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The present study conducts an experimental investigation into the flow characteristics over a cascade of both slotted and non-slotted compressor blades. The focus is on evaluating potential statistical correlations between higher-order moments of velocity fluctuations, including Skewness and Kurtosis. The linear axial cascade comprises three NACA6409 blades, which are tested in both normal and slotted blade. Data acquisition was conducted using a hot wire anemometer at three measurement stations within the cascade. The hot wire sensor was positioned at distances of x/c = 0.125, 0.25, and 0.5 from the trailing edge (x), where x represents the distance from the probe to the trailing edge of the airfoil and (c) is the chord length of the blade. Measurements were taken at a blade angle of attack of 0° and two Reynolds numbers: 22,750 and 45,500. Results indicate that blade grooving enhances flow velocity, postpones separation and improves flow control in the trailing edge region. By comparing calculated Skewness and Kurtosis values with those predicted by existing boundary layer and free jet relations, more consistent correlations were identified. To provide more accurate relationships, two polynomials of the second and third order have been used. It was found that high-order values of velocity were obtained more accurately with the relations presented in this research. Although the accuracy of these predictions is significantly reduced in the proportion of larger distances. In distant stations, the loss velocity has decreased. As the distance from the model increases, the amount of inhomogeneities in the sequence increases and the values of the opposite Skewness become zero. Turbulence intensity has been reduced by slotting the blades. [ABSTRACT FROM AUTHOR]

This experimental investigation aims to analyze the heat transfer capabilities of both single and multi-orifice SJs (MOSJs) for varied waveforms(sine, square, and triangular), at a fixed Reynolds number (3525). The jet-to-plate distance and pitch radius is varied in the range of 1–19 and 3.8–8 mm, respectively. The MOSJs at pitch radius (PR) of 3.8 mm shows 30.6% higher average Nusselt number than single SJs. For a PR of 8 mm, the Nusselt number contour shows multiple heat transfer regions adjacent to the stagnation point; however, a single heat transfer region is evident at PR of 3.8–6 mm. [ABSTRACT FROM AUTHOR]

We have developed a new method for measuring temperature and velocity at a high spatial resolution (minimum 2.56 mm pitch along an optical fiber). The developed method uses the same principle as a hot wire anemometer, where the velocity perpendicular to an optical fiber is estimated as a function of the cooling curve of a gold-coated layer on the optical fiber Joule-heated intermittently. The developed optical fiber sensor demonstrated the ability to acquire a transient velocity profile in airflow experiments with high repeatability and accuracy. This paper describes optical fiber-based velocity measurement in the velocity range of approximately 0–7 m/s with an error of approximately 10% compared to a hot wire anemometer and a new method for simultaneous temperature and velocity measurements. Applicability to velocity distribution measurements and seconds transient velocity changes are also described. [ABSTRACT FROM AUTHOR]

Single mode-Multimode-Single mode (SMS) sensors have been attracted a relevant attention because of their simple manufacturing, their capability of sensing different quantities, and their enhanced sensitivity compared to the most common fiber optic sensor represented by Fiber Bragg Gratings (FBGs). Moreover, SMS sensors exhibit blue-shift sensitivity to strain, opposite to FBGs, making them suitable in applications where strain-temperature cross-sensitivity may be an issue. SMS sensors are made by splicing a short multimode, preferably a two mode or quasi two-mode, optical fiber jumper between single mode pigtails. The interference of the modes propagating at different phase velocities produces a spectral pattern that shifts with temperature, strain or any perturbation of the phase difference among the modes. In this paper we review the main features of SMSs as temperature sensors and we present a potential biomedical application in an all-fiber flowmeter based on the hot-wire principle: a fiber-coupled laser source at 980 nm is used as a controllable heating source of the SMS sensor that, when immersed in fluid flow, converts the temperature variation, caused by the heat removal, into a wavelength shift of the transmitted spectrum. Thermal characterization and proof-of-concept experiments show the feasibility and functionality of the sensor and provide an outlook on possible developments and potential applications. [ABSTRACT FROM AUTHOR]

