Non-uniform slot injection into a laminar boundary layer

Summary Slot injection into a laminar boundary layer in both supersonic and subsonic flow is considered. The blowing rates are sufficiently large to provoke an interaction between the boundary layer and outer inviscid flow, and this interaction is accounted for by triple-deck theory. The non-uniform nature of the blowing velocity models the channel flow from which the injection takes place.     

Nonuniform slot injection (suction) into a compressible flow

Summary The steady nonsimilar compressible laminar boundary-layer flow over a yawed infinite circular cylinder with nonuniform slot injection (suction) has been studied up to the point of separation. The finite discontinuities arising at the leading and trailing edges of the slot for the uniform slot injection (suction) are removed by choosing appropriate nonuniform mass transfer distributions in the slot. The difficulties arising at the starting point of the streamwise co-ordinate, at the edges of the slot and at the point of separation are overcome by applying the method of quasilinear implicit finite difference scheme with an appropriate selection of finer step size along the streamwise direction. It is found that the nonuniform slot injection moves the point of separation downstream but the nonuniform slot suction has the reverse effect. The increase of Mach number shifts the point of separation upstream due to the adverse pressure gradient. The increase of total enthalpy at the wall causes the separation to occur earlier while cooling delays it. The yaw angle has very little effect on the location of the point of separation.     

Film cooling effectiveness for subsonic slot injection into a cross flow

Summary A model is developed that allows the prediction of the film cooling effectiveness produced by slot injection into a uniform cross flow. The model relies on the fact that when the slot pressure exceeds the cross flow pressure by a small amount only so that injection is weak, the resulting small parameter may be exploited to solve the flow problem. The energy equation for the flow may then be solved to determine how much protection cold gas injection gives to the wall downstream of a slot. Although the leading order energy equation must be solved numerically, a simple asymptotic expression may also be derived to allow predictions of heat transfer at large distances from the injection slot.     

Non-uniform slot injection (suction) into water boundary layer flow past yawed cylinder

The non-uniform slot injection (suction) into water boundary layer flow over a yawed infinite circular cylinder is analyzed including the temperature-dependent viscosity and Prandtl number. The difficulties arising at the starting point of the streamwise coordinate, at the edges of the slot and at the point of separation are overcome by applying the implicit finite difference scheme in combination with the quasilinearization technique. The results indicate that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but effect of non-uniform slot injection is just the opposite. Further, the effect of variable fluid properties is to move the point of separation downstream but yaw angle has very little affect on the location of the point of separation.     

Conductance of slot channels formed by cylindrical walls

Gas flow through channels formed by cylindrical walls in molecular gas flow regime is considered in this work. Ex‐ perimentally obtained conductance of three types of channels in a wide pressure range is presented. Conductance in molecular flow regime is specified. Test particle Monte Carlo (TPMC) method is used for calculation of probability of molecule transition through channels formed by cylindrical walls when wall's radii and clearances vary. Generalization of calculated values is carried out, and a uniform formula for three types of channels is given. It can be used for gas flow in vacuum systems and oil‐free pumps such as scroll pumps and Roots pumps.     

变电站直流融冰装置噪声控制

直流融冰装置作为2008年冰灾后由中国电力学院、湖南省电力设计研究院共同开发的新型装置,已广泛应用于各大型变电站,以确保电网运行的安全。但该装置的投运也在一定程度上造成了变电站环境噪声排放的超标,必须进行治理。通过介绍金华500 kV双龙变直流融冰装置的噪声治理过程,来阐明工程设计所需的原理及计算过程。     

Non-uniform slot injection (suction) or wall enthalpy into a steady nonsimilar compressible laminar boundary layer

Summary Steady two-dimensional and axisymmetric compressible nonsimilar laminar boundary-layer flows with non-uniform slot injection (or suction) and non-uniform wall enthalpy have been studied from the starting point of the streamwise co-ordinate to the exact point of separation. The effect of different free stream Mach number has also been considered. The finite discontinuities arising at the leading and trailing edges of the slot for the uniform slot injection (suction) or wall enthalpy are removed by choosing appropriate non-uniform slot injection (suction) or wall enthalpy. The difficulties arising at the starting point of the streamwise co-ordinate, at the edges of the slot and at the point of separation are overcome by applying the method of quasilinear implicit finite difference scheme with an appropriate selection of finer step size along the streamwise direction. It is observed that the non-uniform slot injection moves the point of separation downstream but the non-uniform slot suction has the reverse effect. The increase of Mach number shifts the point of separation upstream due to the adverse pressure gradient. The increase of total enthalpy at the wall causes the separation to occur earlier while cooling delays it. The non-uniform total enthalpy at the wall (i.e., the cooling or heating of the wall in a slot) along the streamwise co-ordinate has very little effect on the skin friction and thus on the point of separation.     

