Effect Of Slots Research Articles

Numerical investigation of impact of fixed-exit boundary-layer bleed on supersonic intake performance

Results of numerical investigation of flow and performance characteristics of a rectangular supersonic intake with boundary-layer bleed system are presented. The effects of several flush slot bleed geometric parameters including entrance and exit area, plenum size, rear edge vertical displacement and the position relative to the incident shock have been studied to clarify their effects on the compression performance. The viscous flowfield has been obtained by solving Favre averaged Navier-Stokes equations with shear stress transport (SST) k-ω turbulence model. Moreover, the numerical methodology deployed is validated with the experimental data from literature. The analysis has been carried out in the freestream Mach number range of 1.8-2.5 and at 00 angle-of-attack, corresponding to a unit Reynolds number of approximately 1.9−2.7×107 m−1. The results show that with the use of bleed, the exit flowfield uniformity as well as the critical and peak total pressure recovery (TPR) improves considerably at all operating conditions. Furthermore, the analysis indicates that the exit throat area of a slot bleed operating at a particular design condition can be increased up to a point such that it is just sufficient to eliminate the upstream boundary-layer at its peak operation. The variation in the bleed entrance area or its position relative to the throat entrance only alters the critical performance depending on the supercritical boundary-layer mass flow loss; however, the peak TPR or the sustainable backpressure remains the same at all upstream conditions, controlled by the fixed-exit throat area. Further, it is found that for the removal of comparable amount of boundary-layer mass flow, the effects of pure flush slot or of a configuration with slight vertical displacement at its rear edge, located at the same position are similar.

Melodic-prosodic duality of the syllable

AbstractImplicit in all current theories of the syllable is some assumption of the internal configuration. Prevalent among these are the onset-rime (OR) and the moraic (μ) models, both supported by rather different types of evidence. The OR model favors an interpretation whereconstituency is exhaustive until the level of the segment which itself is a temporal unit with which melodic features associate. The μ-model distinguishes only what is non-moraic from what is moraic so that sub-syllabic constituency is an accidental result of projecting to/from the same mora. This paper postulates a more fundamentalsegment-melodycomplex that projects into two different dimensions: melody and prosody, thus capturing the insights of both the OR and μ-models through the separation of constituency issues with prosodic ones. This approach has direct applications in figuring out two long-standing conundrums in Chinese: the status of the medial glide and the prosodic properties of tonelessness. Thesegment-melodycomplex also predicts mismatches in moraicity and syllabicity as well as the mediating effect of the skeletal slots between the melodic root nodes and their moraic status.

2‐D analytical on‐load electromagnetic model for double‐layer slotted interior permanent magnet synchronous machines

A fast hybrid analytical model is presented to predict the on-load performance of double-layer interior permanent-magnet synchronous machines (IPMSMs) considering both iron bridges saturation and slotting effects. The saturation of the iron bridges is defined by a constant flux in the magnetic equivalent circuit method. The slotting effect is defined by a flux path function and virtual surface currents (VSCs) in one-dimensional (1-D) and two-dimensional (2-D) analytical methods, respectively. For the no-load condition, double-layer IPMSMs are modelled via surface-mounted permanent magnet synchronous machines with two types of the permanent magnet model and the Magnetic Islands method are used to calculate the armature reaction. The effect of the stator slots is considered by using VSCs. To increase the computation speed in the 2-D analytical method, the amount of VSC is calculated by 1-D analysis. The 1-D and 2-D analytical results for a double-layer IPMSM are compared with those of finite element analysis and experimental set-up.

Fourier-Based Modeling of an Induction Machine Considering the Finite Permeability and Nonlinear Magnetic Properties

Performance prediction of induction machines (IMs) is highly dependent on the accuracy of the material characteristics and geometry of the machine during the modeling stage. To reduce the complexity of an IM model, normally the slotting effects are neglected. Likewise, the permeability of the stator and rotor cores are assumed to be infinite leading to an ideal set of partial differential equations (PDEs) for homogenous and isotropic materials. In this paper, the permeability of the stator and rotor cores are assumed not to be infinite and the slotting effects are taken into consideration to propose a more accurate and realistic model of an IM to reduce the discrepancies between the performance expectations and actual results. Fourier-based (FB) magnetic field approach is used to fulfill this aim via anisotropic layer theory (ALT) enabling the proposed model to include distortion of magnetic flux in the slotted regions. Air-gap flux density, core losses, efficiency and torque of an IM are predicted via the FB model and are validated through the finite element analysis (FEA) and experimental studies.

