Hot-wire System Research Articles

Gun식 가스버너의 난류유동장 발달에 미치는 슬릿과 스월베인의 영향

This paper is studied to investigate the effect of slits and swirl vanes on the development of turbulent flow fields in gun-type gas burner with a cone type baffle plate because this gas burner is generally composed of eight slits and swirl vanes. All of turbulent characteristics including mean velocities were measured in the horizontal plane and cross section by using X-type hot-wire probe from hot-wire anemometer system. This experiment is carried out at flow rate 450/min in the test section of subsonic wind tunnel. Slits cause the fast jets, and then they have the characteristic that the flow is not adequately spread to radial direction and has long flow length and very small flow velocity distribution in the central part. On the contrary, swirl vanes does not have long enough for adequate flow length to downstream because the rotational flow diffuses remarkably to radial direction. However, the suitable arrangement between slits and swirl vanes causes effective flow width and flow length, and then it promotes fast flow mixing over the entire region including central part to increase turbulence more largely and effectively. Therefore, it is thought as a very desirable design method in gun-type gas burner to locate slits on the outside of swirl vanes.

Modeling and measurement of film deposition in a one-dimensional hot-wire CVD system

A novel hot-wire chemical vapor deposition (HW-CVD) geometry was employed to study the deposition of Teflon-like films from hexafluoropropylene oxide (HFPO). In this configuration hot wires were replaced by thin ribbons, and under proper operating conditions the complex HW-CVD geometry is simplified to a one-dimensional system. The kinetics of both HFPO decomposition and Teflon deposition were measured as a function of operating conditions. A hybrid 2-D CFD/1-D stagnation flow model was used to interpret the results. At relatively low ribbon temperatures good agreement between model and experiment was observed. Deviations observed at higher ribbon temperatures were attributed to gas-phase polymerization of CF 2 moieties, and participation of these oligomers in the deposition process.

콘형 배플판을 갖는 Gun식 가스버너의 난류유동장에 대한 슬릿과 스월베인의 역할

The gun-type gas burner adopted in this study is generally composed of eight slits and swirl vanes. Thus, this paper is studied to investigate the effect of slits and swirl vanes on the turbulent flow fields in the horizontal plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rate 450 /min in the test section of subsonic wind tunnel. The axial mean velocity component in the case of burner model with only swirl vanes shows the characteristic that spreads more remarkably toward the radial direction than axial one, it does, however, directly opposite tendency in the case of burner model with only slits. Consequently. both slits and swirl vanes composing of gun-type gas burner play an important role in decrease of the speed near slits and increase of the flow speed in the central part of a burner because the biggest speed spurted from slits encircles rotational flow by swirl vanes and it drives main flow toward the axial direction. Moreover, the turbulent intensities and turbulent kinetic energy of gun-type gas burner are distributed with a fairly bigger size within X/R

A multi-sensor hot-wire anemometer system for investigation of wall-bounded flow structures

This work describes a hot-wire anemometer system and an experimental procedure designed for mapping of the flow structure in disturbed boundary layers. It also briefly presents results from periodically disturbed wing boundary layers. The hot-wire system consists of a number of individual anemometer units, which can be combined to operate multi-sensor probes for simultaneous measurement of velocities in many points. In the present paper, however, only a single probe was used mounted in a dedicated traverse system in order to demonstrate how ensemble averaging can provide knowledge about the growth and decay of organised flow structures, as long as they are periodic in both time and space. The information from this flow structure can then be used in the design of multi-array hot-wire probes for further studies of the non-deterministic stages of the boundary layer transition.

Aerodynamic Design and Experimental Investigation of the Sailplane Wing Tip Devices

This paper describes an experimental set-up for the investigation of wing tip devices developed as part of a study into the velocity and vorticity distributions in the flow field behind winglets, using hot-wire anemometry. In this study, effort was focused on gaining a greater understanding of what happens in the region where the winglet joins the wing. The measurements were performed in the Handley-Page wind tunnel of the Department of Aerospace Engineering at the University of Glasgow. In order to carry out measurements with the hot-wire anemometry system, a new traverse mechanism was designed and manufactured. This traverse mechanism was integrated with the other test instrumentation to create a complete measurement chain. The complete system allows fully automated hot wire measurements to be made over a defined area using programmable test parameters.

