Impingement Cooling by Multiple Asymmetric Orifice Jets

This study presents impingement cooling from a flat plate by multiple asymmetric jets. Such jets are discharged through blunt-edge inline orifice holes with a thickness-to-diameter ratio of t/Dj = 0.5 and a jet-to-jet spacing of T/Dj = 4.0, at the Reynolds number of 20,000. Firstly, fluidic features are established both in free exit and with impingement, at varying short target spacing (e.g., H/Dj = 4.0). Secondly, thermal characteristics of the jet impingement are elucidated. Results demonstrate that, due to a skewed incidence of the coolant stream upstream of concave orifice holes, the resulting multiple orifice jets are asymmetric and skewed relative to the orifice axis. These results mimic multiple fluidically inclined jets. However, asymmetric entrainment that takes place causes faster mixing with the surrounding fluid at rest as well as faster decay of momentum. This shows more effective cooling from a flat plate for the relatively short H/Dj range than conventional symmetric orifice and nozzle jets.

Accurate preparation of mesoscopic geometric characteristics of ball end milling cutter and optimization of cutting performance

According to the difficult machinability of titanium alloy, the research shows that the surface micro-textured technology can reduce the friction force and cutting temperature in the cutter-workpiece contact area. Starting with the precise preparation of micro textures by laser processing technology, this paper takes ball-end milling cutter milling titanium alloy as the research object, studies the influence of laser processing parameters on micro-textured size parameters, and optimizes the laser processing parameters as follows: laser power P = 40 W, scanning speed V = 1700 mm/s, scanning times N = 7 times, and spot diameter D = 40 μm. The distribution of temperature field and stress field during laser processing is analyzed, and the accuracy of the influence rule of laser processing parameters on micro-textured size parameters is verified, thus realizing the purpose of accurately preparing micro textures. The interactive influence of mesoscopic geometric features on the cutting performance of ball-end milling cutter is analyzed, and the genetic algorithm is used to optimize the parameters. The results show that the main factor affecting the force-heat characteristics of the tool is the blunt edge radius, and the interaction between the blunt radius of the cutting edge and the distance from blade is obvious. The optimized mesoscopic geometric parameters are as follows: the blunt edge radius is 20 μm, and the distance from blade is 110 μm, the micro-textured diameter is 30 μm, and the micro-textured spacing is 175 μm. The research content of this paper lays a foundation for efficient cutting of titanium alloy materials.

Micro Defects on Diamond Tool Cutting Edge Affecting the Ductile-Mode Machining of KDP Crystal

As a soft-brittle material, the machined surface quality of potassium dihydrogen phosphate (KDP) crystal is heavily affected by the edge quality of the diamond cutting tool. However, nanoscale micro defects inevitably occur on the freshly sharpened tool edge, and the machining mechanism for KDP crystal remains unclear. Therefore, in this work, three types of tool-edge micro defects are classified according to their cross-sections, including the blunt-edge, crescent-edge, and flat-edge micro defects. Moreover, the smoothed particle hydrodynamics (SPH) method is employed to reveal the material removal mechanism of KDP crystal with consideration of different tool-edge micro defects, and the flat-edge micro defects are subdivided into flat edge A (similar to flank wear) and flat edge B (similar to chamfered edge) on the basis of their effects in machining. The simulation results indicate that the surfaces machined by crescent edge and flat edge A are unsmooth with large-size defects due to the disappearance of hydrostatic pressure beneath the cutting edge. As for the blunt edge and flat edge B, the machined surfaces are smooth with a favorable increment of hydrostatic pressure for processing brittle materials, which indicates that a solution to eliminate the tool-edge micro defects is necessary, e.g., the passivation method. For keeping the cutting edge as sharp as possible in removing the tool-edge micro defects completely by passivation, the effect of tool shank depression angles on the geometries of the passivated cutting edge is investigated, and a high-quality cutting edge with a micro chamfered edge is obtained after passivation at a depression angle of 60° and re-sharpening of the rake face. Finally, the tool cutting performance after passivation is validated through fly-cutting experiments of KDP crystal. The chamfered edge can produce the best defect-free surface with the minimum surface roughness.