Open-Circuit Air-Gap Magnetic Field Calculation of Interior Permanent Magnet Synchronous Motor With V-Shaped Segmented Skewed Poles Using Hybrid Analytical Method

Due to the local inhomogeneous magnetic saturation of the core of the interior permanent magnet synchronous motor (IPMSM), the magnetic field changes nonlinearly, which makes the analytical calculation of the magnetic field difficult. Therefore, the calculation of the magnetic field mostly relies on the finite element method (FEM). However, the high computation cost of FEM restricts the efficiency of the design and analysis of IPMSM. In this article, an analytical model (AM) of slotless open-circuit air-gap magnetic field (OC-AG-MF) of IPMSM with V-shaped segmented skewed poles is derived by combining the subdomain method (SDM) and the magnetic equivalent circuit (MEC) method, and then, the AM of slotted OC-AG-MF of IPMSM with V-shaped segmented skewed poles is obtained by introducing the complex relative permeance. To show the effectiveness of the novel AM, the OC-AG-MF and cogging torque of an IPMSM with V-shaped segmented skewed poles for electric vehicles are calculated by the AM and FEM, respectively. The spatial order, amplitude–frequency characteristics, and the 3-D spatial distribution of the OC-AG-MF are analyzed. Finally, the accuracy of the AM is experimentally verified by direct measurement of OC-AG-MF and no-load back electromotive force (EMF) of the motor. The AM proposed in this article is shown to accurately calculate the radial and tangential components of OC-AG-MF of IPMSM with V-shaped segmented skewed poles considering rotor magnetic bridge saturation effect and stator slotting effect. Meanwhile, the efficiency of the design and analysis of the motor is expected to be improved due to the reduced computational effort compared to the prevalent FEM.

Split-Flaps – a Way to Improve the Heel Stability of T-Foil Supported Craft

Abstract Horizontal T-foils allow for maximum lift generation within a given span. However, the lift force on a T-foil acts on the symmetry plane of the hull, thereby producing no righting moment. It results in a lack of transverse stability during foil-borne sailing. In this paper, we propose a system, where the height-regulating flap on the trailing edge of the foil is split into a port and a starboard part, whose deflection angles are adjusted to shift the centre of effort of the lift force. Similar to the ailerons which help in steering aircraft, the split-flaps produce an additional righting moment for stabilizing the boat. The improved stability comes, however, at a cost of additional induced resistance. To investigate the performance of the split-flap system a new Dynamic Velocity Prediction Program (DVPP) is developed. Since it is very important for the performance evaluation of the proposed system it is described in some detail in the paper. A complicated effect to model in the DVPP is the flow in the slot between the two flaps and the induced resistance due to the generated vorticity. Therefore, a detailed CFD investigation is carried out to validate a model for the resistance due to the slot effect. Two applications of the split-flap system: an Automated Heel Stability System (AHSS) and a manual offset system for performance increase are studied using a DVPP for a custom-made double-handed skiff. It is shown that the AHSS system can assist the sailors while stabilizing the boat during unsteady wind conditions. The manual offset enables the sailors to adjust the difference between the deflection angles of the two flaps while sailing, thus creating a righting moment whenever required. Such a system would be an advantage whilst sailing with a windward heel. Due to the additional righting moment from the manual offset system, the sails could be less depowered by the sailors resulting in a faster boat despite the additional induced resistance. It is shown in the paper that the control systems for the ride height and the heel stability need to be decoupled. The paper ends with a description of a mechanical system that satisfies this requirement.

Analysis of Magnetic Forces in Axial-Flux Permanent-Magnet Motors with Rotor Eccentricity

In this study, an analytical model is established to efficiently compute the magnetic field and unbalanced magnetic pull (UMP) in axial-flux permanent-magnet motors (AFPMMs). The effects of stator slotting, end effect, and rotor eccentricity on the magnetic field and forces were investigated. Static and dynamic eccentricities are analyzed and considered in the model. An effective function of the air gap permeance was introduced for effect of the stator slots to compute the flux density. A specific coefficient function is defined to calculate the end effect. A Fourier transform is used to compute the variations of the permanent-magnet remanence and the air gap permeance due to the slotted stator opposite to a slotless stator. The unbalanced magnetic forces were evaluated as a function of the air gap magnetic field using analytical equations. The proposed analytical method dramatically reduces the model size and computational time. It can be applied to the analysis of AFPMMs and is much faster than the three-dimensional finite element method (FEM). By comparing with the obtained using the FEM, the model results are validated.