Reliable tidal volume estimates at the airway opening with an infant monitor during high-frequency oscillatory ventilation

To assess the suitability of a hot-wire anemometer infant monitoring system (Florian, Acutronic Medical Systems AG, Hirzel, Switzerland) for measuring flow and tidal volume (Vt) proximal to the endotracheal tube during high-frequency oscillatory ventilation. In vitro model study. Respiratory research laboratory. In vitro lung model simulating moderate to severe respiratory distress. The lung model was ventilated with a SensorMedics 3100A ventilator. Vt was recorded from the monitor display (Vt-disp) and compared with the gold standard (Vt-adiab), which was calculated using the adiabatic gas equation from pressure changes inside the model. A range of Vt (1-10 mL), frequencies (5-15 Hz), pressure amplitudes (10-90 cm H2O), inspiratory times (30% to 50%), and Fio2 (0.21-1.0) was used. Accuracy was determined by using modified Bland-Altman plots (95% limits of agreement). An exponential decrease in Vt was observed with increasing oscillatory frequency. Mean DeltaVt-disp was 0.6 mL (limits of agreement, -1.0 to 2.1) with a linear frequency dependence. Mean DeltaVt-disp was -0.2 mL (limits of agreement, -0.5 to 0.1) with increasing pressure amplitude and -0.2 mL (limits of agreement, -0.3 to -0.1) with increasing inspiratory time. Humidity and heating did not affect error, whereas increasing Fio2 from 0.21 to 1.0 increased mean error by 6.3% (+/-2.5%). The Florian infant hot-wire flowmeter and monitoring system provides reliable measurements of Vt at the airway opening during high-frequency oscillatory ventilation when employed at frequencies of 8-13 Hz. The bedside application could improve monitoring of patients receiving high-frequency oscillatory ventilation, favor a better understanding of the physiologic consequences of different high-frequency oscillatory ventilation strategies, and therefore optimize treatment.

円筒壁面上を軸方向に流出する円形噴流

This paper is concerned with the water circular jet flow issuing along the circular cylinder wall. Especially, attention is focused on the flow aspect in the cross section normal to the jet flow. This flow aspect at several down-stream locations has been visualized by the system composed of the dual-pulse YAG-laser, the CCD-camera, the CRV and the PIV. The visualized image information has been compared with the experimental results obtained by the hot-wire anemometer system, which have been already presented in the previous paper. As a result, the interesting flow aspect obtained from the velocity contour maps in the previous experiment has been explained by using this image processing results.

Influence of the Unsteady Wake on the Flow and Heat Transfer in a Linear Turbine Cascade

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

An Experimental Study on the Three Dimensional Turbulent Flow Characteristics of Swirl Burner for Gas Furnace

This paper represents the vector fields, three dimensional mean velocities, the turbulent intensities, the turbulent kinetic energy, and the Reynolds shear stresses in the X-Y plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rates 350 and 450l/min respectively, which are equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of subsonic wind tunnel. The vector plot shows that the maximum axial mean velocity component exists in the narrow slits situated radially on the edge of gas swirl burner, for that reason, there is some entrainment phenomena of ambient air in the outer region of burner. Moreover, mean velocities in the initial region are largely distributed near the outer region of burner at Y/R≒0.97, but they diffuse and develop into the center flow region of burner according to the increase of axial distance. The turbulent intensities and the turbulent kinetic energy due to large inclination of mean velocity and swirl effect show that the maximum value in the initial region of burner is formed in the narrow slits situated radially on the edge of gas swirl burner and large values are mainly formed in the entire region of burner after X/R=2.4358, hence, the combustion reaction is anticipated to occur actively near this region. And the Reynolds shear stresses are also largely distributed from slite to vanes of gas swirl burner in the intial region, but their values largely disappear after X/R=3.2052.

