Slot Angle Research Articles

Broadband RCS reduction in microstrip patch antenna using L-shape stepped polarization rotation reflective surface

A novel L-shape stepped polarization rotation reflective surface (PRRS) for achieving broadband radar cross section (RCS) reduction of a microstrip patch antenna is proposed. The proposed PRRS consists of two scaled pairs of L-shape stepped patches and is printed on FR4 substrate backed by a metallic ground plane. The arrangement of PRRS in four orthogonal directions around the microstrip patch antenna reduces RCS in a broad frequency range of 7.07 GHz-11.06 GHz. To understand the RCS reduction throughout the entire frequency band, angled slot is introduced in the microstrip patch antenna to provide frequency shift. The microstrip patch antenna with RCS reduction is fabricated and tested. The experimental results reveal that the proposed PRRS intensely reduces the microstrip patch antenna RCS by a maximum of 35 dB with improved radiation characteristics like gain, directivity and radiation efficiency.

Design considerations for small scale rotating fluidized beds in static geometry with screens for fine particles

Design of a small scale rotating fluidized bed (RFB) with diameter of 4–6cm to fluidize 40–80μm diameter particles was investigated using computational fluid dynamics (CFD). Simulations explored the impact of the following components on pressure drop and fluidized behavior of the device: particle size, particle density, outer diameter, solids loading, height, number of inlet slots, inlet slot width, angle of inlet slots, chimney diameter, chimney number of slots, chimney slot width, chimney slot angle, and position of the chimney relative to the inlets. Fluidized behavior was evaluated based on a “fluidization quality” metric yielding information about the distribution of particles in the device. Although additional work is required to elucidate design guidelines for small scale RFBs for fine particles, the initial designs evaluated in this work indicate potential for developing a fluidized bed of relatively small diameter, presenting opportunities for process intensification for numerous potential applications.

Closed-Form Solutions Using Offset Angle for Winding Configurations of Flux-Switching Permanent Magnet Machines

This paper presents a novel perspective to understand different winding configurations of flux-switching permanent magnet (FSPM) machines. A simple analytical method is used for the calculation of total offset angle of flux linkages by taking into account an offset angle of stator slot and rotor poles. The closed-form solution is presented to find the sequence of phase windings. The 12-slot/10-pole and 12-slot/13-pole FSPM machines are conceptually segregated into two sets of 6-slot/10-pole and 6-slot/13-pole machines, respectively. This is used to address even harmonic elimination and winding configuration properties in even and odd number of rotor pole configurations. Finite element analysis and experimental results verify the concept.

Study and Analysis of Torque Handling Capacity of Slot Headed Grub Screw

A Grub screw is a type of screw generally used to lock an object within or against another object. These screws are headless and mainly used in all types of gears and shaft. The following work is based on optimization of the strength of flat slotted screw head with different slot shapes. In the paper, we have considered samples of 3 different slotted flat headed grub screw profile with their corresponding screwdriver profile. The aim was to obtain the maximum torque handling capacity among the identified slot shapes. An iterative process involving design upgradation and finite element analysis was carried out. For this purpose validation of the FEA was performed by torsion testing of the specimen in the torsion testing machine.The results showed that 17° slotted angle grub screw gives better torque handling capacity than 0° slot angle. The study shows that a variation in the slot shape of a grub screw can influence the torque handling capacity.

Effect of passive flow control on the aerodynamic performance, entropy generation and aeroacoustic noise of axial turbines for wave energy extractor

Wells turbine is the simplest type of an axial flow self-rectifying air turbine that can be used in conjunction with Oscillating Water Column (OWC) system in the extraction of ocean wave energy. It has been noticed that this turbine is subjected to early stall. As a consequence, several attempts for improving the energy extraction performance of Wells turbine within the stall regime have been investigated. One of these attempts was using an inclined slot as a passive flow control to obtain a delayed stall. In the following study, the impact of varying the angle for the slot on the performance of Wells turbine in the stall regime was investigated. Furthermore, the first law of thermodynamics and the entropy analysis has been used to examine the effect of the slot angle on the entropy generation features around the turbine blade. Moreover, Investigation of slot angle effect on the aerodynamics noise emission from Wells turbine airfoil during the normal operation and the stall regime is covered in this study. The blade of turbine with optimum angle of slot was investigated using the OWC based on actual data from the Egyptian Northern Coast. It was found that the optimum slot angle is 10° clockwise which results in 3% improvement in the torque coefficient before the stall and 15% after the stall as compared to the 0° slot. Otherwise, it gives a lower global entropy generation rate than the 0° slot by 4% before the stall and 3% after the stall. Furthermore, using airfoil of blade turbine with a slot resulted in a reduction of aeroacoustic noise by −21.2% at the stall regime under oscillating flow conditions.

