Flow and deposition measurement of foam beads in a closed re-circulating wind tunnel for snowdrift modelling

A facility was created for flow and deposition measurement of foam beads (Expanded Polystyrene) in a closed re-circulating wind tunnel to model the snowdrift experimentally. The geometrical and flow similarities between the model (foam beads) and prototype (snow) particles were established for the wind tunnel experiments. The wind tunnel was instrumented with the electronic regulator, anemometer and newly developed flux measuring sensors along with a data logger to carry out the experiments for different simulated terrain conditions. An array of optical sensors for measurement of foam beads flux was calibrated with the known quantity of the material and used to find the flux variation with wind speed inside the tunnel. All three modes of drifting transportation namely creeping, saltation and suspension could be observed through the transparent acrylic wall for data collection. The threshold velocity of foam bead movement was 4.05 m/s in the horizontal section and same was 2.7 m/s in the inclined section at an angle of 30° downward (a critical angle of avalanche starting zone). The process of snow deposition by the snow fence was simulated with the foam beads deposition around the scaled model (1:50) of a snow fence in the wind tunnel. The experiments helped to find a flow measuring technique for light drifting material like foam beads and the modelling of drifting snow.     

An experimental analysis of the effect of wind load on the stability of a container crane

This study was conducted to analyze the effects of wind loads on the stability of a 50-ton container crane using wind tunnel testing. The experiments were performed in order to furnish designers with data that can be used in the design of a container crane that is wind resistant, assuming an applied wind load of 75 m/s velocity. Data acquisition conditions for this experiment were established in accordance with similarity to a reduced-scale model. The scale of the container crane model, wind speed and time were selected as 1/200, 1/13.3, and 1/15, respectively, and the experiment was conducted using an Eiffel type atmospheric boundary-layer wind tunnel having a 11.52 m² cross-sectional area. All directional drag and overturning moment coefficients were investigated and uplift forces due to wind load at each supporting point were analyzed.     

Improvement of the five-hole probe calibration using artificial neural networks

In the present study, the artificial neural networks (ANNs) technique was implemented to link non-dimensional pressure coefficients and flow characteristics to calibrate a five-hole probe. The experimental data of this work were obtained from a subsonic open-circuit wind tunnel at the velocity of 10 m/s. Here, the efficiency of ANNs was compared with two conventional data reduction methods, including linear interpolation technique and 5^th-order polynomial surface fit algorithm. Based on the statistical parameters of calibration data, it was concluded that the radial basis function (RBF) algorithm was more accurate and had more flexibility compared to the multi-layer perceptron (MLP) regression algorithm, the linear interpolation and 5^th-order polynomial methods. In the RBF method, the mean absolute errors of 0.11, 0.64, 0.02 and 0.03 were achieved for α, β, Cp_t and Cp_s , respectively. Furthermore, the effects of training data reduction and data selection on the performance of RBF were studied. The accuracy of the proposed RBF method was analyzed at different α angles and for random test data. Finally, the influence of increasing number of test data on the efficiency of calculated RBF method was evaluated.     

Direct measurement of skin-friction in shock/boundary-layer interaction flows

The direct measurement of skin friction at high speed is extraordinarily complicated due to the interference from various extraneous forces and the short test-time of high-speed facilities. The present study deals with the design and performance assessment of a skin friction sensor in a hypersonic flowfield with shock-boundary layer interaction, which is a predominant high-speed flow phenomenon. The experiment was conducted in the IIT Bombay Shock Tunnel (IITB-ST); the sensor was exposed to a flow with freestream Mach number, total enthalpy, and Reynolds number of 8.4, 0.69 MJ/kg, and 2.60 × 10⁶ m⁻¹, respectively. The shock-boundary layer interaction was induced by an oblique shock impinged on a flat plate, with a flow turn angle of 15°. The low magnitude average skin friction could be measured with an uncertainty of ±21%. The comprehensive study conducted confirmed the suitability of the skin friction sensor for high-speed applications in impulse facilities.     