Turbulent flow field structure of initially asymmetric jets

The near field structure of round turbulent jets with initially asymmetric velocity distributions is investigated experimentally. Experiments are carried out using a constant temperature hot-wire anemometry system to measure streamwise velocity in the jets. The measurements are undertaken across the jet at various streamwise stations in a range starting from the jet exit plane and up to a downstream location of twelve diameters. The experimental results include the distributions of mean and instantaneous velocities, vorticity field, turbulence intensity, and the Reynolds shear stresses. The asymmetry of the jet exit plane was obtained by using circular cross-section pipes with a bend upstream of the exit. Three pipes used here include a straight pipe, and 90 and 160 degree-bend pipes. Therefore, at the upstream of the pipe exit, secondary flow through the bend and mean streamwise velocity distribution could be controlled by changing the curvature of pipes. The jets into the atmosphere have two levels of initial velocity skewness in addition to an axisymmetric jet from a straight pipe. In case of the curved pipe, a six diameter-long straight pipe section follows the bend upstream of the exit. The Reynolds number based on the exit bulk velocity is 13,400. The results indicate that the near field structure is considerably modified by the skewness of an initial mean velocity distribution. As the skewness increases, the decay rate of mean velocity at the centerline also increases.

Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.

A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.

The Use of Hot-Wire Anemometry to Investigate Unsteady Wake-Induced Boundary-Layer Development on a High-Lift LP Turbine Cascade

Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds numbers. Compared to steady flow, a reduction of total pressure loss coefficient over a broad range of Reynolds numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading. Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane. Unsteady flow causes the transition on the surface of the suction side of a low-pressure turbine blade to move upstream whenever an incoming wake is present on the surface; moreover, a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot wire data acquisition system is required. Due to the fact that hot wires give a good insight into boundary layer development, a new hot-wire data acquisition system has been set up. The anemometry system can acquire four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilized for a once-per-revolution trigger. The once-per-revolution trigger is used to start the measurement of one data block. Using the well-established ensemble-averaging technique, 300 ensembles each consisting of five wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction. The adaptation of this new hot-wire anemometry data acquisition system to the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen is pointed out. First, results on unsteady periodic boundary layer development of a highly loaded low-pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from x/lax=0.82 to x/lax=0.99 (suction side), at steady and unsteady inlet flow conditions Ubar=10 m/s at an outlet Reynolds number of Re2th=100,000 have been conducted. [S0889-504X(00)00204-X]

Flying hot-wire measurements in an axisymmetric sudden expansion

An apparatus was designed and fabricated so that hot-wires could be used to obtain velocity measurements in an axisymmetric sudden expansion. The recirculating flow that exists in a sudden expansion and the directional insensitivity of hot-wires, required a device that would propel the hot-wires through the flow field faster than the flow was recirculating. Such a device, termed a “flying” hot-wire system, literally collected data “on the fly”. The sudden expansion facility has an expansion ratio of 3:1; and all of the measurements were at a Reynolds number of 41,000 based on bulk velocity and inlet pipe diameter. Significant simultaneous multi-point cross-wire measurements were obtained using this system. From these measurements, the mean velocities and normal stresses in all three directions as well as the dominant shear stress could be calculated as a function of streamwise distance. These quantities were used to perform a kinetic energy balance between the mean convection, production, turbulent diffusion and dissipation. From this energy balance, knowledge of the spatial variation of the isotropic dissipation was obtained. From these measurements, the velocity two-point correlation tensor, a quantity difficult to obtain in a separated flow, was calculated. In this paper, the two-point correlation tensor is utilized to calculate the integrated length scales in this flow geometry at several downstream locations.

A four-sensor hot-wire probe system for three-component velocity measurement

A velocity measurement system based on a miniature four-sensor hot-wire probe capable of simultaneous three-component measurements throughout a wide range of flow angles has been developed. The calibration technique allows measurements to be made throughout the acceptance cone of the probe without being restricted by the errors associated with analytic angle response equations. This technique is based upon look-up tables with values which tend to vary slowly, allowing a simple interpolation scheme to be used. Measurements made in a turbulent pipe flow verify the accuracy of the technique.

A Triple Hot-Wire System for Indoor Air Flow Measurements

The application of a home made, triple hot-wire system in indoor air flow measurements is presented. Both the anemometer and sensor have been developed at Athens University with the aim to provide a reliable, research tool of reasonable cost, simple construction, and satisfactory performance. All three velocity components above a threshold of 10 cm s−1 can be measured. The system is also equipped with two thermometers for measuring the mean and fluctuating air temperature and for providing a means of temperature compensation of the hot wires’ signal. After evaluation of the system in the laboratory, it was used in the measurement of the velocity profile of flows driven by the temperature difference between two internal zones. The implied accuracy of the method allows for its integration with measurements of air volume exchange rates between internal zones, as estimated by tracer gas techniques.