Single mode-Multimode-Single mode (SMS) sensors have been attracted a relevant attention because of their simple manufacturing, their capability of sensing different quantities, and their enhanced sensitivity compared to the most common fiber optic sensor represented by Fiber Bragg Gratings (FBGs). Moreover, SMS sensors exhibit blue-shift sensitivity to strain, opposite to FBGs, making them suitable in applications where strain-temperature cross-sensitivity may be an issue. SMS sensors are made by splicing a short multimode, preferably a two mode or quasi two-mode, optical fiber jumper between single mode pigtails. The interference of the modes propagating at different phase velocities produces a spectral pattern that shifts with temperature, strain or any perturbation of the phase difference among the modes. In this paper we review the main features of SMSs as temperature sensors and we present a potential biomedical application in an all-fiber flowmeter based on the hot-wire principle: a fiber-coupled laser source at 980 nm is used as a controllable heating source of the SMS sensor that, when immersed in fluid flow, converts the temperature variation, caused by the heat removal, into a wavelength shift of the transmitted spectrum. Thermal characterization and proof-of-concept experiments show the feasibility and functionality of the sensor and provide an outlook on possible developments and potential applications.

The effect of initial conditions in a 200 mm × 1000 mm × 400 mm sidewall enclosure on the mean flow characteristics of a three dimensional turbulent square wall jet has been studied experimentally. The initial conditions are varied by varying the length of the nozzle; it is varied as l / h = 10, 50, and 90, where l and h indicates the nozzle length and the side of the square nozzle, respectively. The effect of nozzle length on initial velocity profiles, velocity distribution in lateral and wall normal directions, spread rate, decay of maximum mean velocity, local Reynolds number and similarity behaviour has been studied. The wall normal spread width is higher for the nozzle length l/h = 10 in the near field (x / h ≤ 10) but this trend completely changed after x / h ≥ 10. The spread rate is found independent of the initial condition of the nozzles in the fully developed region. The decay rate of maximum mean velocity is found higher for l / h = 10 in the region of (5 ≤ x / h ≤ 25) , whereas decay rate becomes independent of the initial conditions in the fully developed region (x / h ≥ 25) . The local Reynolds number variation is also estimated along the downstream directions for present case and found that the local Reynolds number (R e x) reaches approximately 56% of the jet exit Reynolds number (R e jet ) at x / h = 40 for nozzle length l / h = 10, while it is 57% and 59% of Rejet for the nozzles l / h = 50 and l / h = 90 respectively at the same location. The nozzle l / h = 10 attained self similar behaviour more quickly as compared to the other nozzles. The sidewall played a significant role which pushed the fluid more towards the center resulting in a lower jet half width in the wall normal direction as compared to the corresponding case, without a sidewall. The decay rates of the maximum mean velocity for all the nozzles are estimated to be 1.08 which is in the accepted range found in the literature. [ABSTRACT FROM AUTHOR]

In two-dimensional measurements using hot wire anemometer, the sensitivity of the sensor to change the flow direction (sensitivity of direction or angular response of sensor) is of particular importance. Sensitivity of direction of sensor, relation between flow velocity vector and heat transfer from the hot wire sensor is determined, using the Yaw sensitivity function and its coefficient. In some cases, negative values of Yaw sensitivity coefficient k^2 are encountered, for which no specific reason has been presented. In this paper, reason of negative values of k^2 for un-plated sensors of hot wire anemometer in two-dimensional measurements have been investigated experimentally. For this purpose, flow velocity field between the prongs of a model of a normal probe (SN) at different velocities and Yaw angles have been studied. Results show that the probe’s prongs produce flow disturbances, which cause a reduction in flow velocity and the deviation (rotation) of the flow adjacent to the prongs and the sensor. At different Yaw angles, the maximum reduction in flow velocity amounts to 3% and the deviation of flow direction has a maximum of 6.3°. It is supposed that this phenomenon affects the amount of heat transfer from the sensor and the effective velocity obtained by the hot wire anemometer, which eventually produces the reported negative k2 values. [ABSTRACT FROM AUTHOR]