Towards a better air assisted flare design for low flow conditions: Analysis of radial slot and flow effects

Numerical investigation of flow field characteristics of air injected through an inclined radial slot into a crossflowing stream has been studied for gas flaring applications. CFD is used to simulate turbulent mixing between the inclined slot jet and the crossflowing stream. The slot injection angle with respect to the crossflow, the slot jet velocity, and the slot height were varied in this study. Velocity profiles obtained from the simulations were compared to measured profiles. Simulation results showed that the centerline upflow axial velocities increased with decreasing injection angle and increasing slot height. Results also showed that decreasing injection angle increased the horizontal penetration of the jet flow into the crossflow stream.

The function of the alula with different geometric parameters on the flapping wing

Birds in nature have the ability to maintain high aerodynamic efficiency in complex flight conditions. This agility stems from the multi-degree-of-freedom flapping motion and specialized feather systems that evolved over millions of years. The leading-edge alula is considered a typical feather system that can enhance the flight envelope and capabilities of birds at low speed and high incidence. Previous studies usually adopted a static model, ignoring unsteady effects caused by flapping motion. Thus, we numerically investigated the function of the alula with different geometric parameters on the flapping wing in this paper. The alula has both the slot effect and vortex generator effect during the flapping motion, whereas the effect that plays a main role in lift enhancement changes as time varies. At the beginning of the upstroke, the slot effect plays the main role. At mid-time of the upstroke, the vortex generator effect plays the main role. Different geometric parameters have different influences on these two effects. The dimensionless spanwise location affects the strength of both the ATEV (alula trailing edge vortex) and ASV (alula streamwise vortex). The relative angle affects mainly the strength of the ATEV, whereas the deflection angle affects mainly the strength of the ASV. The optimal geometric parameters to obtain maximum lift enhancement are a dimensionless spanwise location of 0.5, a relative angle of 0°, and a deflection angle of 10°, with a lift enhancement of 5.5% compared to the baseline wing.

Robust Controller Design for Maglev Suspension Systems Based on Improved Suspension Force Model

The electromagnetic suspension-type maglev train can reach ultrahigh-speed using long stator linear synchronous motors; however, slot effect makes the motors suffer from suspension force ripple, since it causes the nonsinusoidal airgap magnetic field distribution. It has been expounded that the suspension electromagnet system is highly nonlinear and unstable in open loops. Additionally, maglev trains experience disturbances and uncertainties in service. Therefore, the robust disturbance-rejection control for electromagnet suspension system is highly necessary to maintain a constant airgap position. In this article, it is intended to propose a novel robust controller for suspension systems which ensures superior system performances despite suspension force ripple, disturbances, and uncertainties while sustaining stable suspension despite system nonlinearity. First, field harmonics are investigated along with slot effects, and an improved nonlinear mathematical model of electromagnetic force is derived. Second, the controller based on the improved force model is formulated. Then, the performance of the designed controller is evaluated on a maglev suspension system with disturbances and uncertainties. Simulation and hardware-in-the-loop experimental results demonstrate that the improved suspension force model is more accurate than the conventional models, and the corresponding controller excels in attenuating larger disturbance without sacrificing tracking performances at different speeds.

Analysis and detection of turn‐to‐turn short circuit fault in a permanent magnet Vernier generator based on modified winding function

Operation of Vernier machines is based on flux modulation. They have some advantages including maintaining the rated torque in motor applications and the rated output power in generator applications at low speeds, high torque density and relatively low torque ripple due to their magnetic gear property and fault-tolerance. In recent years, the motor with various topologies has been developed for different applications. Therefore, analysing and monitoring different faults is essential in the design and implementation stages. This study has two main purposes. First, to introduce an accurate frequency index independent of load variations for detecting the turn-to-turn short circuit (TTSC) faults in the stator windings of a permanent magnet Vernier machine. Second, modelling the machine in a healthy condition and in the presence of TTSC faults to investigate its effect on machine performance and output characteristics. An analytical model is presented using the modified winding function theory under the TTSC fault by taking into account the effect of stator slots which enhances the accuracy of the air-gap permeance function estimation. In the process of calculating the fault index, frequency components of the output characteristics of the machine are obtained from the mathematical equations of the magnetic field. It is shown that the proposed indicators are robust against load variations.