Flow in a rotating slot channel with injection through one wall and compensating suction through the other

The results of calculating the velocity field and integral characteristics for laminar conditions are presented and analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 4, pp. 539–543, April, 1988.     

Nonuniform multiple slot injection (suction) or wall enthalphy into a steady compressible laminar boundary layer

Summary An analysis is performed to study the effects of nonuniform multiple slot injection (suction) and nonuniform wall enthalpy on the steady nonsimilar compressible laminar boundary-layer flow over a two-dimensional and axisymmetric bodies. Nonsimilar solution is obtained from the origin of the stream-wise coordinate to the exact point of separation. The difficulties arising out at the starting point of the streamwise coordinate, at the edges of the slots and at the point of separation are overcome by applying the method of quasilinear implicit finite difference scheme with an appropriate selection of finer step sizes along the streamwise direction. It is found that the nonuniform multiple slot injection moves the point of separation downstream but the nonuniform multiple slot suction has the reverse effect. Also, separation can be delayed more effectively by applying nonuniform multiple slot injection as compared to the nonuniform single slot injection. The nonuniform total enthalpy at the wall (i.e., the cooling or heating of the wall in the slots) along the streamwise coordinate has very little effect on the skin friction and thus on the point of separation.     

The influence of slot injection/suction on the spreading of a thin film under gravity and surface tension

We consider the influence of annular slot injection/suction on the axisymmetric spreading of a thin film where gravity is the driving force. Surface tension effects are included. The singularity due to the no-slip boundary condition is overcome with a precursor film. We show how the width of the slot and magnitude of the injection/suction influences the height of ridges and depth of cavities on the profile of the free surface of the thin film. The presence of surface tension reduces the height of ridges and the depth of cavities that occur when there is no surface tension. We show that slot injection/suction causes the break up of the streamlines.     

Wideband circularly polarised slot antenna

A wideband circularly polarised slot antenna is presented. The slot antenna is fed by four microstrip line feeds orientated to have relative phases of 0deg, 90deg, 180deg and 270deg using a feed network comprising a pair of broadband 90deg hybrid. The proposed antenna delivers measured and simulated impedance bandwidths of 77.8% (1.02-2.32 GHz) and 89.1% (1.02-2.66 GHz), respectively, for standing wave ratio (SWR) < 2, measured and simulated axial-ratio bandwidths of 88.9% (1-2.6 GHz) and 81% (1.1-2.6 GHz), respectively, for axial ratio < 3 dB and measured and simulated gain bandwidths of 33% (1.5-2.1 GHz) and 27% (1.6-2.1 GHz), respectively, for gain >3 dB. A good agreement is observed between simulation and measurement.     

风电叶片防冰除冰技术的研究进展

风电作为一种清洁的可再生能源,在我国的电力结构中已经占据了重要的位置,不仅是对常规电力的补充,随着常规能源的不断消耗,风力发电将会是未来电力发展的一个趋势。然而,安装在寒冷地区或高海拔地区的风机在冬季运行时面临冰冻气候的考验。详细介绍了结冰气候及覆冰分类和叶片覆冰对风机性能的影响,并概括讨论了各种防冰除冰技术解决方案,为抗冰冻叶片的开发提供参考。     

基于Jack仿真的飞机除冰舱人机工程设计与优化

目的 改善飞机除冰舱的操作环境,提高操作员的整体舒适度和工作效率。方法 通过对飞机除冰舱作业流程的分析,确定操作员常见的操作姿态;使用Jack软件,对操作员可达域、可视域,以及舒适度进行仿真模拟分析。基于这些分析结果,对飞机除冰舱的外形以及左右扶手台等部件进行针对性的设计优化。结果 对优化设计方案分析后发现:操作员观察飞机、喷枪的视野盲区减小,常用操作手柄与开关按钮位于双手舒适可达范围内。结论 通过人机工程仿真技术可准确预判飞机除冰舱存在的人机工程设计缺陷,提高了设计合理性,为人-机-环境总体设计提供了参考。     