This paper presents a short response time, all-silica, gas-flow-velocity sensor. The active section of the sensor consists of a 16 µm diameter, highly optically absorbing micro-wire, which is heated remotely by a 980 nm light source. The heated microwire forms a Fabry–Perot interferometer whose temperature is observed at standard telecom wavelengths (1550 nm). The short response time of the sensor allows for different interrogation approaches. Direct measurement of the sensor’s thermal time constant allowed for flow-velocity measurements independent of the absolute heating power delivered to the sensor. This measurement approach also resulted in a simple and cost-efficient interrogation system, which utilized only a few telecom components. The sensor’s short response time, furthermore, allowed for dynamic flow sensing (including turbulence detection). The sensor’s bandwidth was measured experimentally and proved to be in the range of around 22 Hz at low flow velocities. Using time constant measurement, we achieved a flow-velocity resolution up to 0.006 m/s at lower flow velocities, while the resolution in the constant power configuration was better than 0.003 m/s at low flow velocities. The sensing system is constructed around standard telecommunication optoelectronic components, and thus suitable for a wide range of applications.

The air-flow field of the circumferentially arranged nozzle group is modeled and simulated. The air velocity distribution is measured using a hot wire anemometer. The results show that the simulated velocities coincide with the measured ones, confirming the effectiveness of the model. Larger rotating speeds can yield larger air velocities, indicating that introducing auxiliary air is favorable to the polymer drawing in the centrifugal spinning. [ABSTRACT FROM AUTHOR]

In two-dimensional flow measurement using hot wire anemometer, directional sensitivity (angular response) of sensor plays an important role in the measurement accuracy. The angular response of the sensor describes the relationship between flow velocity vector and heat transfer from the sensor, which is determined by a sensitivity function. In this paper, two sensitivity functions, namely cosine law and Hinze equation, have been studied using wind tunnel experiments to evaluate the effect of various parameters such as flow conditions (velocity and direction), probe aspect ratio (l/d) and probe operational condition (sensor temperature) on the range of applicability of cosine law and magnitude of the sensitivity coefficient, k. Results show that the angular range of applicability of cosine law depends on flow and probe conditions. At 1% measurement error, the range of applicability of cosine law for flow measurements of velocities exceeding 10 m/s was found to be in the range of ±30º. Moreover, at geometrical ratios higher than 600, two-dimensional flow measurements using the cosine law presents results with acceptable accuracy. In addition, the sensitivity coefficient is completely dependent on flow condition and probe aspect ratio, and its value decreases with increase in flow angle and velocity and reduction in probe aspect ratio. The results of this research can be used in the selection and proper design of probes for two-dimensional flow measurements using hot wire anemometers. [ABSTRACT FROM AUTHOR]

• The local gas velocities are higher in the near-wall region of the PBR core. • The flow of the gas follows the path of the last resistance that is near the wall. • The gas velocity variation in the PBR is due to the variation of void fractions. • The gas velocity in the PBR varies in same trend as heat transfer coefficients. Obtaining accurate results and new benchmark data for the local velocity of the gas flowing within the pebble bed reactor (PBR) is a key step for understanding and benchmarking simulations of the thermal hydraulics in the PBR core as it significantly affects the design and safety operation of these reactors. Therefore, this work focused on studying the local gas velocities inside a pebble bed using a sophisticated hot wire anemometry (HWA) technique, which was supported with a novel probe-protector case that protected the probe, allowing the measurements to be conducted at various locations in a pebble bed with pebble diameter of 5 c m and an aspect ratio of 6. The measurements were conducted at various superficial inlet gas velocities (0.3 ≤ U g ≤ 2.4 m / s) , covering both transitional and turbulent flow conditions (993.78 ≤ R e ≤ 7950.24) at three axial levels and four radial locations (r / R = 0 , 0.33 , 0.67 , 0.9). The results highlighted the effect of the wall on the variation of the local gas velocities inside the pebble bed, as higher gas velocities were recorded at the near-wall region, where the void fractions are higher, providing a path of the least resistance to the flow of the gas, compared to the center of the bed. Furthermore, a second order polynomial correlation with an R 2 = 93.96 % and an AARE equal to 1.47 % was developed for the prediction of the local gas velocity inside the bed, within the experimental range of the study. The accurate gas velocity measurements obtained in this study can serve as benchmark data for the validation of CFD simulations coupled with heat transfer calculations. [ABSTRACT FROM AUTHOR]

