Local Surface Inclination Research Articles

Aeroacoustic Loading of Impinging Supersonic Boundary-Layer Interaction on Statically Deformed Surfaces

This paper concerns the interaction of an impinging shock wave with a supersonic turbulent boundary layer over several distinct and permanently deformed surfaces, resulting in differences in the shock–boundary-layer interaction and the surface acoustic loading. High-order numerical simulations featuring two-dimensional surface deformations typically encountered in experiments are performed. The deformation amplitudes are up to half the incoming turbulent boundary-layer thickness. The results show that the high-pressure region about the shock impingement is significantly altered and can become narrower or wider depending on the local surface inclination of the deformed panel mode. The surface curvature is found to not significantly affect the separation and reattachment locations of the recirculation bubble. The power spectrum analysis of the pressure fluctuations along the panel’s midspan, where the surface attains the largest deformation amplitude, exhibits a rich and varied response. The pressure power spectrum is amplified in all of the surface deformation modes examined, with the magnitude of the amplification varying in the frequency domain, depending on the location and mode.

Efficient Aerodynamic Analysis of Air-Breathing Hypersonic Vehicle using Local Surface Inclination Method based on Unstructured Meshes

Efficient Aerodynamic Analysis of Air-Breathing Hypersonic Vehicle using Local Surface Inclination Method based on Unstructured Meshes

Development and Application of Computational Tool Using Local Surface Inclination Methods for Preliminary Analysis of Hypersonic Vehicles

This work presents a computational tool for preliminary analysis of hypersonic vehicles, based on local surface inclination methods: the HipeX. This program was developed for reading standard triangulation language (STL) geometry files and calculating pressure coefficient and temperature distributions over vehicle’s surface using the Newtonian, modified Newtonian or tangent-wedge methods. Validations were made with a cylinder and a sphere, where only the Newtonian method was applied, and with experimental data from Apollo capsule at Mach 10, where the Newtonian and the modified Newtonian methods were applied. These validations presented the code capability to read geometries as well as to estimate aerodynamic force coefficients. A preliminary application was to predict the aerodynamic force coefficients of a generic hypersonic vehicle over constant dynamic pressure trajectories of 23,940, 60,000 and 95,760 N/m2 with zero angle of attack. With a fixed dynamic pressure of 60,000 N/m2, this vehicle was tested over several Mach numbers and with angle of attack variation from -10 to 10 deg. Zero angle of attack investigation showed minor changes on the force coefficients with altitude, while the variation of angle of attack produced more pronounced variations on these parameters. Maximum flow temperatures over vehicle’s surface were estimated ranging from 850 to 5,315 K.

Interaction between surface structures and threading dislocations during epitaxial diamond growth

Threading dislocations in off‐axis grown heteroepitaxial diamond films have been visualized by preferential etching of the surface. The lateral distributions of the etch pits display characteristic inhomogeneities. Patterns with fourfold symmetry consisting of a cell structure with dislocation poor cores and dislocation rich walls aligned along [100] and [010] appear on (001) samples with off‐axis tilt toward [110]. These patterns which developed after extended growth to a thickness of 1.5 mm are mainly attributed to intrinsic anisotropies in the mutual interaction between neighboring dislocations via their stress fields. In contrast, growth on (001) surfaces with off‐axis direction toward [100] yielded patterns with twofold symmetry. Here, the etch pits are aligned exclusively along the [100] off‐axis direction which is attributed to the additional impact of the local surface inclination on the dislocations, resulting in an effective lateral movement during growth. Dislocation tilting in the local step‐flow direction away from the crystallographic [001] axis, which provides a reasonable mechanism explaining the lateral movement, is confirmed by transmission electron microscopy. Homoepitaxial growth experiments on (001) surfaces 8° off toward [100] reveal etch pit patterns around “V” shaped microstructures that suggest a similar interpretation in terms of an effective lateral movement of dislocations induced by high local surface inclination.

Three-dimensional characterization of microstructures in a SEM

A method for three-dimensional reconstruction and imaging of surface topography in a scanning electron microscope (SEM) is briefly presented. The method is based on the ‘shape from shadows’ approach and is particularly suitable for relatively smooth surfaces, where stereoscopic methods may be less efficient. The authors used a quadruple secondary electron detector system and new numerical procedures for signal processing, which quite effectively curb main errors inherent in the method. Results of experiments prove that the vertical inaccuracy of the reconstructed shape may be reduced below 10% of the view field dimensions, if local surface inclination angles are less than 65°. Thus, a SEM equipped with the system designed by the authors may serve as a tool for the inspection and measurement of geometrical issues for several classes of micro-mechanical structures.

Scanning reflection electron microscopy of surface topography by diffusely scattered electrons in the scanning electron microscope

AbstractIn this paper, the technique of scanning reflection electron microscopy (SREM) by diffusely scattered electrons in the scanning electron microscope is described in detail. A qualitative account of the formation of image contrast in SREM is also described. It is assumed that, for grazing geometry, forward‐scattered electrons reflect from regions close to the surface, following a few scattering events within the first few atomic layers, and lose very little energy in the process. The penetration depth of the primary electrons is very limited, resulting in strongly peaked envelopes of forward‐scattered electrons. It is also assumed that a surface containing topographic features presents a range of tilt angles, resulting in different reflection coefficients. Tilt contrast results because each facet has a different scattering yield, which is dependent upon local surface inclination. Full details of the instrumentation designed for SREM are described, and to illustrate the technique, results recorded from an epitaxial GaAs on GaAs crystal, Pb2(Zr,Ta)O6 thin film on silicon, and SiO2 amorphous film on silicon are presented.

Auger imaging from rough, chemically inhomogenous, materials

AbstractSurface analysis of practical materials often presents a challenging situation in Auger spectroscopy and imaging because the yield of Auger electrons depends not only on the composition of the surface but also upon the local surface inclination (the topography) and the composition of the material below the surface. The use of simultaneous imaging of the same area of a sample with an electron spectrometer and four quadrants of a backscattered electron (BSE) detector has been demonstrated previously to be very useful for the separate correction of either topographical contrast or sub‐surface composition effects. In this work the possibility is tested of using BSE detector images to correct simultaneously acquired Auger images for the presence of both topographical and sub‐surface composition effects in the same sample. Measurements on model samples with known topography and sub‐surface composition are used. The samples are formed from anisotropically etched Si(100) coated in some places with a thick Au film and then overcoated everywhere with either a thin film of CuSn alloy or partially coated with a thin film of Au. The correction process is successful in reducing the artefacts everywhere and the extent of this correction is discussed.