Slot Gap Research Articles

Optimization of slot parameters for performance enhancement of slotted Savonius hydrokinetic turbine using Taguchi analysis

Hydrokinetic technology is an innovative approach to generate sustainable energy from river systems by using the kinetic energy of free-flowing water. To utilize such energy hydrokinetic turbines are being employed to harness the kinetic energy from flowing water. In this paper, a CFD study has been carried out to improve the efficiency of the Savonius turbine with the application of proposed slotted blades and validated with the experimental study. Also, this study aims for the optimization of a slotted blade Savonius hydrokinetic turbine (SHT) performance by examining different design parameters and their relationship using the Taguchi method. This study reveals that slot gap (y) has the greatest influence on turbine performance, followed by slot shape factor (ε), slot position (f), and tip speed ratio (λ). Moreover, the optimal combination of four parameters for maximising the efficiency of the slotted SHT is y = 1.5 mm, ε = 0.6, f = 1 % of blade diameter, and λ = 0.7 based on signal-to-noise (S/N) ratio. At this optimum combination of slotted blade profile, performance of slotted blade SHT increases by 45.19 % compared to conventional SHT. There is a slight difference of 4.16 % between experimental and computational results obtained for optimum Taguchi design.

Mechanical analysis of hybrid structured aircraft wing ribs with different geometric gaps

Abstract Wing ribs, which play a critical role in aviation, are an important design element, especially for unmanned aerial vehicles. Aircraft wing ribs are structural elements that generally extend from the wing root to the tip, used to maintain the shape of the wing, provide aerodynamic stability and add durability to the wing surface. In this study, the wing root rib of the MQ-1B Predator unmanned aerial vehicle were modeled with cavities with different geometric structures and its mechanical behavior were examined. Wing rib structures were created from circular, elliptical, slot and beam geometry gaps. The hybrid structure was created by considering the combined use of Carbon–Kevlar–Aramid. In the hybrid structure, the thickness of each fiber layer was taken into account as 0.25 mm and the wing rib consisted of six layers. The effects of different fiber angles in hybrid composite structures were also examined. As a result of the analyses, equivalent stress (von-Mises stress) and total deformation results were examined.

Large effective length and high efficiency by embedding L-shaped radiating blocks in subwavelength grating slot waveguide

Integrated optical antennas featuring large effective lengths and high radiation efficiency (RE) are essential to chip-scale light detection and ranging technology. However, there are challenges in simultaneously achieving both large effective length and high RE in silicon photonics platforms with high refractive index contrast. For traditional silicon waveguide grating antennas based on silicon photonics, the RE is relatively low and the antenna effective lengths are constrained to several hundred micrometers because of the high refractive index contrast. In this article, an embedded grating waveguide antenna which is L-shaped radiating blocks embedded in the slot gap of a silicon subwavelength grating slot waveguide is proposed and investigated numerically. Simulation results indicate the antenna’s effective length is above 4.25 mm, and the far-field divergence angle is near 0.0197°. Using L-shaped radiation blocks can break the diffraction’s perpendicular symmetry and increase the antenna’s RE to near 0.75 at 1550 nm compared to traditional design. Meanwhile, the antenna’s field-of-view reaches around 17.5° × 48.15° (θ× ϕ) to satisfy the needs of conventional optical phased arrays.

Final Examination Time Table Scheduling using Integer Programming with Average Time Slot Gap Minimization

Final Examination Time Table Scheduling using Integer Programming with Average Time Slot Gap Minimization

Experimental and numerical study on flow characteristics of dual‐cavity die based on multi‐objective optimization

AbstractSlot die coating is a common method of manufacturing electrodes for lithium‐ion batteries. In this paper, a multi‐objective optimization research on the geometry of dual‐cavity die is investigated based on the numerical simulation of lithium battery anode slurry flow combined with the surface response optimization method. First, we use the Plackett–Burman test method to screen the geometric parameters significantly affecting the optimization objective. Then, based on the Box–Behnken response surface analysis method, we determine the optimal combination of parameters. The results show that the inner cavity radius and slot gap are the main structural variables affecting exit‐velocity uniformity and die deformation. The slot gap and slot length mainly affect the inlet pressure. The coefficient of deviation of exit velocity uniformity and average inlet pressure of the optimized die structure decreased by 51.3% and 7.6%, respectively. This research provides theoretical guidance for the design of slot coating dies.Highlights Screening significant geometric parameters using Plackett–Burman test methodology. Box–Behnken response surface analysis to determine optimal parameters. Velocity uniformity and inlet pressure increased by 51.3% and 7.6%, respectively.