Effect of a blade end slot on supersonic compressor cascade hub-corner separation

The strong adverse pressure gradient and shock wave/boundary layer interaction that occurs in supersonic compressor cascade corner regions usually leads to large three-dimensional corner separations with extensive total pressure losses. This substantially restricts compressor load performance. In this paper, the effect of a blade end slot on corner separation caused by shock wave/boundary layer interaction was investigated. Because of the pressure difference between the pressure and suction sides, the slot enables one to induce jet flow into the endwall/blade suction-side corner region. Four different blade end slot locations are designed and their influences are investigated numerically. The mechanism of blade end slot influence on corner separation varies by position. The optimal location is slightly downstream of the initial separation point, which improves corner separation control and can reduce the cascade total pressure loss by 9.7% using the currently prescribed slot size.

Effect of a Circular Slot on Hybrid Airship Aerodynamic Characteristics

This numerical study reports the aerodynamic properties of a hybrid airship. The hybrid airships were designed by combining two semi-ellipsoids with a semi-discoid as the base model. From the base model, three different geometrics were identified to study their aerodynamic characteristics. A circular slot was provided between the pressure side and the suction side of the airship. The objective of this study was to realize the flow behavior, aerodynamic characteristics, and stability properties of such slotted hybrid flying vehicles. Interestingly, the results imply that the lift coefficient increases with an increase in the angle of attack for the slotted configurations; this is because the flow separation is delayed due to the slot opening, which in turn is due to the flow of energies from the high-pressure region to the bottom through the slots. The delayed stall angle was 50 degrees, which was 10% more than that of the base model. Aerodynamic characteristics are discussed based on surface pressure, coefficient of lift, and coefficient of drag for various slotted hybrid airships.

Performance of Permanent Magnet Synchronous Generator for Urban Water Pipeline Energy Harvester Considering Slotting and Load Effect on Radial Force Characteristic

This article proposes a 65 kW rim-driven direct-drive flux concentrated permanent magnet synchronous generator (FCPMSG) used in urban water pipeline energy harvester (UWEH) system. The proposed UWEH system plans to use hydraulic bearing; thus, a balanced radial force topology should be selected with high electromagnetic performance. Considering the hydraulic bearing mechanism and the installation of the proposed PM synchronous generator (PMSG), the effect of the loading and slot harmonics on the radial magnetic forces is analyzed. Furthermore, by studying the effect of the passive and active electric loads on the PMSGs, radial force characteristics are analyzed to select the operation region.

Corner separation control by optimizing blade end slots in a linear compressor cascade

Corner separation control is studied in this paper on a linear compressor cascade by optimizing the proposed blade end slots. In order to decrease risk of the experiment and obtain a good solution for the end slots considering finite number of calculations, a multi-parameter and multi-objective optimization of the slot to obtain the minimum total pressure loss in the cascade is carried out. Experimental investigation of the optimal slot configuration is conducted and the slot effect on the loss reduction for the compressor cascade has been validated. The slot configuration is optimized at 4° incidence angle to minimize the total pressure loss in the cascade. Measurements are also conducted at 4° incidence angle to validate the optimization procedure and CFD simulations. The layout of the end slot may not be optimal for the whole operating incidence angles for NACA65 cascade, while experiment investigations at 2° and 7° incidence angles with end slot optimized at 4° incidence angle show that total pressure loss is reduced by 5.5% and 23% respectively. The slot configuration can self-adapt the momentum of the jet flow at different incidence angles, due to the change in pressure differential between the pressure and suction surfaces. The blade end slots appear to have significant potential to decrease losses and improve compressor performance and can be applied to the real stator blade to suppress corner separation.

Effect of L-shaped slots on scour around a bridge abutment

Abstract Local scour is the most significant cause of bridge failure. Providing a short abutment with a straight slot has proved to be an effective method for reducing scour at this abutment. In this study, laboratory experiments have been conducted to investigate the effectiveness of using L-shaped slots in comparison to the commonly used straight slot, on the scour reduction at short vertical-wall abutment under clear-water flow conditions and uniform bed materials. The slots were just above the bed and their diameters equal to half the abutment's length. The results illustrated that it is essential to have a straight slot in any combination of slots, as any configuration without one is inefficient. Also, a combination of a straight slot with one side slot in the middle of the abutment's width gives better performance than an individual straight slot, as it reduces the depth, area, and volume of the scour hole by about 32.6, 26.8, and 43.6% respectively, in comparison to 23.2, 20.7, and 35.3% for the straight slot alone.

