Ahmic Aerospace (United States)

Creating heat flux maps is one of the major data reduction tasks of ground-test hypersonic facilities. The ability to embed multiple high-frequency sensing elements improves the performance of Schmidt-Bolter gauges when there is significant lateral heat flux, i.e., close to the leading edge of fin elements and wings. Because the number of surface sensors is small compared to the number of basis functions necessary to resolve the spatial variation of the heat flux, the problem is ill-posed. Regularization techniques are analyzed and non-linear least squares methods are investigated. The ability of different bases to select the correct spatial distribution is investigated. New measures of the efficiency of the reconstruction when varying the number of bases are discussed. The main findings of this research are that regularization approaches perform well in resolving the depth-wise variation of the lateral component of the heat flux in embedded sensor gauges, that the generalized cross-validation technique is more accurate but less reliable than the L-curve method, and that the performance metrics of the reconstruction algorithm are mostly dependent on the symbolic evaluation of the Green's function in a novel Python hybrid approach (numerical-symbolical).

Viscous erosion is a dominate regime of surface erosion that occurs as a rocket plume impinges on the surface during a Lunar landing. It is a surface (or wall) shear driven phenomenon that is not well understood. Currently, there is no method capable of directly measuring wall shear in an actively eroding environment and to the authors' knowledge no direct measurements have even been made on static surfaces experiencing plume impingement. As a first step in pursuing this path, a series of jet impingement tests were conducted to demonstrate the performance of Ahmic's direct measurement wall shear sensors in this non-traditional boundary layer flow environment. Two surface geometries were used, a flat plate and a contoured surface which was modeled after a Lunar erosion profile. Validation of the wall shear sensors was conducted on the flat plate geometry using both CFD and multiple indirect wall shear measurement approaches. In general, most of the wall shear sensors performed well – capturing the strong radial shear gradients present in the flow and the large range of wall shear. In the central impingement region it was discovered that both the sensor internal features and sensing element size influence the quality of the measurement. Wall shear measurements over the contoured geometry were acquired and contrasted to those over the flat plate in order to understand the challenges of sensor integration and to demonstrate the first step of feasibility of acquiring direct wall shear measurements in a plume surface interaction (PSI) environment. The information gleaned from these tests will be used to design new wall shear sensors directly targeted toward PSI relevant environments.