Energy dissipation of slot-type flip buckets

The energy dissipation is a key index in the evaluation of energy dissipation elements. In the present work, a flip bucket with a slot, called the slot-type flip bucket, is theoretically and experimentally investigated by the method of estimating the energy dissipation. The theoretical analysis shows that, in order to have the energy dissipation, it is necessary to determine the sequent flow depth h1 and the flow speed V1 at the corresponding position through the flow depth h2 after the hydraulic jump. The relative flow depth h2 / ho is a function of the approach flow Froude number Fro, the relative slot width b/Bo, and the relative slot angle θ/β. The expression for estimating the energy dissipation is developed, and the maximum error is not larger than 9.21%.

Computational investigation of film cooling and secondary flow on turbine endwall with coolant injection from upstream interrupted slot

High pressure turbine vane surface and endwall regions are extensively cooled through discrete holes and leakage flow from combustor-turbine interface gap. For making better use of the limited amount of the leakage flow, this paper describes numerical investigation of endwall film cooling performance of a two-dimensional cascade with upstream interrupted slot injection. The geometry of the vane, size of the slot and mainstream parameters are all taken from a real engine high pressure turbine. The effects of varying blowing ratio, location of the upstream slot and coolant incidence angle on cooling effectiveness are studied. The ranges of the studied parameters are: blowing ratio 1.0, 1.7, 1.86; slot location Z/Cax = −0.1, −0.2, −0.3; coolant incidence angle −10°, 10°, 20°. The calculations are completed by solving three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence model, meanwhile, the turbulence model was validated by comparing the calculated results with the experiment data. The calculated results show an important influence of blowing ratio and axial position of the interrupted slot on film cooling effectiveness. Cooling Effectiveness is increased with increasing blowing ratio and decreasing distance between the slot and leading edge of the vane. To compare with BR = 1.7 cooling effectiveness can be improved significantly in the condition of BR = 1.86. Slot location of Z/Cax = −0.1 provides much higher cooling effectiveness than the rest two locations. The physical mechanism of the improvement is that in the condition of high blowing ratio high momentum coolant flow helps to reduce the strength of horseshoe vortex and therefore to limit its negative effect on the cooling effectiveness. The high momentum coolant jet impinges on leading edge of the vane and climbs the surface of it. The coverage of the coolant at the leading edge endwall and pressure side endwall junction becomes better. The contours of effectiveness for different slot location are similar to those of different blowing ratio. The momentum of the coolant jet increases with the slot moving close to the leading edge of the vane and creates similar effectiveness contour patterns of raising blowing ratio. The effect of varying coolant incidence angle on the cooling effectiveness is weaker than blowing ratio and slot location. Average cooling effectiveness is increased about 14% when the angle changed from 10° to 20°.

Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D

Numerical simulations of toroidal asymmetries in a tightly baffled small angle slot (SAS) divertor on the DIII-D tokamak show that toroidal asymmetries in divertor closure result in (non-axisymmetric) local onset of detachment within a density window of 10–15% on top of the nominal threshold separatrix density. The SAS divertor is explored at DIII-D for improving access to cold, dissipative/detached divertor conditions. The narrow width of the slot divertor coupled with a small magnetic field line-to-target angle facilitates the buildup of neutral density, thereby increasing radiative and neutrals-related (atoms and molecules) losses in the divertor. Small changes in the strike point location can be expected to have a large impact on divertor conditions. The combination of misaligned slot structure and non-axisymmetric perturbations to the magnetic field configuration causes the strike point to move along the divertor target plate, possibly leaving the divertor slot at some locations. The latter extreme case essentially introduces an opening in the divertor slot from where recycling neutrals can easily escape, and thereby degrade the performance of the slot divertor. Such a strike point dislocation is approximated by a finite gap in the divertor baffle for which 3D edge plasma and neutral gas simulations are performed with the EMC3-EIRENE code.

