Multiple Helmholtz Resonator Heat Flux Reduction Concept

A new thermal protection concept is described and an investigation to determine its feasibility and quantify its performance is proposed. The concept involves placing an array of small cavities in the nose region of a typical hypersonic interceptor (projectile, missile, or submunition). The cavities act as multiple Helmholtz resonators, and can be made to operate in a very predictable manner to alter the inviscid strain field in the stagnation region. In effect, the resonators simulate a body with a more blunt nose geometry than actually exists. In addition, they provide "thermoacoustic" cooling from the adiabatic expansion/compression mechanism. The design is both simple and inexpensive since there is no hardware or active control device to install. The investigation is primarily experimental however a theoretical component is included to help interpret and explain the experimental results. Global surface temperature measurements will be made with an IR camera. Surface flow patterns and bow shock wave visualizations will be performed. In addition, fluctuating pressure measurements inside the cavity will be made and correlated with the global temperature and shock wave shapes. The concept also has a potential ancillary aero/optic application. Since the resonators can create a nearly planar bow shock, this effect could be useful in minimizing radial density gradients in the nose region thus reducing boresight errors for forward looking sensors.