Measurements of the flow over a low-aspect-ratio cylinder mounted on a ground plane

The flow over a finite-height cylinder of aspect ratio 1, with one end mounted on a ground plane and the other end free, has been studied by means of surface flow visualisation, particle image velocimetry (PIV) and surface pressure measurements. The diameter-based Reynolds number was 200,000. The mean flow topology has been identified in three areas: the horseshoe vortex system, the separated flow over the free-end and the wake region. Evidence is shown for the existence of a three-horseshoe vortex system, while the mean flow over the free-end consists of an arch vortex with its bases on the forward half of the free-end. There are two tip vortices coming off the free-end. The wake region is found to be highly unsteady, with considerable variation from the mean flow.     

Experimental and numerical investigations of the deformation of soft materials under tangential loading

The surface ‘tensile test’, in which tangential loads are applied through surface mounted adhesive tapes, is a viable method for the assessment of mechanical properties of soft materials, particularly biological soft materials in vivo. In the present work the deformation pattern and force–displacement relationship in the surface tensile test were experimentally investigated using surface displacement analysis (SDA) and numerically simulated using finite element modelling. The experimental and FE results showed close agreement using silicone rubber as a model material. The force–displacement relationship was found to be dependent on the tape separations. SDA measurements and FE simulation showed that the displacement and strain fields were not uniform and the distribution pattern varies with tape separation. A combined experimental–numerical approach to inversely extract material properties using multiple tests with different length scales is proposed and assessed using a model material.     

A novel system for measuring liquid flow rates with nanoliter per minute resolution

An experimental system for liquid flow-rate measurements of pressure-driven flow through microchannels is described. The displacement of a meniscus is tracked in a precision borehole using a laser distance meter mounted on a feed-back controlled traversing stage. Successful measurements of flow rates as small as 30 pl/s are reported when using non-evaporative hexadecane, and evaporative fluids such as ethanol are measured at flow rates of 0.1 nl/s. The set-up can also be used for measurements in time-dependent flows. Finally, a discussion of the influence of dissolved nitrogen on the measured flow rates is given.     

Full-field strain measurements of the inside of an agricultural tyre using digital image correlation

This paper investigates strain measured on the inside of an agricultural tyre with large tread-blocks during a series of static tests using a novel measuring system. The full field strain measurements may be used in the development of a tyre which is capable of estimating tyre forces from strain measurements. The strain measurement system makes use of a calibrated stereo camera system on a mechanical stabilizing system that keeps the cameras pointed at the inside surface of the tyre in contact with the road while the wheel rotates. A static tyre test rig is used to displace the road surface relative to the tyre in the vertical and longitudinal direction. The large tread-blocks caused strain concentrations on the inner surface as the tyre deforms to comply with the road surface. Vertical and longitudinal tests each produce unique strain patterns in the contact patch region. Relationships between the applied forces and strain measurements were developed and showed that these relationships are near linear with R² values above 0.97. The strain measurements also show that the location where strain gauges, for single point strain measurements, are placed inside the tyre is very important on large lugged tyres.     

基于反向撞击法的JB-9014炸药Hugoniot关系测量

为了获得JB-9014未反应炸药的Hugoniot关系,在火炮加载平台上利用反向撞击技术对JB-9014炸药进行一维平面冲击实验。将JB-9014炸药样品作为飞片安装于弹托前表面,将镀膜氟化锂窗口作为装置靶。利用火炮加速弹托,使炸药样品以一定速度撞击镀膜氟化锂窗口,通过光子多普勒测速仪(photonic Doppler velocimetry,PDV)测量炸药样品击靶速度以及炸药/镀膜氟化锂窗口界面粒子速度。最终根据冲击波阵面守恒关系计算获得了JB-9014炸药冲击Hugoniot数据,采用正交回归直线拟合得到了炸药样品在3.1～8.2 GPa压力范围内的冲击Hugoniot关系:D_s=2.417+2.140u_s (D_s和u_s的单位均为km/s)。结果表明:该方法测试精度较高,响应时间快(小于5 ns),同时该方法可以对炸药的反应情况进行检测,便于判断实验是否测得真实的未反应炸药冲击Hugoniot数据。     

Introducing the theory of successful settling in order to evaluate and optimize the sedimentation tanks

A rectangular settling tank in full scale is investigated using the Fluent software to increase its efficiency. First, the pure water is simulated in the absence of particles. Then particles are injected into the flow field and tracked by means of the discrete phase model. Three methods are presented to optimize the settling tank: (1) adding a baffle which is mounted in the bottom and is extended up to the near of free surface, (2) adding a baffle which is mounted in the free surface and is extended up to the near of the tank bottom and (3) install a bi-directional baffle which is mounted in the free surface and is extended up to the near of the bottom. These three suggestions are checked using the short-circuiting phenomenon and the successful settling theory. The successful settling theory states that a particle can be accounted as a “trapped” particle if (1) settled particle stays static and stable in the tank bottom and (2) settled particle doesn’t return to purified sewage. Although the second method provided higher efficiency, the third method was selected as the most appropriate method in order to optimize the settling tank.     