Turbine Blade Endwall Heat Transfer and Film Cooling Performance With Multigap Jets and Film Holes

Abstract Due to manufacturing, assembly, and operational conditions, gaps are commonly presented in the turbine components, such as platform blade-to-blade gap (slashface gap) and rim cavity platform gap (slot gap). The coolant ejected through these gaps not only limits hot mainstream gas ingestion into the disk cavity but also has the potential to provide endwall film cooling coverage. Nevertheless, the interaction of these gap flows, predesigned film hole jets, and endwall secondary flows, significantly impacts endwall heat transfer and film cooling performance and leads to a more complicated flow field near endwall. To further understand the endwall flow physics behavior in this complicated flow field, the combined effects of film hole jets and multigap leakages (slashface jet and slot jet) were experimentally studied in a transient wind tunnel with a six-blade linear cascade (nonrotating). The endwall heat transfer was measured and recorded by the IR technique at inlet average turbulence intensity (Tu) of 7.5% and an exit Mach number (Maex) of 0.4. In addition, detailed numerical predictions were also performed to discuss the flow physics near endwall and the multigap leakages behavior. Results indicated that the slashface jet is an essential contributor to endwall film cooling performance in this endwall configuration. The slashface jet delays the development of the film hole jets, leading to an enhancement of film cooling performance downstream of the film holes. Increasing the mass flow ratio of the slashface jet (MFRslashface) can prevent the high-temperature mainstream ingestion, reduce the thermal failure risks, and increase the peak of film cooling effectiveness downstream of the endwall (167% at MFRslashface = 0.5%). Due to the limitation and hindrance impacts of the disk vortex (DV), the cavity vortex (CV), and the suction side leg of the horse-shoe vortex (HV,s), the slot flow is confined to a small region downstream of the slot gap.

Low-Loss and High-Confinement Photonic Platform based on Germanium-on-Insulator at Mid-Infrared Range for Optical Sensing

We experimentally demonstrate a low-loss Ge-on-insulator (Ge-OI) passive waveguide with low absorptive yttrium oxide (Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) as an insulator for a photonic platform using a wafer-bonding technology at mid-infrared (MIR) wavelength. The lowest propagation losses of 0.84 dB/cm for a channel waveguide (ChW) and 1.79 dB/cm for a slot waveguide with a slab under the slot (s-SlW) were obtained in fundamental transverse-electric (TE) mode at 4.2 μm wavelength. We also designed additional passive circuits such as grating couplers and mode converters for the implementation of the platform. For an optical gas sensor using the platform, the narrow core width of the ChWs and nanoscale of slot gap of the s-SlWs have been derived based on the numerical design toward high optical confinement, and these were fabricated and systematically analyzed to minimize the propagation loss. From the comparison for loss measurement between a nitrogen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) ambient and a carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) containing normal atmosphere at 4.2 μm wavelength, as a consequence, narrow ChW and s-SlW showed quite high additional optical loss by the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption, revealing high potential as an optical gas sensor. In conclusion, we believe that this Ge-OI platform can be a very promising candidate for the optical sensor in terms of low-loss and high-confinement properties.

Augmented cooling performance in gas turbine blade tip with slot cooling

The blade tip is one of the most susceptible parts of gas turbine blade due to the thermally induced failure caused by a hot gas tip leakage flow through tip clearance. A highly sophisticated and efficient blade tip cooling scheme plays a crucial role in reliable operation of a gas turbine blade. In the present study, we adopted a special slot cooling scheme in turbine blade tip. The film cooling effectiveness (FCE) and flow characteristics of turbine blade tip were investigated according to the cooling flow through the slot gap in blade tip rim. A linear cascade was fabricated to measure and evaluate the cooling performance of the blade tip with the film cooling through a slotted rim versus the blade tip with cooling holes. The local FCE values of the blade tip floor and rim upper surface were measured using the pressure-sensitive paint (PSP) method. The Reynolds number based on the axial chord length and the inlet velocity in the experiment was set at 192,000. The tip clearance was varied from 1 to 3% of the blade span and the coolant mass flow rate ranged from 0.3 to 0.7% of the main flow. The slot cooling in the blade tip, which can be incorporated through an additive manufacturing, showed highly enhanced cooling performance ranging from 53 to 116% compared to that of the blade tip with film cooling holes for various tip gaps and coolant mass flow rates. The slot cooling in the blade tip is expected to improve the thermal durability and reliability of blade tip with better coolant coverage and additional convective cooling through the internal cooling passage in the narrow squealer rim.