Design of compact UWB monopole planar antenna with modified partial ground plane

AbstractIn this article, an improved double‐sided printed compact UWB monopole planar radiator and a method for improving its bandwidth for ultra‐wideband application is suggested. Results show that using right angled triangular slots on the partial ground plane under the microstrip feed line (a patch radiator with a compact dimension of 14.5 × 14.75 mm2) is achieved a bandwidth of 14.3 GHz. It varies from 3.2 to 17.5 GHz for S11 < −10 dB (VSWR < 2) with center frequency of 10.35 GHz, whereas the measured bandwidth 14 GHz varies from 3.1 to 17.1 GHz. Moreover, it has a stable radiation pattern across the whole bandwidth and attains an average gain of 4.2 dBi and highest gain of 6.4 dBi at 12.5 GHz.

Effects of two-dimensional magnetic uncertainties and three-dimensional error and perturbation fields on the Small Angle Slot divertor geometry and topology

The Small Angle Slot (SAS) was recently installed on DIII-D as an advanced divertor, promising easier plasma detachment and lower temperatures across the whole target. A twofold study of the SAS magnetic geometry and topology is presented in this paper. On one hand, a two-dimensional uncertainty quantification analysis is carried out through a Monte Carlo approach in order to understand the level of accuracy of two-dimensional equilibrium computations in reconstructing the strike point and angle onto the divertor. Under typical experimental conditions, the uncertainties are found to be roughly 6.8 mm and 0.56 deg, respectively. On the other hand, a three-dimensional ‘vacuum’ analysis is carried out to understand the effects of typical external perturbation fields on the scrape-off layer topology. When the non-axisymmetric I-coils are switched on, poloidally-localized lobes are found to appear, grow, and hit the SAS target, although barely, even for 5 kA; at the same time, the strike point modulation is found to be roughly 1.8 mm and thus negligible for most purposes. Such results complement previous two-dimensional analyses in characterizing typical SAS equilibria and provide useful background information for planning and interpreting SAS experiments.

Determination of torque‐speed characteristic for a two‐speed elevator induction machine

Two-speed elevator induction machines, because of their economic usage, are still widely used in residential applications of low- and medium-height buildings. In this study, a three-stage method is presented for achieving torque-speed characteristic with an improving low-speed braking curve. In designing a procedure, firstly, a rotor aluminium alloy is changed for reaching the maximum torque at start-up. Secondly, a skew angle of rotor slots is calculated for reducing pulsating torque and smooth high-speed performance and finally, an intermediate ring rotor is proposed in order to reduce the effects of skewing leakage at a low-speed braking curve. The proposed approach for this purpose has been investigated with a finite-element method, and several prototypes have been constructed for confirmation and validation of the presented approach. The accuracy of the proposed analysis is confirmed by experimental tests and laboratory measurements are applied on all prototypes

Pin-slot clearance joints in multibody systems

The pin-slot joint is one of the most commonly used form of kinematic pairs, which with clearance will have a significant effect on the motion and dynamic response of multibody systems. In this study, the multibody system with a pin-slot clearance joint is modeled and the kinematic and dynamic effects are studied. Firstly, the generalized coordinate systems were established and the motion constraint equations of the pin-slot clearance joint were derived. Then, the theories of kinematics and dynamics were used to deduce equations of motion and dynamics. Finally, using slider-crank mechanism as the application example, the simulation study of the multibody system with a pin-slot clearance joint was carried out. The results show that there is an impact phenomenon in the moving process of the end slider, and with the increase of the slot angle, the impact phenomenon is earlier and the impact strength is weaker, however, with the increase of the slot value, the time when the impact phenomenon appearing doesn't change while the impact strength increasing. Furthermore, the maximum displacement of the end slider reduces with the increase of the slot value while the maximum value of driving torque doesn't change and the fluctuation of driving torque increased.

