial subsonic flight regimes will be extended to the captive carriage conditions of stores on aircraft at varied flow speeds. Examples will be provided over a range of flight conditions and compared to IMV response data for correlation. A discussion of the theory and equations utilized in the vibroacoustic analysis will provide an explanation of the methodology used in the process. Specifics on the generation of the fluctuating surface pressures (FSP) via a specific computational fluid dynamics (CFD) solver and the formulation of the structural model representation are presented, along with approaches that were found to be most effective in accurately simulating real-world environments. Comparisons of the sound pressure level (SPL) at specific points along the vehicle are presented to demonstrate instances where the flow excitation predictions are in line with the measured microphone data, and to provide a discussion of areas that are not as close of a representation. Similarly, the acceleration responses throughout the model are provided to show examples of good response comparisons, as well as examples and discussions on other areas that did not compare as favorably to measurements made with accelerometers during the execution of the same IMV flight points. In both instances, a discussion covers factors known to provide good analytical correlation, and in cases where that was not so, known modeling approaches and features that should be included, are discussed. The results demonstrate a practical and accurate means of deriving captive carriage vibroacoustic environments that can be correlated to a reduced set of flight points, when appropriate modeling approaches are incorporated. These methods enable a reduction in the amount of flight testing that must be accomplished and pull relevant environments to the front of the product life cycle. The efficiency of solve presents a capability that easily outpaces the time to execute a typical flight campaign, at a fraction of the cost. Further, it can be conducted at any time, without the constraints of the availability of a test aircraft or an IMV.