The pulsating heated flows are traditionally a difficult subject to treat with conventional hot wire or film methods. Special factors that complicate matters are flow reversal and non linear flow effects of vortices and wire probe wake disturbances on the heat transfer to the hot film or wire sensor in heated pulsating flows. The presence of these strongly nonlinear and unknown terms leads to great difficulties in calibration of hot film probes in this particular regime. The paper analyses the current state of matters in the field and reports a series of solutions that have been practically tested in a case of a high speed pulsated heated flow. Normally such measurements are made in a non-contact fashion using a LDV system or various visualization techniques but there have been recent attempts to use a constant temperature hot wire anemometer system (CTA).To obtain meaningful calibration for hot wire films in hot pulsating flows, a comparison system on other principles (LDV) was used, as well as a specially designed nozzle to replace the calibrator unit that could not be operated with heated fluid due to structural integrity reasons. The method as described below works well for the expected speed range that could be generated using the special nozzle.

Measuring and modeling flow has played a central role in predicting its behavior and its effects on the surroundings. Flow measurement is the basis of trade between producers, transporters, process plants, state and public marketers. To improve transactional operation, thermal flowmeters could provide direct mass flow measurement of gases and vapors over a wide range of process conditions without the need for density corrections based on pressure and temperature. The flow meters are classified according to the domain in which they are used and their operating principle. The goal of this work is to provide an overview of using thermal flow meter in hydrocarbons industries. The applicability of thermal flow meters is discussed by a simulation using one-dimensional mathematical model of thermal flow sensor. [ABSTRACT FROM AUTHOR]

Experimental investigation of the effect of flow turbulence on the steady state burning of methanol is reported. A vertical air tunnel has been mounted with a grid at its exit plane in order to generate turbulence in the free jet stream. The flow field has been characterized using a hot-wire anemometer. Mean and fluctuating flow velocities and integral scale have been measured at an axial location of around 2 times its exit diameter ( D ). Three types of grids have been used. Classical porous sphere experiments have been carried out to analyze the steady-state burning rate of methanol over the surface of an inert sphere having constant diameter. Experiments have been done at atmospheric pressure under ambient temperature and normal gravity conditions. A porous sphere is positioned at an axial location of 2 D , where the approaching flow has been characterized in detail. Results show that the burning rate as well as the flame stability are greatly influenced by the free stream turbulence. The ratio of turbulent time scales and the chemical time scales for grid mounted cases have been estimated from the integral scale, root mean square velocity fluctuation, flame stand-off distance and the vapor blowing velocity. Empirical expression relating the normalized burning rates to diffusion scale based Damköhlar number has been presented. A correlation for Sherwood number as a function of Reynolds number and turbulent intensity has also been proposed. [ABSTRACT FROM AUTHOR]

In this paper we present a novel complete anemometric electronic system based on an array of hot wire sensors, provided by Telecontrolli SME, and a suitable heater feedback that achieves, thanks to a dedicated algorithm, a CMOS integrable portable solution showing a robust design, without moving parts and small dimensions. The sensor interface is implemented by means of a modified Wheatstone bridge architecture with autobalancing capability. Comparisons with a commercial cup anemometer have shown that the proposed architecture, with reduced space occupancy and low power consumption, is suitable to operate in a natural environment in the −20 to +55 °C temperature range providing wind speed and direction measurement. Concerning the wind speed, a 0.6 m/s sensitivity has been achieved. The integrated CMOS design of the final system is also presented and discussed in the paper. [ABSTRACT FROM AUTHOR]