Pressure distribution study in cone slot gap drives of electric power systems

The distribution of pressure in the conical slotted gaps of drives of electric power systems has been studied. A general expression is found to determine the pattern of pressure change along the flow of a viscous fluid in the gaps of non-contact seals, and special cases are also considered. For a narrowing gap, the maximum pressure will be in the section with the smallest gap. In this case, the plunger will tend to take a coaxial position. In the expanding gap, the maximum pressure will be in the section with a larger gap, so the plunger will be pressed against the wall of the sleeve by the forces of unbalanced pressure. With an eccentric location of the plunger in the sleeve, the pressure in the gap will change. Moreover, the uneven distribution of pressure increases as the eccentricity increases. With a larger taper of the slotted channel and with a constant inlet gap, the nature of the pressure change along the slot differs significantly from the linear one. If the flow and the plunger move in the direction of the increasing gap (expanding gap), then the plunger is pressed against the wall of the sleeve by the forces of unbalanced pressure. In this case, the contact surface of the plunger pair is destroyed, which leads to scuffing and failure of the units.

Liquid free boundary in vertical gap subject to modulated rotation

The effect of rotation velocity modulation on the equilibrium shape of the liquid-air interface in a vertical slot gap rotating around a horizontal axis is studied experimentally. The case is considered when the modulation frequency coincides with the rotation frequency. It is found that in this case, velocity modulation leads to a violation of the axial symmetry of the interface formed by the centrifugal force of inertia. The displacement of the center of symmetry of the interface increases linearly with the amplitude of the velocity modulation and decreases quadratically with the speed of rotation. It is shown that the detected phenomenon is explained by the averaged effect of an external gravitational field on a fluid in a rotating frame of reference.

Experimental study of liquids interface oscillatory dynamics in rotating slot gap

The shape of the interface between two liquids in a non-uniformly rotating slotted gap with a circular boundary is experimentally investigated. The liquids have different densities and a high viscosity contrast. We have found that the axisymmetric interface becomes unstable with an increase in the amplitude of the modulation of the rotation rate, a quasi-stationary azimuthally periodic relief excites in a threshold manner. The shape of the interface is studied by photoregistration as a function of the rotation rate, amplitude and frequency of the rotation rate modulation. The relative volume of a viscous liquid and the properties of liquids (viscosity contrast, relative density, coefficient of interfacial tension) vary. We found that the relief develops at the interface regardless of where the more viscous liquid is located, outside or inside.

Experimental Demonstration of Germanium-on-Silicon Slot Waveguides at Mid-Infrared Wavelength

We first demonstrated a slot waveguide based on a Ge-on-Si (GOS) platform with a 3 μm thickness of the Ge in the mid-infrared wavelength range at 4.2 μm. We numerically designed the slot waveguide to have a large field confinement in the slot for sensing application. Based on the design, we fabricated the GOS slot waveguide with a slot gap of 200 nm, which is coupled with in-out grating couplers. We characterized the propagation loss of the waveguides by the cut-back method and carefully compared it with channel waveguides. In fundamental TE mode, the propagation loss in the channel waveguide and the slot waveguide were quite similar (5.20 and 4.86 dB/cm, respectively), whereas the field confinement was much higher in the slot waveguides. Additionally, we simulated and analyzed the loss of the devices in terms of radiation, sidewall roughness scattering, material absorption by free-carrier absorption (FCA), and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . These results strongly suggest that the fabricated slot waveguide based on the GOS platform would be one of the promising building blocks for the optical gas sensor platform.

Probing the High-energy Gamma-Ray Emission Mechanism in the Vela Pulsar via Phase-resolved Spectral and Energy-dependent Light-curve Modeling

Abstract Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV γ-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ∼100 GeV) and the Fermi Large Area Telescope to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current-sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second γ-ray light-curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the E field, as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms.

Multi-objective optimization of a CSP-based dish Stirling field layout using Genetic Algorithm and TOPSIS method: Case studies in Ouarzazate and Madrid

CSP systems have experienced significant growth with great ability to supply clean and eco-friendly electrical power. In this paper, multi-objective optimization is carried out to design the most energy and cost-effective Solar Dish Stirling (SDS) power plant. Meteorological data from two different sites have been considered to simulate the technical and economical performances of 10 MW SDS power plant. Two main energy and economic conflicting objective functions were considered with the ultimate goal to maximize of the annual Capacity Factor and minimize the Total Cost of Site Improvements simultaneously. Several parameters such as the separation distance between collectors, ground slope, slot gap height and width have been parametrically assessed to find out effects on the Capacity Factor and the Total Cost of Site Improvements. First, a third-order multiple non-linear surrogate model was constructed. The model validity was demonstrated by the R-square values which were found to be 0.995 and 0.9964 for Ouarzazate and Madrid, respectively. Then, multi-objective optimization using Elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II) has been applied to address the trade-off between the two objective functions. The obtained Pareto Front was identified accordingly and final optimal solution was determined using Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) decision-making method. Final optimal solution corresponded to Capacity Factor (CF) values of 22.99% and 12.91% and a Total Cost of Site Improvements (TCSI) of 2.69 M$ and 2.60 M$, for Ouarzazate and Madrid, respectively.