Transition of boundary layer flows in the presence of Goertler vortices

Further experimental results on transition of boundary layer flows in the presence of streamwise counter-rotating Goertler vortices were obtained on concave test surface of 3.0 m radius of curvature. The test surface was mounted in a perspex (plexiglass) curved rectangular section duct connected to a low speed, blow down type, wind tunnel for a free-stream velocity range of 2.0 to 13.1 m/s. Velocity measurements were made using a single sensor hot-wire anemometer and boundary layer flow transitions were detected by a frequency spectrum method. The experimental results show a simple linear relationship between transition start position and free-stream velocity, and lie well between the limit lines of Goertler number transition criteria. It is found that the onset of transition at the flow upwash region occurs when the Goertler number based on the boundary layer momentum thickness reaches a value of about 7.5.     

Numerical study of heat transfer enhancement of finned flat tube bank fin with vortex generators mounted on both surfaces of the fin

Tube bank fin heat exchanger is one of the most compact heat exchangers, and it is widely used in industry equipments. The flat tube bank fin heat exchangers with vortex generators (VGs) have significant good heat transfer performance, and are used as radiators of locomotive. Here, we study heat transfer enhancement of a new fin where VGs are mounted on both surfaces of the fin. The heat transfer performance of this pattern is evaluated by a numerical method, and the results are compared with those obtained, under identical mass flow rate, when the VGs are mounted only on one surface of the fin. The results reveal that using this new pattern the height of VGs can be reduced and still obtain satisfactory heat transfer enhancement, while the pressure drop is reduced. The results also reveal that if VGs on one surface of the fin is determined, the locations where VGs are mounted on other surface of the same fin are very important, with configurations studied in this paper, depending on the value of Reynolds number, there exists an optimum location with which best heat transfer performance can be obtained.     

Evaluation of three techniques for wall-shear measurements in three-dimensional flows

Recent improvements in three techniques for measuring skin friction in two- and three-dimensional turbulent wall-bounded shear flows are presented. The techniques are: oil-film interferometry, hot wires mounted near the wall, and surface hot-film sensors based on MEMS technology. First, we demonstrate that the oil-film interferometry technique can be used to measure the skin-friction magnitude and its direction in two- and three-dimensional wall-bounded shear flows. Second, a simple method is outlined to measure the skin friction with a wall wire located outside of the viscous sublayer. Finally, a systematic study of the parameters influencing wall-friction measurements with MEMS sensors is presented. The results demonstrate that accurate measurements of the mean skin friction with MEMS sensors are possible in two- and three-dimensional wall flows. Measurements by the three techniques are compared to each other and to past measurements in the same facility.     

Residual Stress Determination Using Cross-Slitting and Dual-Axis ESPI

Hole-drilling and Electronic Speckle Pattern Interferometry (ESPI) are used to measure residual stresses in metal specimens. The slitting method is chosen as an alternative to the more commonly used hole-drilling method because it involves less material removal and leaves large areas of highly deformed material available to be measured. However the conventional single-slitting method is sensitive only to the stress component perpendicular to the slit direction, and thus has a strong directional bias. Conventional ESPI has a similar bias because it responds to surface displacements in a specific sensitivity direction. In this paper, a novel cross-slitting method with dual-axis ESPI measurements is proposed to address both directional biases. Cross-slitting is introduced as a means of releasing all in-plane stress components. The dual-axis ESPI system uses diagonal-mirror and shutter devices to provide surface displacement measurements in orthogonal in-plane directions. The combination of the cross-slit and dual-axis measurement gives isotropic sensitivity to the in-plane residual stress components. Experimental measurements are described that illustrate the capability and effectiveness of the cross-slitting/ESPI technique.     