A study of the three-dimensional interaction of wakes and boundary layers

SummaryThis paper concerns the study of the three-dimensional interaction of a slat wake and a wing boundary layer, as commonly occurs on the suction surface of a high-lift rnulti-element aerofoil. The experimental test case has a realistic slat-wing flow configuration under infinite swept wing conditions. This enables the effect of the cross flow induced by the wing sweep on the slat wake and the wing boundary layer interaction process to be investigated. A triple hot-wire system has been used to measure the mean velocity and Reynolds stress components in the flow field. The measurements are used to validate a three-dimensional boundary layer code, which has been modified to calculate this three-dimensional wake-boundary layer mixing flow.

Improvements in the Production System for Green Lacewings: An Adult Feeding and Oviposition Unit and Hot Wire Egg Harvesting System

Abstract Green lacewings ( Chrysoperla spp.) are used in augmentative release programs against a variety of arthropod pests. As part of an ongoing research program to improve the mass production technology for green lacewings, an Adult Feeding and Oviposition Unit (AFOU) and a hot wire egg harvesting system were developed. The AFOU is a cylindrical unit, which can be unrolled to facilitate egg harvest with a hot wire system. The hot wire egg harvesting system consists of two devices, one of which uses a pneumatic cylinder to pull the cylinder portion of the AFOU past the hot wire and the other which is used to harvest eggs from the top of the AFOU. These improvements make adult handling and egg harvesting easier. The improved system requires less manual labor than the conventional paper cartons and manual egg harvesting system commonly used in the United States. Egg recovery was higher when a hot wire egg harvesting system was used than when the traditional loose ball of nylon netting was used. There was no difference in the percentage hatch of eggs recovered with either of these systems or with a sodium hypochlorite based egg harvesting system. This equipment may provide the basis for an automated adult handling and egg harvesting system for the mass production of green lacewings.

Velocity and Turbulence Intensity Distributions of Developing Turbulent Pulsating Flows in Square Duct.

Turbulent pulsating air flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms, the mean and turbulence components of the axial velocity, and the entrance length are obtained as major characteristics of the developing turbulent pulsating flows. An inviscid flow theory coupled with the quasi-steady wall shear stress assumption is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed previously. The local turbulence intensity is found to be slightly weaker in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large as the hydraulic diameter.

Simultaneous Measurements of Three Velocity Components by a Flying Hot-Wire Method Using an X-Array Hot-Wire Probe. 2nd Report. Calibration Technique and Its Application to a Flow Field Downstream of a Vortex Generator.

This paper proposes a calibration technique for a flying hot-wire method that uses with an X-array hot-wire probe. The flying hot-wire system moves the hot-wire probe in the spanwise Z-direction of the flow field. The calibration of yaw and pitch angle sensitivities of the probe is of utmost importance to this system. After careful calibration, the system is applied to a three-dimensional flow to obtain three components of the mean velocity and six components of the Reynolds stress. The mean velocities and the Reynolds shear stresses downstream of a pair of vortex generators embedded in a two-dimensional boundary layer show the same profiles as those obtained with an ordinary X-array hot-wire probe. In one traverse, the flying hot-wire system can measure 60 points of six components of the Reynolds stress with good accuracy.

Influence of Mainstream Turbulence on Heat Transfer Coefficients From a Gas Turbine Blade

The influence of mainstream turbulence on surface heat transfer coefficients of a gas turbine blade was studied. A five-blade linear cascade in a low-speed wind tunnel facility was used in the experiments. The mainstream Reynolds numbers were 100,000, 200,000, and 300,000 based on the cascade inlet velocity and blade chord length. The grid-generated turbulence intensities at the cascade inlet were varied between 2.8 and 17 percent. A hot-wire anemometer system measured turbulence intensities, mean and time-dependent velocities at the cascade inlet, outlet, and several locations in the middle of the flow passage. A thin-foil thermocouple instrumented blade determined the surface heat transfer coefficients. The results show that the mainstream turbulence promotes earlier and broader boundary layer transition, causes higher heat transfer coefficients on the suction surface, and significantly enhances the heat transfer coefficient on the pressure surface. The onset of transition on the suction surface boundary layer moves forward with increased mainstream turbulence intensity and Reynolds number. The heat transfer coefficient augmentations and peak values on the suction and pressure surfaces are affected by the mainstream turbulence and Reynolds number.