In this paper, due to the importance of incoming flow turbulence intensity into combustion chamber, tripping wire effect on the flow wake has been experimentally investigated within a linear compressor cascade. Besides, effects of changes in the attack angle of compressor blades on the characteristics of wake are investigated. Investigation on the velocity, turbulence intensity and vortex frequency in the wake of blade in the attack angles of -10, 0 and 10 is done. In previous work the effects of a smaller angle of attack has been examined [1]. Therefore, to better understand the flow in the wake, more essential investigations appeared to be necessary for more angles of attack. Thus, two wires were implemented along each blade and their effects on average velocity, turbulence intensity and vortices frequencies were accurately considered. Increasing the angle of attack, leads to increase in the domain of wake and frequency at maximum amplitude, and the maximum Strouhal number. To do this, single channel hot wire anemometer was used to measure the wake parameters. [ABSTRACT FROM AUTHOR]

The pulsating heated flows are traditionally a difficult subject to treat with conventional hot wire or film methods. Special factors that complicate matters are flow reversal and non linear flow effects of vortices and wire probe wake disturbances on the heat transfer to the hot film or wire sensor in heated pulsating flows. The presence of these strongly nonlinear and unknown terms leads to great difficulties in calibration of hot film probes in this particular regime. The paper analyses the current state of matters in the field and reports a series of solutions that have been practically tested in a case of a high speed pulsated heated flow. Normally such measurements are made in a non-contact fashion using a LDV system or various visualization techniques but there have been recent attempts to use a constant temperature hot wire anemometer system (CTA).To obtain meaningful calibration for hot wire films in hot pulsating flows, a comparison system on other principles (LDV) was used, as well as a specially designed nozzle to replace the calibrator unit that could not be operated with heated fluid due to structural integrity reasons. The method as described below works well for the expected speed range that could be generated using the special nozzle. [ABSTRACT FROM AUTHOR]

Natural dry draft cooling towers are one of the most popular types of towers in power plants that are being used in dry climate areas. One problem with this type of tower is the impact of environmental factors on their performance. Wind is one of these factors. Wind develops a phenomenon called wind cover that prevents outgoing gasses from escaping. In this work, the effects of wind on flux and distribution of output velocity in tower outlet is studied by using wind tunnel and hot wire anemometer. Also the effects of wind break walls are studied with respect to hampering these effects. [ABSTRACT FROM AUTHOR]

Abstract: There is a great need for a low cost and low power consumption portable spirometer for the home care of respiratory diseases. A mobile monitoring system utilizing Bluetooth and mobile messaging services (SMS) with low-cost hardware equipment is proposed. A proof of concept prototype has been developed and implemented to enable transmission of a flow or volume of gas during inspiratory and expiratory process signal of a patient, which can be expanded to include other vital signs. Communication between a mobile smart-phone and the spirometer is implemented using the popular personal area network standard specification Bluetooth. We used SMS for transmission, the mobile phone plots the received signal and displays the flow measurement application software running on the client mobile phone itself, where the plot can be captured and saved as an image before transmission. The acquired signal is transmitted via the Bluetooth to the processing and diagnostic unit with wireless protocol between sensors and the electronics board. The flow measurement is done with a silicon hot wire anemometer manufactured with MEMS technology. The design, manufacturing, calibration, and basic characterization of MEMS hot-wire anemometer and digital spiromerter is presented. [Copyright &y& Elsevier]

This paper presents an experimental investigation of the influence of a transversal flow deflector on the cooling of a heated block mounted on a flat plate. The deflector is inclined and therefore it guides the air flow to the upper surface of the block. This configuration is simulating the air-cooling of a rectangular integrated circuit or a current converter mounted on an electronic card. The electronic component is assumed dissipating low heat power, as such, air forced convection is still a sufficient cooling way even without fan or heat sink on the component. The measurements are given by hot and cold wires anemometers and by an InfraRed camera. The results give details of the effects of the deflection on the hydrodynamic and the thermal fields on and over the block for different inclination angles. They show that the deviation caused by the deflector may significantly enhance the heat transfer from the component. Deflection is also able to avoid local overheating of the electronic component. Optimum heat transfer rate and homogenised temperature are shown to be obtained with an inclination angle α=30°. [ABSTRACT FROM AUTHOR]