Digital image correlation techniques for measuring tyre–road interface parameters: Part 2 – Longitudinal tyre slip ratio measurement

Measurement of tyre longitudinal slip-ratio is often estimated from three independent measurements devices namely wheel rotation speed, vehicle speed and tyre rolling radius. This produces an expensive measurement system to indirectly determine the slip-ratio. This paper presents a method by which the slip-ratio is determined from a video camera using digital image correlation techniques. The camera, mounted in such a way that the contact patch region is captured, enables the system to measure the tyre tread speed and ground speed at the contact patch. The slip-ratio is then determined from these two measurements.     

Investigation of the control of the flow around a wing using mini-flaps

The flow around an airfoil with a mini-flap mounted on the lower or upper wing surface is investigated. The results are obtained by measuring the pressure distribution over the airfoil surface and the forces acting on it for Mach and Reynolds numbers M = 0.1?0.8 and Re = (0.6?3.8) × 10⁶. It is shown that, as distinct from known devices such as Gurney flaps, blunt trailing edge, etc., for controlling the flow in the vicinity of the trailing edge of an airfoil, a mini-flap mounted on the undersurface produces gas flow from the upper to the lower surface around a sharp edge. In this case the flow pattern is considerably affected not only near the trailing edge but also over the entire airfoil. The pressure redistribution over the airfoil makes it possible to increase or decrease the wing lift. Thanks to the low hinge moment, the mini-flap can serve as an effective means of low-inertia control of the flow around a wing.     

An experimental investigation on the characteristics of fluid–structure interactions of a wind turbine model sited in microburst-like winds

An experimental investigation is performed to assess the characteristics of the fluid–structure interactions and microburst-induced wind loads acting on a wind turbine model sited in microburst-liked winds. The experiment study was conducted with a scaled wind turbine model placed in microburst-like winds generated by using an impinging-jet-typed microburst simulator. In addition to quantifying complex flow features of microburst-like winds, the resultant wind loads acting on the turbine model were measured by using a high-sensitive force–moment sensor as the turbine model was mounted at different radial locations and with different orientation angles with respect to the oncoming microburst-like winds. The measurement results reveal clearly that, the microburst-induced wind loads acting on the turbine model were distinctly different from those in a conventional atmospheric boundary layer (ABL) wind. With the scales of the wind turbine model and the microburst-like wind used in the present study, the dynamic wind loadings acting on the turbine model were found to be significantly higher (i.e., up to 4 times higher for the mean loads, and up to 10 times higher for the fluctuation amplitudes) than those with the same turbine model sited in ABL winds. Both the mean values and fluctuation amplitudes of the microburst-induced wind loads were found to vary significantly with the changes of the mounted site of the turbine model, the operating status (i.e., with the turbine blades stationary or freely rotating), and the orientation angle of the turbine model with respect to the oncoming microburst-like wind. The dynamic wind load measurements were correlated to the flow characteristics of the microburst-like winds to elucidate underlying physics. The findings of the present study are helpful to gain further insight into the potential damage caused by the violent microbursts to wind turbines to ensure safer and more efficient operation of the wind turbines in thunderstorm-prone areas.     

Non-Destructive Characterization of Subsurface Residual Stress Fields and Correlation with Microstructural Conditions in a Shot-Peened Inconel Component

Shot-peening is an important surface treatment used in a preventative way to guard against fatigue failures. The residual stress state imparted by shot-peening deters the formation and propagation of surface cracks. In this paper, we describe the measurement of residual stresses in an Inconel, IN100, sample using lattice strains measured using High Energy X-ray Diffraction (HEXD) and a Bi-Scale Optimization Method (BSOM). HEXD enabled rapid, non-destructive lattice strain measurements over a large region of the sample. Subsurface strains were obtained using a conical slit setup. The BSOM utilizes a macroscale representation of the sample and a spherical harmonic-based crystal scale representation of crystal orientation space at each experimental point (diffraction volume). A roughly biaxial stress state was predicted with a von Mises equivalent stress between 300 MPa and 400 MPa near the surface. The layer of material with high residual stress induced by shot-peening was found to be approximately 1 mm thick. Diffraction peak width, EBSD, and microhardness measurements were also made on the same sample, which rendered more qualitative measures of the plasticity-related effects of the shot-peening induced residual stress field. All of these measurements show a dimishing shot-peening plasticity with the increasing depth.     