Study on Milling Temperature of Titanium Alloy with Micro-Textured Ball End Milling Cutter under Radius of Blunt Edge

A high temperature is produced in the process of precision milling of titanium alloy, and the cutting temperature can be effectively reduced by placing a micro-texture on the tool surface. In order to study the milling temperature of micro-textured ball-end milling cutter in milling titanium alloy under the combined action of a blunt radius with different edges and a micro-texture with different parameters, a new method based on micro-element theory and the generation and transmission of cutting heat has been established. At the same time, the influence of different radii of blunt edges on the milling temperature is simulated by the finite element method and experimentally verified to explore the influence of different radii of a blunt edge and micro-texture parameters on the milling temperature. Taking the milling temperature as the evaluation index, the optimum parameters of micro-circular pit texture are as follows: the diameter of micro-circular pit is 40 micron, pit spacing is 225 micron, distance from cutting edge is 100 microns, and radius of the blunt edge is 60 microns.

MICROLITHIC COMPLEX OF LATE GRAVETTIAN OF NORTHERN UKRAINE: ON THE EXAMPLE OF PUSHKARI I AND KLIUSY SITES

This article deals with new results of research microlithic complex of late Gravettian sites Pushkari I and Kliusy (Chernihiv region). The study is based on two large flint collections: Pushkari I, excavation 7 (1998—2018 by V. I. Belyaeva and P. M. Vasyliev) — 36777 units, where 4 % are tools, and 28 % of them are microlithic tools with fragments; Kliusy, excavation 1966 by I. G. Shovkoplyas — 9372 units, where 7.5 % are tools, and 35.5 % of them are microlithic tools with fragments. Microlithic complex from Pushkari I consist of 416 units — backed points (23 %), rectangles (8 %) and their fragments (64 %). Backed points represented by three main types: backed retouched 47 %, semi abrupt retouched 43 %, backed retouched with oblique retouched proximal part 10 %. It’s interesting that more of points with semi abrupt retouched have convex backed side, and backed retouched have a straight side. Rectangles also have divided at backed retouched (42 %), semi abrupt retouched (49 %) and small irregular retouched (9 %). In addition to the retouch they are different in size, semi abrupt retouched microlithics are bigger. Microlithic complex from Kliusy consist of 283 units — backed points (20 %), rectangles (10 %) and their fragments (67 %). Backed points represented by three main types: backed retouched 47 %, semi abrupt retouched 43 %, backed retouched with oblique retouched proximal part 10 %. Also, in complex submitted 4 units (7 %) of shouldered points, probably they are related to different part of the site. Rectangles have divided at backed retouched (28 %), semi abrupt retouched (48 %) and small irregular retouched (24 %). The comparative analysis of the microlithic complexes of Pushkari I and Kliusy sites lots shows, in general, typological and statistical identity. The complexes are represented by products that were used on common principles, but with slightly different shapes. The points of Pushkar I and Kliusy have one retouched long edge, with a puncturing end and a transversely truncated proximal part. At the same time retouching gives the workpiece a straight or convex blunt edge, in Pushkari I dominates — a straight line (68 %), and in Klyusy — a convex (72 %). According to the author, the shape of the blunt edge of the attachment may affect the way it is attached to the tip of the composite tool. Further studies on the study of microlithic complexes, with the involvement of modern science and technology, will provide more information on one of the main spheres of life in primitive society — hunting. Where microlithic products acted as attachments that formed the blades / blades of composite tips from organic materials.

All executives are equal, but are some more equal than others?