In this article, a novel combustor for stable, high efficiency, and low pollution combustion of mixture of purge gas and crude gas is proposed; experiments and numerical simulation were undertaken. Hot wire anemometer was employed to investigate the velocity profiles and some detailed flowing characteristics were studied by using a numerical simulation method. The results of the experiments and simulation agreed well, and an obvious recirculation region was found downstream from the secondary air distributors. The recirculation rate could be adjusted conveniently. Configuration parameters of secondary air distributors were optimized and better flow fields were achieved. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the performance of five well-known turbulence models, in order to find a model that predicts the details of the flow patterns through an electromagnetic compatibility (EMC) screen. The turbulence models investigated in the present study are five different eddy-viscosity models; the standard k-ϵ model, the renormalization group (RNG) k-ϵ model, the realizable k-ϵ model, the standard k-ω model, as well as the shear stress transport k-ω model. A steady-state 3-D detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible. A general model that covers a considerable range of velocities and geometries was validated experimentally by wind tunnel measurements. The result shows that for most of the k-ϵ models used with correct y+ and mesh strategy, the pressure drop and the velocity field deviation is small compared to experimental data. The k-ω models overpredict the overall pressure drop. When using the RNG k -ϵ model, the total static pressure drop predicted differs around 5%-10% and the average velocity deviation at several locations before and after the screen is around 5%. [ABSTRACT FROM AUTHOR]

A delay based artificial neural network is used to analyze turbulent flow signals obtained by a hot wire anemometer along time in different points within the wake of a circular cylinder. Values of the Reynolds number range from 2000 to 8000, corresponding to late transitional or fully turbulent wake flows. The implemented trainable delay based artificial neural network is able to autonomously obtain the embedding dimension as well as the normalized embedding delay and permits performing short and long term predictions. The short term predictions are extremely accurate while the long term ones result in a sort of nonlinear filter able to extract the signal features concerned with the larger eddies and coherent structures present in the turbulent flow-field. [Copyright &y& Elsevier]

Measurements of mean and fluctuating velocity and temperature and their self- and cross-products to the third-order are presented for a heated axisymmetric air jet. Froude numbers in the range of 3500–13,190, Reynolds numbers in the range of 3470–8500 and non-dimensional streamwise distances, X*, from 0.27 to 1.98 are covered by the data. It was found that turbulence intensity decreases for the heated jet in the region between the inertia dominated and the buoyancy dominated regions which is contrary to findings with helium jets mixing with ambient air to produce density fluctuations. The effects of heating on the turbulent kinetic energy budget and the temperature variance budget show small differences for the inertia dominated region and the intermediate region which help to explain the transition process to the far field plume region. Constants are evaluated for the isotropic eddy diffusivity and generalised gradient hypothesis models as well as the scalar variance model. No significant effect of heating on the dissipation time-scale ratio was found. A novel wire array with an inclined cold wire was used. Measurements obtained with this probe are found to lead to asymmetries in some of the higher-order products. Further investigation suggested that the asymmetries are attributable to an as yet unreported interference effect produced by the leading prong of the inclined temperature wire. The effect may also have implications for inclined velocity wires which contain a temperature component when used in heated flows. [Copyright &y& Elsevier]

This paper presents a short response time, all-silica, gas-flow-velocity sensor. The active section of the sensor consists of a 16 µm diameter, highly optically absorbing micro-wire, which is heated remotely by a 980 nm light source. The heated microwire forms a Fabry–Perot interferometer whose temperature is observed at standard telecom wavelengths (1550 nm). The short response time of the sensor allows for different interrogation approaches. Direct measurement of the sensor's thermal time constant allowed for flow-velocity measurements independent of the absolute heating power delivered to the sensor. This measurement approach also resulted in a simple and cost-efficient interrogation system, which utilized only a few telecom components. The sensor's short response time, furthermore, allowed for dynamic flow sensing (including turbulence detection). The sensor's bandwidth was measured experimentally and proved to be in the range of around 22 Hz at low flow velocities. Using time constant measurement, we achieved a flow-velocity resolution up to 0.006 m/s at lower flow velocities, while the resolution in the constant power configuration was better than 0.003 m/s at low flow velocities. The sensing system is constructed around standard telecommunication optoelectronic components, and thus suitable for a wide range of applications. [ABSTRACT FROM AUTHOR]