Polarization properties of two-dimensional slot waveguides

We propose and study slot waveguide geometries where both quasi-TE and quasi-TM modes may propagate highly confined within the same low-index slot region. Conventional horizontal and vertical slot waveguides can only provide high slot confinement for either the quasi-TM or quasi-TE modes, respectively. Different two-dimensional slot waveguide structures are analyzed in terms of their mode characteristics, such as the effective index, the confinement factor, and the overlap of quasi-TE and -TM modes within the slot. Attention is also paid to practical manufacturability. Various waveguide structures can be tailored to have zero birefringence or equal confinement at both polarizations. Values for the confinement factors and the overlap of the two polarizations, in the slot region, can reach 0.4 to 0.5.     

Controlling the polarization dependence of dual-channel directional couplers formed by silicon-on-insulator slot waveguides

The polarization dependence of directional couplers (DC) formed by silicon-on-insulator (SOI) slot waveguides was studied, and its applications as highly efficient polarization beam splitters (PBSs) and polarization-independent directional couplers (PIDCs) were investigated. The coupling lengths for the quasi-TE and quasi-TM modes may vary with the waveguide geometry due to structural birefringence; thus numerical simulations of the coupling effects in the directional couplers with different aspect ratios and waveguide spacing were conducted to obtain the optimal design parameters for high efficiency as well as compact device size. The lengths of the coupling regions of the designed PBS and PIDC are 47.61 and 23.13 μm, respectively, and they delivered good performance, with an extinction ratio greater than 20 and 1 dB bandwidth larger than 100 nm. The tolerance of fabrication error in the practical device is also discussed.     

Non-uniform slot injection (suction) into water boundary layers over (i) a cylinder and (ii) a sphere

An analysis is performed to study the effect of non-uniform slot injection (suction) into steady two-dimensional and axi-symmetric laminar boundary layers with variable viscosity and Prandtl number. Non-similar solutions have been obtained from the starting point of the streamwise co-ordinate to the exact point of separation. The difficulties arising at the starting point of the streamwise co-ordinate, at the edges of the slot and at the point of separation have been overcome by applying an implicit finite difference scheme with the quasi-linearization technique and an appropriate selection of finer step size along the streamwise direction. The results indicate that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but the effect of non-uniform slot injection is just the opposite. The heat transfer rate is found to depend strongly on viscous dissipation but the skin friction is little affected by it.     

Transverse electric modes in planar slot waveguides

Transverse electric (TE) modes in symmetrical planar slot waveguides are analytically solved, and a comprehensive knowledge about them is provided. It has been shown that there are four types of TE modes in planar slot waveguides just as the TM modes. Their field solutions, characteristic equations and cut-off conditions are derived. The cut-off conditions and the power confinement factors of the TE and TM modes are compared. It is demonstrated that there may be degeneration points between TE and TM modes. Because a three-dimensional waveguide has similar modal characteristics as its planar counterpart, our work presents a foundation of recognizing and utilizing the three-dimensional slot waveguides.     

Broadband spin-wave delay lines with slot antennas

A planar spin-wave delay line with slot antennas based on an yttrium iron garnet (YIG) film has been experimentally studied. A specific feature of the proposed device is a relatively large (about 1.8 GHz) microwave bandwidth. Within this band, the signal delay time can be smoothly controlled from 4 to 18 ns. The central frequency can be tuned by an external magnetic field within 5–9 GHz. It is demonstrated that, using slot antennas and relatively thick ferromagnetic films, it is possible to achieve a significant increase in the microwave bandwidth of spin-wave devices.     

Unsteady slot Suction from a High-Reynolds-Number Cross-Flow

The problem of unsteady suction from a high-Reynolds-number cross-flow into a slot is considered in the case where the suction is driven by a time-dependent slot pressure. The model uses linearised asymptotics based on a small parameter that defines the suction strength. An integro differential equation is derived for the mass flow into the slot and this is solved for various time-dependent slot pressures of practical interest. Closed-form expressions are also found for the shape of the shear layer dividing the external flow from the fluid in the slot. For a step function change in the slot pressure, a non-monotonic decay to the steady solution is observed, and for an oscillatory slot pressure there is a phase lag between the slot pressure and the mass flow. For rapidly changing slot pressures it is shown that slot injection can occur, even when the slot pressure remains below the free-stream pressure.