Many accelerating distorted black holes

An analytical solution of four-dimensional General Relativity, representing an array of collinear and accelerating black holes, is constructed with the inverse scattering method. The metric can be completely regularised from any conical singularity, thanks to the presence of an external gravitational field. Therefore the multi-black hole configuration can be maintained at equilibrium without the need of strings or struts. Some notable subcases such as the accelerating distorted Schwarzschild black hole and the distorted double C-metric are explicitly presented. The Smarr law and the thermodynamics of these systems is studied. The Bonnor–Swaminarayan and the Bičák–Hoenselaers–Schmidt particle metrics are recovered, through appropriate limits, from the multi-black holes solutions.

Effects of Particle Size and Mainstream Inlet Angle on Deposition in a Turbine Cascade

Based on the critical velocity model, impact and capture efficiencies in an AGTB turbine cascade are investigated numerically under various inlet angles of mainstream, blowing ratios, particle sizes, and particle densities. The effect of hole configuration on deposition is analyzed based on comparisons of results from combined hole and cylindrical hole. The impact efficiency increases with the increase of particle size. Impact area on pressure side of blade surface expands with increasing of the mainstream inlet angle from 123 deg to 143 deg. The capture efficiency decreases with the increase of blowing ratio for 10 µm particles. For particles with densities of 1485 kg/m3, 1980 kg/m3, and 2475 kg/m3, the maximum capture efficiency is reached when the particle size is 5 µm. The particle capture efficiency for the combined hole is up to 3.9% lower than that for cylindrical hole when the mainstream inlet angle is 123 deg.

Optical Analysis of Hole Patterned Ag Nanoparticle Structure

A structure with periodic sub-wavelength nanohole patterns interacts with incident light and causes extraordinary optical transmission (EOT), with metal nanoparticles leading to localized surface plasmon resonance (LSPR) phenomena. To explore the effects of metal nanoparticles (NPs), optical analysis is performed for metal NP layers with periodic hole patterns. Investigation of Ag NP arrangements and comparisons with metal film structures are presented. Ag NP structures with different hole configuration are explored. Also, the effects of increasing light incident angle are investigated for metal NP structures where EOT peak at 460 nm wavelength is observed. Moreover, electric field distributions at each transmittance peak wavelengths and optical noise are analyzed. As a result, optical characteristics of metal NP structures are obtained and differences in resonance at each wavelength are highlighted.

A Numerical Study On Active Film Cooling Flow Control Through The Use Of Sister Holes

The research contained herein studied the effect of sister holes on film cooling. This novel technique surrounds a primary injection hole by two or four smaller sister holes to actively maintain flow adhesion along the surface of the blade. A numerical evaluation using the realizable κ-ε turbulence model led to the determination that the use of sister holes significantly improves adiabatic effectiveness by countering the primary vertical flow structure. Research was performed to determine the optimal hole configuration, arriving at the conclusion that placing sister holes slightly downstream of the primary injection hole improves the near-hole effectiveness, while placing sister holes slightly upstream of the primary hole improves downstream effectiveness. Similar results were found in evaluating both long and short hole geometries with a significantly less coherent flow field arising form the short hole study. However, on the whole, the sister hole approach to film cooling was found to offer viable improvements over standard cooling regimes.

A Numerical Study On Active Film Cooling Flow Control Through The Use Of Sister Holes

The research contained herein studied the effect of sister holes on film cooling. This novel technique surrounds a primary injection hole by two or four smaller sister holes to actively maintain flow adhesion along the surface of the blade. A numerical evaluation using the realizable κ-ε turbulence model led to the determination that the use of sister holes significantly improves adiabatic effectiveness by countering the primary vertical flow structure. Research was performed to determine the optimal hole configuration, arriving at the conclusion that placing sister holes slightly downstream of the primary injection hole improves the near-hole effectiveness, while placing sister holes slightly upstream of the primary hole improves downstream effectiveness. Similar results were found in evaluating both long and short hole geometries with a significantly less coherent flow field arising form the short hole study. However, on the whole, the sister hole approach to film cooling was found to offer viable improvements over standard cooling regimes.

Numerical investigation of the oil–air distribution inside ball bearings with under-race lubrication

Oil distribution inside the under-race lubricated bearing is crucial for lubrication and cooling of high-speed ball bearings. An under-race lubricated ball bearing is modeled to numerically investigate the effects of operating parameters and feed hole configuration on the distribution behavior of lubricant oil. The results of the numerical simulation indicate that the average oil volume fraction changes with a convex trend as the outer race rotating speed increases, while it changes monotonically with the inner race rotating speed, oil volume flow rate, and oil temperature. The extent of oil spreading on the outer race, cage, ball, and inner race decreases successively. Optimizing the feed hole configuration according to the average oil volume fraction is helpful to achieve precise lubrication of the under-race lubricated ball bearing.

An Experimental Study of the Leakage Flow Effect on the Film Cooling Effectiveness of a Gas Turbine Shroud

In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and this results in a locally non-uniform and high heat transfer on the surfaces. The present study experimentally investigates the effects of leakage flow through the slot between the gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment. The experiment is carried out in a linear cascade with five blades. Instead of the vane, a row of rods at the location of the vane trailing edge is installed to consider the wake effect. The leakage flow is introduced through the slot between the vane and blade rows, and additional coolant air is injected from the cooling holes installed at the vane's outer zone. The effects of the slot geometry, cooling hole configuration, and blowing ratio on the film cooling effectiveness are experimentally investigated using the pressure sensitive paint (PSP) technique. CO2 gas and a mixture of SF6 and N2 (25%+75%) are used to simulate the leakage flow to the mainstream density ratios of 1.5 and 2.0, respectively. The results indicate that the area averaged film cooling effectiveness is affected more by the slot width than by the cooling hole configuration at the same injection conditions, and the lower density ratio cases show higher film cooling effectiveness than the higher density ratio case at the same cooling configuration.

Transcranial direct current stimulation in patients after decompressive craniectomy: a finite element model to investigate factors affecting the cortical electric field

Objective To simulate the process of transcranial direct current stimulation (tDCS) on patients after decompressive craniectomy (DC), and to model cortical electric field distributions under different electrode montages, we constructed a finite element model that represented the human head at high resolution. Methods Using computed tomography images, we constructed a human head model with high geometrical similarity. The removed bone flap was simplified to be circular with a diameter of 12 cm. We then constructed finite element models according to bioelectrical parameters. Finally, we simulated tDCS on the finite element models under different electrode montages. Results Inward current had a linear relationship with peak electric field value, but almost no effect on electric field distribution. If the anode was not over the skull hole (configuration 2), there was almost no difference in electric field magnitude and focality between the circular and square electrodes. However, if the anode was right over the hole (configuration 1), the circular electrodes led to higher peak electric field values and worse focality. In addition, configuration 1 significantly decreased focality compared with configuration 2. Conclusion Our results might serve as guidelines for selecting current and electrode montage settings when performing tDCS on patients after DC.