Purpose This paper aims to review the latest management developments across the globe and pinpoint practical implications from cutting-edge research and case studies. Design/methodology/approach This briefing is prepared by an independent writer who adds their own impartial comments and places the papers in context. Findings One of the most common, and indeed cliched, terms used in business refers to the “cutting edge”. Referring to the latest technology or innovation, it is generally accepted as being a good thing to be on the cutting edge. Firms boast about their cutting edge, organizations salute the cutting edge of their employees and governments applaud the cutting edge of their policies. Everyone wants to be on the cutting edge, and no one wants to be on whatever the opposite of the cutting edge is. Blunt edge? Reverse edge? Retreating edge? Practical Implications Provides strategic insights and practical thinking that have influenced some of the world’s leading organizations. Originality/value What is original/value of paper? This briefing saves busy executives and researchers hours of reading time by selecting only the very best, most pertinent information and presenting it in a condensed and easy-to-digest format.

Trailing-edge flow and noise control using porous treatments

This paper is concerned with the application of porous treatments as a means of flow and aerodynamic noise reduction. An extensive experimental investigation is undertaken to study the effects of flow interaction with porous media, in particular in the context of the manipulation of flow over blunt trailing edges and attenuation of vortex shedding. Comprehensive boundary layer and wake measurements have been carried out for a long flat plate with solid and porous blunt trailing edges. Unsteady velocity and surface pressure measurements have also been performed to gain an in-depth understanding of the changes to the energy–frequency content and coherence of the boundary layer and wake structures as a result of the flow interaction with a porous treatment. Results have shown that permeable treatments can effectively delay the vortex shedding and stabilize the flow over the blunt edge via mechanisms involving flow penetration into the porous medium and discharge into the near-wake region. It has also been shown that the porous treatment can effectively destroy the spanwise coherence of the boundary layer structures and suppress the velocity and pressure coherence, particularly at the vortex shedding frequency. The flow–porous scrubbing and its effects on the near-wall and large coherent structures have also been studied. The emergence of a quasi-periodic recirculating flow field inside highly permeable surface treatments has also been investigated. Finally, the paper has identified several important mechanisms concerning the application of porous treatments for aerodynamic and aeroacoustic purposes, which can help more effective and tailored designs for specific applications.

Influence of Process Parameters of 316LN Hot Wire Filling Laser Welding on the Blunt Edge Layer Forming Quality

Laser welding with hot wire addition is a new type of welding method. In order to search for appropriate laser welding technological parameters, main technological parameters have ran orthogonal optimization tests, root face layers have ran orthogonal experiments, impacts on root face forming qualities of technological parameters have been analyzed. Experimental results show that, the most influential technological parameter of weld width is welding speed, by lowering welding speed heat heat input in per unit of time will be increased, weld width decreases with the increase of defocusing amount and decrease of density of power.

Vortical Features of a Rotor Blade in Reversed Flow

The nature of the flow around a rotating blade in reverse flow is described, integrating results from fixed and rotary wing experiments. The highly 3-dimensional flow phenomena do not conform to expectations based on 2-D airfoil aerodynamics. Fixed-wing results from load measurements and flow visualization showed that the sharp-edge vortex (SEV) is a primary feature when the blade is yawed either forward or backward. The loads are better modeled using the Polhamus leading edge suction analogy. Vortex-induced pressure gradient induces an inward radial flow overcoming centrifugal effects, but away from the vortex, outward radial flow is evident everywhere. A strongly three-dimensional and attached SEV is evident under the blade at 240 degrees azimuth. This detaches and convects with the flow, remaining close to the blade by 270 degrees. The vortex seen at 300 degrees is clearly detached, but growth of the core diameter corresponding to vortex bursting, causes strong suction under the blade. The flow around the blunt edge is again strongly 3-D. Some evidence of intermittent separation is seen, but the azimuth-resolved, ensemble-averaged flow is mostly attached around the blunt edge. Preliminary static pressure contours derived from the measured 3-component velocity field are presented.