Design of a Novel 60 GHz Millimeter Wave Q-Slot Antenna for Body-Centric Communications

The 60 GHz band is a great prospect to meet the future demand for short-range indoor communication requiring wide bandwidth and high data rates. This paper presents the design of a 60 GHz printed Q-slot patch antenna for body-centric communication. The Q-slot has a slot gap of 0.2 mm and is etched on a 6.5 mm × 11 mm rectangular patch. The slotted patch is mounted on an FR-4 (Flame Retardant) substrate that is 1.6 mm thick and has a relative permittivity of 4.3. With a partial ground plane of length of 2.2 mm, the antenna’s overall dimension is 12.9 mm × 14 mm × 1.6 mm. Computer Simulation Technology (CST) microwave studio was used to design and simulate the antenna. In free space, the antenna is resonant at 60.06 GHz with an impedance bandwidth of 12.11 GHz. At 60 GHz, the antenna’s radiation efficiency is 82.15%, with a maximum gain of 8.62 dBi. For further analysis, parametric changes were made to observe the effect on return loss, radiation efficiency, and gain. The antenna was simulated on a three-layer human torso phantom for the on-body scenario. The antenna’s resonant frequency shifted slightly to the right at 2 mm distant from the phantom while maintaining a very wide impedance bandwidth. At this point, the antenna’s radiation efficiency dropped to 56.68% and gradually increased to 74.04% at 10 mm. The maximum gain remained largely unaffected, but some grated radiation patterns were observed.

Frequency-resolved radio and high-energy emission of pulsars

Context. Pulsars are detected as broadband electromagnetic emitters from the radio wavelength up to high and very high energy in the MeV, the GeV and sometimes even in the TeV range. Multiwavelength phase-resolved spectra and light curves offer an unrivaled opportunity to understand their underlying radiation mechanisms and to localize their emission sites and therefore the particle acceleration regions. Aims. In this paper we compute pulsar multiwavelength phase-resolved light curves and spectra, assuming that both curvature and synchrotron radiation operate from inside the magnetosphere of a rotating vacuum magnet. Radio emission arises from dipolar regions above the polar caps, whereas gamma-ray energy emanates from the slot gaps in the vicinity of the separatrix between closed and open field lines. Methods. By integrating particle trajectories within the slot gaps, we compute energy-dependent photon sky maps in the radio band (MHz−GHz) and in the gamma-ray band (from MeV to GeV) for mono-energetic distribution functions of leptons. Results. We obtained many details of the energy-dependent light curves and phase-resolved spectra from the radio wavelength up to the gamma-ray energies. Choosing Lorentz factors of γ ≈ 30 for the secondary plasma responsible for the radio emitting particles and γ ≈ 107 for the primary beam producing gamma-ray-emitting particles limited by radiation reaction, we found realistic spectra that account for the wealth of multiwavelength pulsar observations.

Experimental investigation of internal leakages and effects of lubricating oil on the performance of a four-intersecting-vane rotary expander

In this paper, a four-intersecting-vane-rotary expander prototype is presented, and the performance was measured experimentally in dynamic and static conditions. The mechanism is different from conventional rotary vane machines because it has a non-circular stator with radius of between 35.7 and 40.7 mm. The prototype was designed to be eventually implemented in a refrigeration system. However, for testing compressed air was used as the working fluid. The expander was tested at rotational speeds of up to 1750 rpm, suction pressures up to 5 bar(g) and a discharge pressure of 0 bar(g). The effect of different operating parameters and lubricating oil grades on the expander was experimentally studied under dynamic conditions. Then, the internal leakage characteristics of the prototype was analyzed under static conditions. The maximum volumetric and isentropic efficiencies measured were 31.2 % and 45.6 %, respectively. Generally, higher speed and a more viscous oil improved the volumetric efficiency. The expander's isentropic efficiency was significantly affected by the suction pressure, viscosity of oil and rotational speed. The static leakage test showed that the prototype's housing was properly sealed. The average contributions of internal leakages through the radial clearance, vane tips, rotor slot and end face gaps were 37.2 %, 33.3 %, 16.2 % and 14.1 %, respectively. It was observed that the internal leakage paths were generally independent of each other.