Computerized instrumentation system for monitoring the tractor performance in the field

A high precision computerized instrumentation package was developed and mounted on a 50 kW tractor to monitor and measure various performance parameters of a tractor and implement system. The system was intended to be used for the compilation of a database of draft requirements of tillage implements. The system designed to measure: three-point linkage forces, ground speed, tillage depth, fuel consumption, forward speed, slip, engine speed, hydraulic pressure and fluid temperatures. The data acquisition unit was based on a high speed multi processors Campbell Scientific CR3000 data logger linked to a microcomputer using suitable transducer. The average calibration constants for the rear wheel speed, fuel consumption and three point linkage transducers were 0.0364 m/pulse, 0.000142857 l/pulse and 0.66 mV/kN respectively. The data acquisition system was capable of scanning rate up to 100 K sample/s. Data acquisition system was developed to measure draft of primary tillage implements in vertisol.     

Comparison of three residual-stress measurement methods on a mild steel bar

The objective of this investigation was to ascertain the surface residual-stress condition of a specially thermal-mechanically treated mild steel bar. Three methods of residual-stress measurement were used—two of them accurate, well-verified approaches and the third an experimental one. The first two were stress-relief blind-hole drilling (SRT) and X-ray diffraction (XRD), and the third was Barkhausen noise analysis (BNA). It is difficult to make direct comparisons between these methods since they each sample a different volume of material at different depths into the surface. However, the SRT data, when extrapolated to shallow depths sampled by the XRD, show excellent agreement with that nondestructive method. The BNA results show poor correlation with the XRD and SRT even with extrapolation to similar depths. The major reason for the poor BNA results seems to be its sensitivity to the microstructural conditions of the sample. All of the measurements, with the exception of one set of BNA measurements, indicate that tensile stresses existed in the surface of the specimen.     

高超音速湍流分离表面热流率的脉动特性

本文给出高超音速湍流分离不稳定特性的实验研究结果。试验条件是:自由流马赫数为 7.8,单位长度雷诺数为 3.5×10~7/米。分离流场由有限展长前向台阶产生,并用有高空间分辨率和快速响应的一列平齐安装的铂膜电阻温度计和多通道系统测量其表面热流率脉动。信号的条件采样分析结果表明:分离激波的根部由一束压缩波构成,流向展长约二分之一来流边界层厚度,在边界层外汇聚成单一主激波。这种激波结构极其不稳定,出现大尺度运动,流向运动的尺度约为分离激波上游影响区域长度的22％。激波振荡频率为一宽频带,主要集中在 1～3 千赫。在分离激波运动区域,热流脉动呈间歇性,在无扰动和激波扰动间跳跃。可以认为这种间歇性是分离激波系统大尺度振荡的结果。在激波运动区域的下游为分离区,流体继续压缩,热流脉动无间歇。     

A device to measure wheel slip to improve the fuel efficiency of off road vehicles

A hall sensor based simple technique was introduced to measure wheel slip and a microcontroller based embedded digital system was developed to display wheel slip data and warn the operator with audible and visible warnings if the optimum range is exceeds. Hall sensor slip measurement system was validated in controlled soil bin condition, tar macadam surface and actual field condition and compared with the commercial radar sensor. The developed system is simple in construction and can be mounted to any make and model of agricultural tractors by entering the appropriate rolling radius via the computer interface. Field trials were conducted to measure wheel slip and fuel consumption on farm use with and without activation of slip indicator; it was observed that, the amount of fuel saving during various agricultural operation was up 1.3 l/h.     

The effect of closed-loop feedback control on scalar mixing in a plane shear layer

The effect of feedback on mixing in a plane shear layer was studied using temperature as an analog to species concentration. Mixing was quantified using temperature measurements made by an array of cold-wire sensors. Upstream of the cold-wire sensors, a schlieren imager measured the cross-stream position of the temperature interface between the two streams before the primary vortical structures had formed. Surface heaters mounted on the flow partition were used as control actuators. Feeding the gained output from the interface position sensor back to the surface heaters closed the loop and created resonance and out-of-resonance conditions in the flow, both of which increased mixing. The feedback gains were adaptively modified in real time to maximize mixing at a given streamwise station. Finally, it was found that deliberately introducing streamwise vorticity, and then choosing feedback gains that strengthen these streamwise vortices, can greatly enhance mixing.     

纵向涡强化换热的实验研究

在流道内安装三角翼对涡发生器可以产生纵向涡旋,本文研究了Re＝800－8000范围内,以空气作为介质,涡发生器对加热片的强化换热效果,并通过红外热像仪测量加热片面的温度场,结果表明：与光滑加热片换热面比较,加装三角翼对涡发生器后,强化换热效果明显。本文条件下,在雷诺数为6000时,加装涡发生器整体强化换热效果达到50．8％。