Semi-Analytical Calculation of No-Load Radial and Tangential Electromagnetic Force Waves of a Non-Salient Pole Synchronous Generator

For a marine electrical machine, its high power density and large electromagnetic (EM) load tend to bring high saturation to the magnetic circuit. When the non-linearity of ferromagnetic material is not taken into consideration, large errors will appear in the calculation of air-gap flux density and EM force wave. Considering the radial and tangential EM force waves that cause the stator core to vibrate and deform are the primary sources of EM vibration of a non-salient pole synchronous generator (NSPSG), this paper introduces a semi-analytical method of calculating the radial and tangential EM force waves, with the non-linearity of ferromagnetic material taken into account. The method includes the distributed magnetic circuit method (DMCM), the separation variable method (SVM) and the complex variable conformal transformation method (CVCTM). First of all, the radial air-gap flux density is obtained by using the DMCM to calculate the no-load magnetic circuit of the NSPSG and dealing with the non-linearity of ferromagnetic material by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B-H</i> curve. Then, the tangential air-gap flux density is calculated by the SVM and the complex relative air-gap permeance is calculated by the CVCTM to determine the effect of slotting. Finally, the radial and tangential EM force waves are obtained by Maxwell stress tensor method. The proposed semi-analytical method is verified through measuring vibration acceleration of the NSPSG.

2-D Analytical No-Load Electromagnetic Model for Slotted Interior Permanent Magnet Synchronous Machines

This paper presents a fast analytical model for estimating the components of the PM flux density distribution in the air-gap for a number of interior permanent magnet synchronous machines (IPMSMs). Deriving the two-dimensional (2-D) analytical model for IPMSMs is more challenging compared to that of surface-mounted permanent magnet synchronous machines (SPMSMs) due to the inconsistent geometry of the rotor in polar coordinates. IPMSMs are usually modeled by using 0-D or 1-D methods such as the magnetic equivalent circuit (MEC); however, the MEC method is unable to take into account the tangential component of the magnetic flux density vector. In this paper, a 2-D analytical no-load electromagnetic model for five rotor topologies of IPMSMs is proposed. The effects of the stator slots on the radial component of the PM flux density distribution in the air-gap are then included by defining an air-gap function. The effects of the stator slots on the tangential components of the PM flux density distribution in the air-gap are also considered by injecting virtual surface currents (VSCs) or virtual permanent magnets (VPMs). For verification purposes, the analytical results are compared with those of the finite element method (FEM) and the experimental results of one of the cases.

Hybrid Analytical Modeling of Air-Gap Magnetic Field in Asymmetric-Stator-Pole Flux Reversal Permanent Magnet Machine Considering Slotting Effect

This article proposes an accurate and computationally efficient hybrid analytical (HA) model for the air-gap magnetic field computation of asymmetric-stator-pole flux reversal permanent magnet machine, which can provide a thorough insight into the working mechanism by taking the slotting effects into account. The proposed HA model combines the subdomain method and Schwarz–Christoffel (SC) transformation, which can account for the stator and rotor slotting effects, respectively. The subdomain method is first employed to predict the air-gap magnetic field considering the rotor slotting effect by converting the machine geometry to a slotless stator model. Afterward, a complex relative permeance function is obtained by the SC transformation, in which the stator slotting effect is taken into account. Finally, the complete air-gap magnetic field distribution of the machine can be efficiently predicted by the proposed HA analytical model. The effectiveness of the proposed HA model is verified by both finite-element analyses and experimental results.

Design of linear phase shift transformer and analytical calculation of no-load electromagnetic field

Linear phase-shift transformer is a new type of transformer, which can be used in multi-rectifier and multi-inverter system. Taking the design of a linear phase-shifting transformer for multiple superimposed inverters as an example, a layered magnetic field analysis model of the linear phase-shifting transformer is established. Firstly, the primary side slot is treated as a smooth structure, then the model is layered and the current density of primary side is calculated by the single Fourier method Taking into account the boundary conditions of the transformer, the distribution expressions of the vector magnetic potential and the magnetic flux density in the solution region are derived, the relative permeability function of the air gap is established and the influence of the slot effect on the air gap electromagnetic field is calculated. In this paper, the distribution of electromagnetic field without load is calculated. Finally, the feasibility of the method is verified by simulation, which provides basis for the following engineering calculation and optimization design of linear transformer.