On the Active and Passive Flow Separation Control Techniques over Airfoils

In the present work, recent advances in the field of the active and passive flow separation control, particularly blowing and suction flow control techniques, applied on the common airfoils are briefly reviewed. This broad research area has remained the point of interest for many years as it is applicable to various applications. The suction and blowing flow control methods, among other methods, are more technically feasible and market ready techniques. It is well established that the uniform and/or oscillatory blowing and suction flow control mechanisms significantly improve the lift-to-drag ratio, and further, postpone the boundary layer separation as well as the stall. The oscillatory blowing and suction flow control, however, is more efficient compared to the uniform one. A wide range of parameters is involved in controlling the behavior of a blowing and/or suction flow control, including the location, length, and angle of the jet slots. The oscillation range of the jet slot is another substantial parameter.

Pareto optimal design of swirl cooling chambers with tangential injection using CFD, GMDH-type of ANN and NSGA-II algorithm

In this research, with regards to the considered geometrical parameters, a multi-objective optimization has been performed with the goal of achieving maximum heat transfer and minimum pressure loss in a swirl chamber. This objective has been accomplished by using the Computational Fluid Dynamics (CFD) technique, GMDH type Neural Network and the NSGA-II multi-objective optimization algorithm. The design variables include the ratio of inlet slot width to swirl chamber diameter, ratio of inlet slot height to swirl chamber diameter and the inlet slot angle. These variables are just related to geometrical parameters; and the Reynolds number, tangential jet temperature and the wall temperature are considered as constant. The objective functions include the averaged Nusselt number over swirl chamber wall and the pressure loss coefficient. CFD technique is used to analyze the flow and heat transfer and to compute the values of objective functions. The polynomials that relate the objective functions to input variables are obtained by means of GMDH algorithm. The obtained models are used to predict the values of objective functions as inputs for NSGA-II multi-objective optimization. Considering the range of changes of design variables, Pareto optimal points are obtained for the objective functions, and the Pareto points with special characteristics are introduced and discussed.

The Relationship of Throwing Arm Mechanics and Elbow Varus Torque: Within-Subject Variation for Professional Baseball Pitchers Across 82,000 Throws

Background: Likely due to the high level of strain exerted across the elbow during the throwing motion, elbow injuries are on the rise in baseball. To identify at-risk athletes and guide postinjury return-to-throw programs, a better understanding of the variables that influence elbow varus torque is desired. Purpose: To describe the within-subject relationship between elbow varus torque and arm slot and arm rotation in professional baseball pitchers. Study Design: Descriptive laboratory study. Methods: A total of 81 professional pitchers performed 82,000 throws while wearing a motusBASEBALL sensor and sleeve. These throws represented a combination of throw types, such as warm-up/catch, structured long-toss, bullpen throwing from a mound, and live game activity. Variables recorded for each throw included arm slot (angle of the forearm relative to the ground at ball release), arm speed (maximal rotational velocity of the forearm), arm rotation (maximal external rotation of the throwing arm relative to the ground), and elbow varus torque. Linear mixed-effects models and likelihood ratio tests were used to estimate the relationship between elbow varus torque and arm slot, arm speed, and arm rotation within individual pitchers. Results: All 3 metrics—arm slot (χ2 = 428, P < .001), arm speed (χ2 = 57,683, P < .001), and arm rotation (χ2 = 1392, P < .001)—were found to have a significant relationship with elbow varus torque. Within individual athletes, a 1-N.m increase in elbow varus torque was associated with a 13° decrease in arm slot, a 116 deg/s increase in arm speed, and an 8° increase in arm rotation. Conclusion: Elbow varus torque increased significantly as pitchers increased their arm rotation during the arm cocking phase, increased the rotational velocity of their arm during the arm acceleration phase of throwing, and decreased arm slot at ball release. Thus, shoulder flexibility, arm speed, and elbow varus torque (and likely injury risk) are interrelated and should be considered collectively when treating pitchers. Clinical Relevance: It is well established that elbow varus torque is related to ulnar collateral ligament injuries in overhead throwers. This study describes the relationship of arm slot, arm speed, and arm rotation to elbow varus torque in an attempt to identify modifiable risk factors for injury.

