Analysis of Laminar Boundary-Layer Separation in Retarded Flow over Bodies of Revolution

Laminar boundary-layer separation phenomenon is one of the interesting and important aspects of boundary-layer flows. It occurs in various physical situations because of decreasing wall shear stress. Retarded flow velocities are one of the reasons to happen this event. Flow separation can be prevented or delayed by utilizing bodies of revolution as surface transverse curvature produces the effects of the nature of favorable pressure-gradient which in turn increases wall shear stress that keeps the flow attached to the surface. Bodies of revolution whose body contour follows power-law form also play a vital role to delay flow separation. Bodies of revolution of varying cross-sections and involving surface transverse curvature (TVC) are utilized to examine their effects on flow separation. Particularly, a convex transverse curvature has been considered due to its effects of the nature of favorable pressure-gradient which causes to delay the flow separation. A retarded flow velocity of Görtler’s type is considered in this study to investigate flow separation process. A detailed analysis is provided to understand the flow separation by calculating separation points under various assumptions. It has been observed that the body contours exponent n and the convex transverse curvature parameter k play an assistive role in the delaying of boundary-layer separation even under the influence of strong retardation. Results are presented through various Tables and graphs in order to highlight the role of the power-law exponent of external velocity m, the convex transverse curvature parameter k, and the body contours exponent n on separation points.

Improving stripping efficiency of double curvature surface on a setup with turret head

The study was performed to develop a method for selecting a rational profile of a profiled flap wheel for a turret stripping head for cleaning parts with different radius of the transverse curvature. Researchers from the Irkutsk National Research Technical University and Irkutsk Aviation Plant designed and fabricated a special PFS-4 (peen forming setup) unit to implement manufacturing technology of large-scale contour-forming components. The unit is equipped with a CNC system, two movable operating elements, a shot blaster and a turret stripping head with four flap wheels. The paper offers methods and criteria for selecting the profiled flap wheel for stripping the contour-forming surfaces of the components, depending on the curvature radius of the latter. A flap wheel with an optimal curvature radius of 40 m was chosen for analysis, which allows a sufficiently large range of profile curvature of the processed components (from 8 to 40 m) to be covered. Profiled flap wheels 100 and 200 m wide with a flap profile radius of 40 m provided uniform material removal when cleaning the surface with a curvature radius from 8 to 40 m without further overlapping with a finished strip. It was shown that wider profiled flap wheels are necessary to increase stripping efficiency. In this case, a 300 mm wide flap wheel can be used for a component surface area with a transverse curvature radius over 14 m and a 400 mm wheel for surface areas with a curvature radius of over 20 m. Thus, comparing the stripping process of a curved surface by the straight flap wheel revealed that profiled flap wheels significantly expand the workability of the PFS-4 unit turret stripping head.

A Novel Plate-Like Sensor Utilizing Curvature-Based Stiffening for Nanometrology Applications

In this study, we propose a novel plate-like sensor which utilizes curvature-based stiffening effects for enhanced nanometrology. In the proposed concept, the stiffness and natural frequencies of the sensor can be arbitrarily adjusted by applying a transverse curvature via piezoelectric actuators, thereby enabling resonance amplification over a broad range of frequencies. The concept is validated using a macroscale experiment. Then, a microscale finite element analysis is used to study the effect of applied curvature on the microplate static stiffness and natural frequencies. We show that imposed transverse curvature is an effective way to tune the in-situ static stiffness and natural frequencies of the plate sensor system. These findings will form the basis of future curvature-based stiffening microscale studies for novel scenarios in atomic force microscopy.

Properties of Twofold Tape Loops: The Influence of the Subtended Angle

Tape springs are thin-walled structures with zero longitudinal and constant transverse curvature. Folding them twice and connecting both ends creates a tape loop which acts as a linear guide. At this time, there is insufficient understanding of the influence of the tape spring's cross section on its behavior. This study investigates the influence of the subtended angle on the tape spring's behavior, especially the energy distribution and the fold radius. First, some key aspects in the design of a twofold tape loop are discussed. By performing a curvature analysis of this folded geometry, the different regions within a tape spring are identified. This information is used to identify the influence of the subtended angle on the geometry and energy state of the tape loop. The fold radius and fold angle are determined by analyzing the geometry of the fold region. The analysis showed that the energy within the transition regions cannot be neglected. The energy within these regions and the length of the transition regions both increase with the subtended angle. It is also shown that the fold radius is not constant when the subtended angle is small. The subtended angle should be above 100 deg to ensure a constant radius.