Etched circular waveguide-based on-chip silicon mode-order converters

Mode-order converters act as the vital higher-order mode sources for on-chip multimode applications. Here, we propose a silicon-based mode-order conversion scheme by leveraging etching slots on the circular waveguide. Through designing and optimizing the etching slots and circular waveguide, the mode-order conversion from input TE0 mode to output TE1 mode has been achieved with the mode conversion efficiency of 99.1%, modal crosstalk of -25.7dB, and insertion loss of 0.21 dB, respectively, in a mode conversion size of ∼8µm×8µm (TE0-TE1). For the device fabrication, only one-step lithography and etching processes will be required, and the requirements of slot width (600 nm) and slot gap (1.49 µm) would be very beneficial for the device fabrication. Moreover, the proposed device scheme can also help achieve other higher-order mode conversions, such TE0-TE2 and TE0-TE3, where their structural parameters and performances are also analyzed. With these features of relatively good device performance, compact size, easy fabrication, and functional scalability, we believe the proposed scheme would be applied in the on-chip multimode applications to enhance their transmission capacities.

INFLUENCE OF CHANNEL GEOMETRY, PRESSURE, TEMPERATURE, OSCILLATIONS AND ADSORPTION ON OBLITERATION OF SLIT SEALS OF ELECTRIC POWER SYSTEMS

The infl uence of the geometric dimensions and confi guration of slot contactless seals on the obliteration of the gaps of plunger pairs at the design and calculation stage of drive systems of electric power systems units is considered. The combined eff ect of working fl uid contamination and the adsorption eff ect on the overgrowth of the living section of the channel was revealed. The fl ow rate during sample shedding was reduced simultaneously as a result of the channel overgrowing with contamination particles and adsorption, i.e. the formation of boundary fi lms on the channel walls. Leaks through the gap at concentric and eccentric position of the plunger in the sleeve are determined. The minimum gap is found, at which the obliteration process is stabilized and loose mud formations are washed away by the fl ow of the working fl uid. The infl uence of the pressure drop at the ends of the slot gap on the channel obliteration process was revealed. With an increase in the pressure drop, the process of stratifi cation of adsorbed layers of polar molecules accelerates, resulting in an increase in the number of contamination particles trapped in the gap per unit of time. With an increase in the temperature of the working fl uid, the process of channel obliteration accelerates, which is confi rmed by experiments. With an oscillating plunger, the fl ow through the annular gap is less than with a stationary one. This is due to the fact that the oscillating plunger occupies a position in the sleeve close to the concentric one, at which leaks are minimal. A stable fl ow rate is obtained when the working fl uid fl ows through the gaps of the plunger pairs performing reciprocating oscillating movements.

INFLUENCE OF CHANNEL GEOMETRY, PRESSURE, TEMPERATURE, OSCILLATIONS AND ADSORPTION ON OBLITERATION OF SLIT SEALS OF ELECTRIC POWER SYSTEMS

The infl uence of the geometric dimensions and confi guration of slot contactless seals on the obliteration of the gaps of plunger pairs at the design and calculation stage of drive systems of electric power systems units is considered. The combined eff ect of working fl uid contamination and the adsorption eff ect on the overgrowth of the living section of the channel was revealed. The fl ow rate during sample shedding was reduced simultaneously as a result of the channel overgrowing with contamination particles and adsorption, i.e. the formation of boundary fi lms on the channel walls. Leaks through the gap at concentric and eccentric position of the plunger in the sleeve are determined. The minimum gap is found, at which the obliteration process is stabilized and loose mud formations are washed away by the fl ow of the working fl uid. The infl uence of the pressure drop at the ends of the slot gap on the channel obliteration process was revealed. With an increase in the pressure drop, the process of stratifi cation of adsorbed layers of polar molecules accelerates, resulting in an increase in the number of contamination particles trapped in the gap per unit of time. With an increase in the temperature of the working fl uid, the process of channel obliteration accelerates, which is confi rmed by experiments. With an oscillating plunger, the fl ow through the annular gap is less than with a stationary one. This is due to the fact that the oscillating plunger occupies a position in the sleeve close to the concentric one, at which leaks are minimal. A stable fl ow rate is obtained when the working fl uid fl ows through the gaps of the plunger pairs performing reciprocating oscillating movements.