Normalized Outputs to Turbulent Boundary Layer (TBL) of Pressure and Velocity Transducers and Their Sensitivities

摘要

Two recent reports addressed the wavevector-frequency spectral density of a turbulent boundary layer (TBL) and the manner by which the filtering efficiencies of the boundaries, blankets, transducers and arrays challenge this spectral density. Whereas the goal of a design is to maintain largely intact the output to a signal (a supersonic incident pressure field), the output to a (TBL) must be largely subdued; i.e., a component in the (TBL) must be largely rejected from inducing an output in the transducer. The rejection of (TBL) that can be mustered by a flush-mounted pressure transducer and by a flush-mounted velocity transducer are compared in these reports. In this report the comparison is extended to transducer configurations that are not merely designated flush-mounted. Also, the comparison is made not just on the raw basis of the wavevector-frequency filtering efficiencies and the wavevector- frequency spectral density of (TBL), but, in addition, by evaluating the frequency spectral densities registered by the two sets of transducers. The frequency spectral densities are quantities that are more commensurate with the outputs of actual transducers and arrays. However, the evaluation of the frequency spectral densities provide for more specific assessments than those afforded by consideration of the wavevector-frequency spectral densities. In this sense, this report sacrifices generality in an attempt to render the material discussed in the two referenced reports more akin in format to the kind of information that is usually requested by designers of naval sonar systems.