Torque loss of type C40 FZG gears lubricated with wind turbine gear oils

Five fully formulated wind turbine gear oils were characterised. The gear oils have 320 ISO VG grade and different formulations: ester, mineral, PAO, PAG and mineral+PAMA.A back-to-back FZG test machine, with re-circulating power, was used and a torque-cell was included on the test rig in order to measure the torque loss. Eight thermocouples were included to monitor the temperatures in different locations of the test rig.Tests at 1.13, 2.26 and 6.79 m/s were performed for different FZG load stages: K1, K5, K7 and K9. Both gearboxes were jet-lubricated with an oil flow of 3 l/min. The input flow temperature was kept almost constant (80 ±1 °C).Friction generated between the meshing teeth, shaft seals and rolling bearing losses was predicted.     

Management of the wind speed data using adaptive neuro-fuzzy methodology

In this paper, the accuracy of the Weibull model of wind speed is evaluated using an adaptive neuro-fuzzy inference system (ANFIS) based on wind data. The wind data comprises of wind speed measurements in the city of Nis in Serbia at different heights of 10 m, 30 m and 40 m for duration of one year. The ANFIS results are compared with the experimental results and Weibull model using root-mean-square error (RMSE), coefficient of determination, and Pearson coefficient. The effectiveness of the proposed unified strategy is verified based on the simulation results.     

A wind tunnel for anemometer calibration in the range of 0.2-1.25 m/s

In order to calibrate different types of anemometers in a low-speed range (0.2-1.25 m/s) using pressure measurements, a wind tunnel has been built and characterized. The wind tunnel has a low-speed section and a high-speed section. The wind tunnel calibration has been performed by means of comparison of airspeed at the test cross section (low-speed) and at the reference cross section (high-speed). Measurements have been taken with a calibrated hot-wire anemometer and static and total probes respectively. A linear fitting is used to relate reference and test airspeed. A model based on mass conservation law has been developed. Calculations have been made with and without introducing the effect of the speed profile. Uncertainties of the experimental calibration are presented.     

Wind speed and direction measurement based on arc ultrasonic sensor array signal processing algorithm

This article investigates a kind of method to measure the wind speed and the wind direction, which is based on arc ultrasonic sensor array and combined with array signal processing algorithm. In the proposed method, a new arc ultrasonic array structure is introduced and the array manifold is derived firstly. On this basis, the measurement of the wind speed and the wind direction is analyzed and discussed by means of the basic idea of the classic MUSIC (Multiple Signal Classification) algorithm, which achieves the measurements of the 360° wind direction with resolution of 1° and 0–60 m/s wind speed with resolution of 0.1 m/s. The implementation of the proposed method is elaborated through the theoretical derivation and corresponding discussion. Besides, the simulation experiments are presented to show the feasibility of the proposed method. The theoretical analysis and simulation results indicate that the proposed method has superiority on anti-noise performance and improves the wind measurement accuracy.     

Development of an air velocity and flow measurement system by using a novel circular disc

In this paper, development of a sensor using a circular disc for air velocity measurement based on the drag force equation is proposed. The air velocity measurement sensor is basically designed with a load cell in order to determine the drag force. The circular disc is used for creating a drag force, and by using load cell, the drag force that acts on the circular disc is measured. As the circular disc's drag coefficient can be considered constant at Reynolds numbers between 10³ and 10⁶, it can be possible to obtain the explicit equation of drag force. The remaining components of drag force equation are obtained by measurement. The proposed air velocity measurement sensor is characterized by wind tunnel measurements. All measurements were performed in an ISO/IEC 17025 accredited calibration laboratory – the Wind Tunnel of Turkish State Meteorological Service. The characterization measurements were performed at air velocities between 1 m/s and 20 m/s. The correction factors were calculated and a calibration curve for the proposed air velocity measurement sensor was obtained. The calibration curve's linearity was higher than 0.99 and a comparison the results from a Micromanometer with Pitot-Tube shows that for the designed working range, the sensor has an acceptable performance for time-averaged air velocity measurements according to the requirements of the World Meteorological Organization.     

