电动汽车气流能量回收装置的设计与性能分析

为了探索电动汽车行驶气流能量回收技术以增加续航里程,借鉴小型风力发电机的研究方法,在电动汽车前舱内设计了一个由风道和升阻结合式垂直轴风力机组成的气流能量回收装置,并分析风道引起的汽车头部流场变化对整车风阻的影响.根据风能浓缩理论,考虑电动汽车前舱空间尺寸约束,设计了风道结构,通过CFX仿真验证了风道的增速作用.在CATIA中建立整车模型、带风道的整车模型、带风道和风力机的整车模型,将3个模型分别导入Ansys CFX中,研究风能回收装置对整车空气动力学性能的影响.基于相似性原理,采用放大比例的风道和风力机模型进行台架试验,得到了不同风况下的风道内流场.结果表明:风能浓缩后风速增加了约30%;采用风道和风力机的电动汽车风阻系数比原车降低8.84%;当风道与风力机处于最佳匹配位置时,风力机启动风速约为4.78 km·h^(-1),最高转速可达458 r·min^(-1).

基于抗磁悬浮的气流能量采集器

研究了一种由外壳、提升磁体、上热解石墨板、线圈、永磁体转子和下热解石墨板构成的气流能量采集器,自由悬浮于两热解石墨板之间的永磁体转子可在外界气流的作用下转动,并在线圈中产生感应电压。采用有限元软件COMSOL Multiphysics 5.3和ANSYS Maxwell 16.0建立仿真模型,对能量采集器的悬浮特性、驱动特性和输出特性进行仿真分析通过实验验证,发现当喷嘴为83°时转子所受的气流驱动力矩最大;实验测试永磁体转子悬浮高度56.5 mm,与仿真高度57.5 mm误差仅为1.77%;能量采集器稳定工作的气流量范围为137 sccm^733 sccm,最大输出电压可达160 mV。

气流能量方程及其应用

用流体运动微分方程建立能量方程,讨论绝热压缩气流能量方程及应用,并对低速气流按不可压缩流体 计算所产生的误差进行了分析。

抗磁悬浮气流能量采集器输出特性分析

对抗磁悬浮气流能量采集器的悬浮转子的悬浮特性进行分析,选定合适的悬浮间距后分析了优化前后两种不同的线圈布置方式和线圈结构参数对输出特性的影响。使用COMSOL 5.5进行有限元仿真分析,发现感应电压和平均功率随着线圈外径的增大表现出先增大后减小的特性,找到输出电压最高时线圈的布置方式及结构参数,最终确定线圈外径6 mm,导线直径0.02 mm,匝数为600匝,在2 000 r/min时采集器得到了2.33 V的峰值电压和0.32 mW的电源平均功率。

高层建筑只对着火层前室加压送风防烟漏风量的研究

本文按只对着火层前室加压送风防烟,以最不利情况下即远离加压风机端的楼层着火,在保证着火层所需基本加压送风量的前题下,对所有各层关闭风口的漏风量进行了研究。根据加压送风口的制作标准的气密性要求,即规定风口两侧静压差情况下的允许漏风量,推导出了允许的漏风面积率。然后按照流体力学理论,列出与未知数相应的气流能量方程式,用计算机联立求解这些高次方程,便得出了各层关闭风口的漏风量,据此作了进一步的分析。

Calculation on inner wall temperature in oil-gas pipe flow

Based on the energy equation of gas-liquid flow in pipeline,the explicit temperature drop formula for gas-liquid steady state calculation was derived.This formula took into consideration the Joule-Thomson effect,impact of terrain undulation and heat transfer with the surroundings along the line.Elimination of temperature iteration loop and integration of the explicit temperature equation,instead of enthalpy energy equation,into the conjugated hydraulic and thermal computation have been found to improve the efficiency of algorithm.Then,the inner wall temperature of gas-liquid flow was calculated by using explicit temperature equation and inner wall convective heat transfer coefficient of mixed flow which can be obtained by liquid convective heat transfer coefficient and gas convective heat transfer coefficient on the basis of liquid holdup.The temperature results of gas-liquid flow and inner wall in the case example presented both agree well with those in professional multiphase computational software OLGA.

Analysis of atmospheric turbulence in the upper layers of sea fog

Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. Turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.

Near ground air temperature calculation model based on heat transfer of vertical turbulent and horizontal air flow

In order to calculate the air temperature of the near surface layer in urban environment,the surface layer air was divided into several sections in the vertical direction,and some energy balance equations were developed for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was taken into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area(with a horizontal scale of less than 500 m) and a large area(with a horizontal scale of more than 1 000 m) in Guangzhou in summer were used to validate the proposed model.The calculated results accord well with the measured ones,with a maximum relative error of 4.18%.It is thus concluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.

Energy Consumption, Thermal Performance and Thermal Comfort in Public School Buildings in Jordan

Good learning outputs in schools require an acceptable physical environment inside schools. Whatever the climatic context that surrounds any school buildings, energy flows of different types should be provided. Concerns may include thermal environment, luminous environment and acoustics environment. Types of energy used are an important variable that contributes to thermal comfort. Physical structure of the school building is another factor to be taken into consideration. This article established a relationship between thermal comfort inside schools and types of energy flows which have been consumed to maintain the level of comfort required, controlled by the building fabric and consequent economic factors that affect energy consumption of school buildings. Different approaches were applied in order to achieve the research objectives. Field surveys, field measurements and analyzing historical data were the most approaches followed to implement this study. The final outputs of this work have a national value nationwide： establishing a relationship among thermal comfort, energy flows and building fabric is of importance. Furthermore, it is of great importance to the decision maker for educational facilities. Research will also establish a wide platform based on scientific investigations for developing climate responsive school architecture in Jordan.