Mechanical analysis of PA66 under combined shear–compression

The large-strain mechanical behavior of PA66 was investigated using shear–compression specimens (SCS) with two opposite slots machined at different angles (15°, 30°, 45°, and 50°). Results show that strain rate and slot angle affect the equivalent stress in different levels. Slot angle sensitivity affects both flow stress and hardening characteristics, and strain rate influences elastic deformation. Increasing the strain rate gradually increases the equivalent stress. SCS with a slot angle of 30° exhibits the largest equivalent stress and the greatest effect of strain rate. The stress–strain curve differs between cylindrical specimens and SCS under quasi-static conditions. The yield stress obtained by the cylindrical specimens is higher than that of SCS. A constitutive model is modified based on the Drucker–Prager criterion to describe the effect of hydrostatic pressure and strain rate on the equivalent yield stress of polymer materials. The theoretical formula predictions are consistent with experimental results, thereby confirming the feasibility of this constitutive relationship.

Improvement of Aerodynamic Performance of Cambered Airfoils Using Leading-Edge Slots

Feasibility of increasing lift and decreasing drag by drilling narrow span-wide channels near the leading edge of NACA 4412 airfoils is investigated. It is proposed to drill two-segment slots that allow some of the incoming air to flow through them and then exit from the bottom surface of the airfoil. Such slots can result in an increased local pressure and thereby higher lift. Length, width, inlet angle, and exit angle of slots are varied to determine optimum configurations. Aerodynamic performance at different angles of attack (AoAs) and the chord-based Reynolds number of 1.6 × 106 is investigated. It is concluded that longer and narrower slots with exit streams more aligned with the air flowing below the airfoil can result in a higher lift. Also, in order to keep the slotted airfoils beneficial for AoAs greater than zero, it is proposed to (a) slightly lower the slot position with respect to the original design and (b) tilt up the first-leg by a few degrees. For the best design case considered, an average improvement of 8% is observed for lift coefficient over the entire range of AoA (with the maximum increase of 15% for AoA = 0), without any significant drag penalty.

Small angle slot divertor concept for long pulse advanced tokamaks

SOLPS-EIRENE edge code analysis shows that a gas-tight slot divertor geometry with a small-angle (glancing-incidence) target, named the small angle slot (SAS) divertor, can achieve cold, dissipative/detached divertor conditions at relatively low values of plasma density at the outside midplane separatrix. SAS exhibits the following key features: (1) strong enhancement of the buildup of neutral density in a localized region near the plasma strike point on the divertor target; (2) spreading of the cooling front across the divertor target with the slot gradually flaring out from the strike point, thus effectively reducing both heat flux and erosion on the entire divertor target surface. Such a divertor may potentially provide a power and particle handling solution for long pulse advanced tokamaks.

Simulation and Experiment of a Designed Anti-Drift Spray Nozzle

This paper reports an investigation of the relationship between spray characteristics and a nozzles’ internal structure to reveal the working mechanism of anti-drift spray nozzles. Three important structural factors were taken into account, the diameter of the inner chamber, the angle of V-shaped slot and the relative kerf depth. Three-dimensional models of the fan nozzles were set up using Solidworks software and the corresponding real nozzles were produced using high-precision 3-D printer. The flow fields inside the nozzles were simulated using the software FLUENT. By comparing the flow fields inside and outside the nozzles under the conditions of the same inner structural parameter, the relationships between spraying flow characteristics and different structural parameters was made clear, and provides a reference for optimal design of anti-drift spray nozzles.

Investigation into the effect of the angle of dual slots on an air flow field in melt blowing via numerical simulation

Abstract The effect of the angle of dual slots on an air flow field in melt blowing was researched via numerical simulation. Through establishing the geometric model of air flow field in melt blowing with dual slots, meshing, designating the boundary conditions and their parameters and numerical simulation, the result illustrates the influence of the angle of dual slots on the variations of air velocity, pressure and temperature distributions. Higher peak values of air velocity, pressure and temperature are obtained with larger angles of dual slots near the die, while only a few differences of these parameters are detected away from the die. Our results demonstrate the angle of 70° is the appropriate one that can produce the finest fibers.