Investigation of high-pressure micro jet technology as an alternative to diamond disc conditioning in ILD CMP

The efficacy of an alternative to conventional diamond conditioning in chemical mechanical planarization (CMP) was evaluated in this study. The high pressure micro jet (HPMJ) system sprays ultra-pure water (UPW) at pressures ranging from 10 to 20 MPa onto a CMP pad to clean the pad of slurry residue, remove embedded slurry particles, and re-establish pad asperities. The system is employed in an ex situ fashion and is compared to in situ and ex situ diamond conditioning as well as using no conditioning. Real-time frictional force acquisition allows for coefficient of friction (COF) analysis, which indicates the extent of pad wear. Removal rate analysis, SEM imagery, and pad surface profilometry are also used to evaluate HPMJ as an alternative conditioning technology. Removal rates significantly lower than those associated with diamond conditioning are obtained for the HPMJ system when UPW conditioning is directly followed by polishing. SEM imagery and pad profilimetry indicate these low HPMJ removal rates are due to differences in pad surface chemistry, not pad surface topography. Experiments including a 30 s silicon wafer polish with slurry following HPMJ conditioning to re-establish pad surface chemistry were performed and result in removal rates that are comparable to those obtained using ex situ conditioning. The removal rates obtained using HPMJ conditioning for relative wafer-platen velocities of 0.31 and 0.62 m/s are 8 and 1% higher than those obtained using ex situ diamond conditioning and 18% lower than those obtained using ex situ diamond conditioning for 0.93 m/s. The average COF values for HPMJ conditioning using the intermediate silicon wafer polishes are 15% lower than average COF values associated with ex situ diamond conditioning, suggesting a possible increase in pad life for the HPMJ system.     

Blow-down calibration of a large ultrasonic flow meter

Oil and gas production industries use large (diameter > 0.8 m) ultrasonic flow meters (USMs) to measure exhaust gas from flare stacks, emissions from smokestacks, flow of natural gas, etc. Since most flow laboratories do not have compressors with sufficient flow capacity (>10 kg/s) to calibrate large flow meters, calibrations are performed using the blow-down method where flow is generated by discharging high pressure tanks, leading to significant flow transients. We used an array of critical flow venturis (CFVs) in a blow-down facility to calibrate a large (D = 89.5 cm) 8-path ultrasonic flow meter. The flow transients associated with the blow-down process caused large spatial and temporal variations in temperature that dominated (40%–67%) the uncertainty budget. Our uncertainty analysis accounts for transient-generated uncertainties and provides guidelines for improving blow-down calibrations of large flow meters.     

Nanosys-1000机床静压止推轴承流场分布规律及承载特性

为了提高Nanosys-1000非球面曲面光学零件超精密加工机床加工精度,研究了机床核心部件静压止推轴承内流场分布规律,进而揭示其承载特性。利用ANSYS/Fluent软件建立对称结构静压止推轴承扇形油垫的仿真模型,采用层流模式对进油压力为1.3~1.9 MPa、油膜厚度为20~36 μm的油垫流场分布规律与承载特性进行分析。研究结果表明：油垫内压力在油腔区域比较均匀,沿封油边呈线性下降;油膜承载力随油腔压力线性增长,且在同一进油压力下,油膜厚度越小,油膜承载力越大,进油压力为1.5 MPa时,油膜厚度从36 μm减小到20 μm,油腔压力从3.05×10⁵ Pa增加到8.02×10⁵ Pa,油膜承载力相应地从880 N增加到2 109 N;同一负载即油膜承载力下,进油压力越高,油膜厚度越大,油膜承载力为1 320 N时,进油压力从1.3 MPa增加到1.9 MPa,油膜厚度从26 μm增加到30 μm;同一油膜厚度下,进油压力越高,润滑油流量越大,油膜厚度为28 μm时,进油压力从1.3 MPa增加到1.9 MPa,润滑油流量从0.179 L/min增加到0.231 L/min。相关研究结果在研制的Nanosys-1000非球面曲面超精密加工机床静压止推轴承上得到了验证。     