Temperature-flow regulation rule in indirect connection heating system and its energy-saving contrast analysis

Primary and secondary networks are treated as a whole in indirect heating systems, and an advanced new temperature-flow regulation method is presented whose flow ratio is greater than 60% in a secondary network and 30% in a primary network when under a partial load. Through deducing and optimizing an exponential function flow regulation rule, the formulae of flow regulation and the supply and return water temperatures are obtained, and their relevant curves are plotted. After comparison, it is found that this control method has a huge energy conservation space, and it should therefore be generalized soon.

2019年北京高考物理24题引发的思考

针对最近热议的2019年北京高考物理24题中雨滴在空气中下落所受阻力的形式及导出其的模型,本文从实际情境中雨滴的收尾速度出发进行了讨论.计算发现,雨滴在空气中所受阻力主要是压差阻力,与下落速度二次方成正比.高考标准答案给出的结果与此符合.同时,本文还分析了碰撞模型在低速范围内所得出阻力与速度一次方成正比的结果失效的原因.

Sensitivity experiments of impacts of large-scale urbanization in East China on East Asian winter monsoon

By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.

Effects of Measuring Positions on the Measured Aerodynamic Performance of a Centrifugal Compressor

This paper performs a numerical simulation of three-dimensional flow field in a centrifugal compressor with long inlet and outlet pipes using CFX software.By arranging virtual probes at different positions in both inlet and outlet planes,the aerodynamic performance of the centrifugal compressor is measured and compared with each other.Then effects of measuring positions on measurement results are discussed.The results show that it will generate notable measuring errors of the pressure ratio and efficiency if the inlet total pressure is measured using a single-point probe.The inlet total pressure data can be accurate when they are measured using a 3-point rake.The outlet total pressure and total temperature data can not be accurate if they are respectively measured at one circumferential position even using a multi-point rake.Increasing tangential measuring positions at the outlet is effective to improve the test accuracy.When the outlet total pressure and total temperature are respectively measured at 3 tangential positions,the data can be almost accurate.

Effect of Diffuser Vane Shape on the Performance of a Centrifugal Compressor Stage

The present paper reports the results of experimental investigations on the effect of diffuser vane shape on the performance of a centrifugal compressor stage. These studies were conducted on the chosen stage having a back- ward curved impeller of 500 turn tip diameter and 24.5 mm width and its design flow coefficient is Фd=0.0535. Three different low solidity diffuser vane shapes namely uncarnbered aerofoil, constant thickness flat plate and circular arc cambered constant thickness plate were chosen as the variants for diffuser vane shape and all the three shapes have the same thickness to chord ratio （t/c=0.1）. Flow coefficient, polytropic efficiency, total head coeffi- cient, power coefficient and static pressure recovery coefficient were chosen as the parameters for evaluating the effect of diffuser vane shape on the stage performance. The results show that there is reasonable improvement in stage efficiency and total head coefficient with the use of the chosen diffuser vane shapes as compared to conven- tional vaneless diffuser. It is also noticed that the aero foil shaped LSD has shown better performance when com- pared to flat plate and circular arc profiles. The aerofoil vane shape of the diffuser blade is seen to be tolerant over a considerable range of incidence.

Energy convergence effect and jet phenomenon of shock-heavy spherical bubble interaction

We present computational results on the evolution of the shock-accelerated heavy bubbles surrounded by nitrogen with the Atwood number At = 0.497–0.677 and the emphasis is on the jet phenomenon caused by the shock focusing. The multi-fluid Eulerian equation is solved by a finite volume method based on MUSCL-Hancock approach. Based on the numerical schlieren and the distributions of density and pressure, it is found that there are three typical jet structures(outward jet, no jet, inward jet) for different combinations of gas mixture inside the bubble which determine the position of shock focusing relative to the downstream pole of the heavy bubble(upstream of the pole, at the pole, downstream the pole). Compared with the inward jet, the velocity of outward jet is obviously larger. As At increases, the moment of jet formation is postponed, and the maximal values and magnifications of pressure and density increase distinctly. Therefore, the energy convergence effects are heavily enhanced with the increase of bubble gas density.

Heat Transfer and Aerodynamics of Complex Shroud Leakage Flows in a Low-Pressure Turbine

A numerical investigation on over-shroud & inter-shroud leakage flow has been carried out to explore the underneath flow physics at the stage of shrouded Low Pressure(LP) turbine.Compared with the No inter-Shroud gap's Leakage flow Model(NSLM) and With inter-Shroud gap's Leakage flow Model(WSLM),the aerodynamic characteristics and the heat transfer performance have been studied.Through the aerodynamic point of view,it is concluded that due to the pressure difference between the rotor's passage and the over-shroud cavity,in the stream-wise direction,flow structure has been modified,and the inter-shroud leakage flow may even cause flow separation in the vicinity of the blade passage's throat.In the circumferential direction,separation flows appear over the rotor's shroud surface(upper platform of the shroud).Meanwhile,from the point of view of heat transfer,further provision on contour maps of the non-dimensional Nusselt number reveals that the reattachment of leakage flow would enhance the heat transfer rates and endanger the rotor's labyrinth fins over the shroud.However,due to the limited amount of inter-shroud leakage flow(current computational model),temperature distribution variation along the blade surface(near the rotor's tip section) seems to have only minor insignificant differences.At the end of the paper,the author puts forward some recommendations for the purpose of future successful turbine design.