In Situ Growth of Graphene on Carbon Fabrics with Enhanced Mechanical and Thermal Properties for Tribological Applications of Carbon Fabric–Phenolic Composites

ABSTRACT

Though the premature failures of wind turbine gearboxes are often attributed to bearing fatigue from overloading, there is compelling evidence that wear from underloading is a significant contributor. Here we attempt to gain insight into the relative contributions of over- and underloading by assessing planet bearing reaction forces from the Gearbox Reliability Collaborative (GRC) standard gearbox within a typical utility-scale wind turbine under realistic conditions. The results demonstrate that non-torque load sharing by the planetary stage increases and decreases planet bearing reaction forces at different locations within each rotor cycle regardless of wind speed. Planet bearing reaction forces exceeded the fatigue limit at wind speeds above 12 m/s and fell below the minimum load rating at wind speeds below 7 m/s. Based on analyses of published wind spectra from 10 U.S. sites, the expected fatigue life of the planet bearings ranged from 42 to 529 years even after accounting for non-torque load sharing. At the same 10 sites, planet bearings were underloaded (below 2% of the dynamic load rating) once per rotor cycle 40–70% of the time. Underloaded bearings are susceptible to surface damage when suddenly exposed to common transient events, such as yaw, wind gusts, braking, and grid faults. The resulting surface damage can initiate premature failure via wear (e.g., micropitting) or by reducing bearing fatigue life. The results suggest that carrier bearing clearance, non-torque load sharing, and planet bearing underloading are significant contributors to the premature failures of wind turbine planet bearings.     

Reproduction of air velocity in the entrance region of the test pipe in a wind tunnel

The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.     

Robust model of a transient wind tunnel for off-design aerothermal testing of turbomachinery

Short duration wind tunnels offer an economical approach to study the aero-thermal operation of propulsion components, while reproducing temperature ratios, Reynolds and Mach numbers of the actual engine conditions. The present paper aims at modeling with high fidelity the von Karman Institute compression tube facility. This wind tunnel was simulated using the EcosimPro suite to characterize the behavior of each subcomponent during the whole test envelope, including the turbine map at off-design. The numerical predictions were then assessed through the comparison with experimental data. The model was proven to be an effective tool to accurately evaluate all the operating regimes that a research turbine experienced during the experimental sequence. Consequently, the present model allows exploiting the complete test run duration to obtain unique experimental data from the turbomachinery operating at far off-design conditions. The capability to experimentally test components at off-design is fundamental to understand the flow physics of any gas turbine engine operating at extreme conditions and to characterize the transient performances of fluid-machinery in high-speed propulsion concepts. However, technical dissemination on these aspects is scarce.     

PSV and marker detection techniques for investigating the wake of an oscillating cylinder in a large wind tunnel

Although Particle Image Velocimetry techniques are widely used in the experimental investigation of the flow structure around obstacles, the application of these techniques in wind tunnels is frequently limited by the dimension of the areas involved, which make the image acquisition set-up expensive.This paper examines the use of Particle Streak Velocimetry (PSV) and marker detection techniques to measure the flow field around bodies with relatively large dimensions. In spite of its minimal requirements in terms of acquisition set-up, the method permits the investigation of complex phenomena.The tests described in the paper were carried out in air using a rigid cylinder, free to oscillate in a wind tunnel. Coupling PSV and marker detection techniques with the phase average of the measured velocity fields, the evolution of vortex shedding behind a cylinder with a diameter of 200 mm was measured with an acquisition area of about 1000×1200 mm.     

Refined reconstruction of liquid–gas interface structures for stratified two-phase flow using wire-mesh sensor

Wire-mesh sensors (WMS), developed at HZDR [4], [13], are widely used to visualize two-phase flows and measure flow parameters, such as phase fraction distributions or gas phase velocities quantitatively and with a very high temporal resolution. They have been extensively applied to a wide range of two-phase gas–liquid flow problems with conducting and non-conducting liquids. However, for very low liquid loadings, the state of the art data analysis algorithms for WMS data suffer from the comparably low spatial resolution of measurements and from boundary effects, caused by e.g. flange rings – especially in the case of capacitance type WMS. In the recent past, diverse studies have been performed on two-phase liquid–gas stratified flow with low liquid loading conditions in horizontal pipes at the University of Tulsa. These tests cover oil–air flow in a 6-inch ID pipe and water–air flow in a 3-inch ID pipe employing dual WMS with 32×32 and 16×16 wires, respectively. For oil–air flow experiments, the superficial liquid and gas velocities vary between 9.2 m/s≤ν_SG≤15 m/s and 0.01 m/s≤ν_SL≤0.02 m/s, respectively [2]. In water–air experiments, the superficial liquid and gas velocities vary between 9.1 m/s≤ν_SG≤33.5 m/s and 0.03 m/s≤ν_SL≤0.2 m/s, respectively [17], [18]. In order to understand the stratified wavy structure of the flow, the reconstruction of the liquid–gas interface is essential. Due to the relatively low spatial resolution in the WMS measurements of approximately 5 mm, the liquid–gas interface recognition has always an unknown uncertainty level. In this work, a novel algorithm for refined liquid–gas interface reconstruction is introduced for flow conditions where entrainment is negligible.     

New air speed calibration system at NMIJ for air speeds up to 90 m/s

National Metrology Institute of Japan (NMIJ) has established a high air speed standard facility and has been providing a calibration service since 2015. The facility has an air speed range of 40 m/s to 90 m/s with a relative expanded uncertainty (k = 2) of 0.63%. The purpose of this primary standard is mainly to contribute to the improvement of meteorological observation research and to the evaluation of flow field inside a turbo machine and around a high speed vehicle. The reference air speed is derived from the national primary gas flowrate standard of Japan. A conversion device from flowrate to air speed is installed in the test line of the closed-loop calibration facility. The reference air speed at the nozzle exit of the conversion device is obtained by comparing the integral of the air speed profiles and the reference volume flowrate. The total pressure tube used as a transfer standard is then calibrated against the reference air speed at the center of the nozzle exit. The Eiffel-type wind tunnel, which is a working standard for the daily calibration service, is calibrated using this total pressure tube. The present paper describes the calibration system, the traceability chain, and an uncertainty analysis using a validation method.     

The Tribological Behaviour of Fe–28Al–5Cr/TiC Under Liquid Paraffine Lubrication

The tribological behaviour of Fe–28Al–5Cr and its composites containing 15, 25 and 50 wt% TiC (corresponding to 19.3, 31.2 and 57.6 vol%), produced by hot-pressing process, was investigated under liquid paraffine lubrication against an AISI 52100 steel ball in ambient environment at varied applied loads and sliding speeds. It was found that the wear resistance increased and friction coefficient decreased with increasing of TiC content. The coefficients of friction are in the range of 0.09–0.14 at the given testing conditions. The wear rates of all the materials except the 50% composite are on the order of 10⁻⁶–10⁻⁵ mm³ m⁻¹, the wear rate for the 50% composite is too low to quantify under the two sliding conditions, (50 N, 0.04 m/s) and (100 N, 0.02 m/s). The wear rates of all the materials increase as applied load increases and the increasing extent diminishes with the increase of TiC content, but first increase slightly and then nearly remains steadiness with increasing sliding speed. The 50 wt% composite has wear resistance about 7–20 times better than pure Fe–28Al–5Cr at different sliding parameters. The enhanced wear resistance by TiC addition is attributed to the high hardness of the composites, as well as support of the oil lubrication film/layer by the hard TiC phase. The worn surfaces of all the materials are analyzed by a scanning electron microscope. The dominant wear mechanism of the Fe–28Al–5Cr and 15% composite is grooving and flaking-off, but those of the 25 and 50% composites are mainly shallow grooving.