Impact of the Confinement Plate on the Velocity of Synthetic Jet

In the paper, the impact of the limitation of the environment around the office of synthetic jet actuators were tested. One short and three length orifices were tested and compared with and without confinement plate. In total, seven different synthetic jet actuators were investigated. The constant temperature anemometer was used for the velocity measurements. The synthetic jet was tested for the Reynolds number in the range of 2300 < Re < 19,500, and the Stokes number in the range of 46 < S < 62. The confinement plate decreased the velocity of synthetic jet depending on the actuator supply power even around 5%. However, the differences in axial velocity profile are slight and the impact of the confinement plate was visible only in the distance x/d < 4.

Constant-Temperature Anemometer Bandwidth Shape Determination for Energy Spectrum Study of Turbulent Flows

Due to their common occurrence and fundamental role in human-realized processes and natural phenomena, turbulent flows are subject to constant research. One of the research tools used in these studies are hot-wire anemometers. These instruments allow for measurements in turbulent flows in a wide range of both velocities and frequencies of fluctuations. This article describes a new indirect method of determining the bandwidth shape of a constant-temperature anemometer. The knowledge of this bandwidth is an important factor in the study of the energy spectrum of turbulent flows.

Retraction: Nebhen, J., et al. Constant Temperature Anemometer with Self-Calibration Closed Loop Circuit. Appl. Sci. 2020, 10, 3405

In the published paper [...]

Constant Temperature Anemometer with Self-Calibration Closed Loop Circuit

In this paper, a Micro-Electro-Mechanical Systems (MEMS) calorimetric sensor with its measurement electronics is designed, fabricated, and tested. The idea is to apply a configurable voltage to the sensitive resistor and measure the current flowing through the heating resistor using a current mirror controlled by an analog feedback loop. In order to cancel the offset and errors of the amplifier, the constant temperature anemometer (CTA) circuit is periodically calibrated. This technique improves the accuracy of the measurement and allows high sensitivity and high bandwidth frequency. The CTA circuit is implemented in a CMOS FD-SOI 28 nm technology. The supply voltage is 1.2 V while the core area is 0.266 mm2. Experimental results demonstrate the feasibility of the MEMS calorimetric sensor for measuring airflow rate. The developed MEMS calorimetric sensor shows a maximum normalized sensitivity of 117 mV/(m/s)/mW with respect to the input heating power and a wide dynamic flow range of 0–26 m/s. The high sensitivity and wide dynamic range achieved by our MEMS flow sensor enable its deployment as a promising sensing node for direct wall shear stress measurement applications.

Experimental study of aerodynamic loads on ground-mounted solar panel arrays: The panel spacing and inclination angle effect

The influence of panel inclination, wind direction, and longitudinal panel spacing on the wind loads of the model of ground-mounted solar panel arrays scaled 1:20 in a wind tunnel was investigated for a Reynolds number of 1.3 × 105. The experiments were carried out at the panel inclination of 25° and 45°, dimensionless panel spacing in tandem of 0.5 and 1, and the wind directions of the incoming flow were varied from 0° to 180° at 30° intervals. A constant temperature anemometer was used to measure the velocity and turbulence intensities, and a pressure scanner system measured static pressures. The results indicated that the net pressure coefficients of the solar panels were increased with the panel inclination angle and spacing between solar panels, and the maximum wind loads were obtained on the first windward panel. It was also observed that in terms of maximum uplift and drag, 180° and 0° was found to be the critical wind direction, respectively. In contrast, in terms of overturning moments, 30° and 150° were the critical wind directions.

Experimental study of weak shock waves influence on the supersonic boundary layer of the flat plate model

The experimental study of the effect of weak shock waves on the supersonic boundary layer of the flat plate with a blunt leading edge (the radius of bluntness was r = 2.5 mm) with Mach number M = 2.5 and zero angle of attack was carried out. The measurements were carried out using the constant temperature anemometer. The paper presents a complex flow structure on the surface of the model. High-intensity peaks were found in the regions of the disturbed flow. Also the spectral analysis of perturbations was performed. It is found that the supersonic boundary layer on a flat plate is very sensitive to the effect of weak shock waves.

Mapping of the turbulent round jet developing region using a constant temperature anemometer (CTA)

The fully developed round turbulent jet has been extensively studied, whereas the developing region is much less understood. The high shear and turbulence intensities in the most interesting parts of the developing region make them inaccessible to common measurement techniques such as Constant Temperature Anemometry (CTA) due to the high demands on the measurement techniques for accuracy of the measurements. Turbulence measurements are therefore planned using our in-house laser Doppler anemometer (LDA) system based on its capability to provide accurate measurements and with its inherent ability to properly distinguish velocity components. A rigorous measurement with the intended LDA system however demands impractical processing time, so knowing the critical points at which measurement are to be taken will save valuable time. This information is herein acquired significantly faster and more practically, however less accurately, with single-wire CTA. A high-resolution measurement was done using a computer-controlled single-wire CTA with the wire probe mounted perpendicular to the incoming flow from the jet orifice. The measurements covered several points in the radial (r-direction) along x/D=10, x/D=15, x/D=20 and x/D=30 downstream (where D is the jet exit diameter), with spatial resolutions ranging from 1 to 3 mm between the points, depending on how far the measurement was from the jet centerline. A proper alignment was also conducted prior to measurement so that the same points can be reached again for LDA measurement on the same jet afterwards. The radial profiles of mean velocity and turbulence intensity at each downstream position are presented to show the statistics of the air flow inside and outside the jet. As expected from theory, the mean profiles display a nearly Gaussian shape, spread out and tapered with the downstream direction. The highest velocities are located at the centerline.

Calibration of a Wall-Shear-Stress Sensor Made of a Flush-Mounted Hot-Wire Over a Shallow Rectangular Slot

The design, construction, and calibration of a wall-shear-stress sensor (WSSS) made of a flush-mounted hot-wire over a shallow rectangular slot are described. The rectangular slot beneath the hot-wire reduces the heat loss to the substrate and enhances the frequency response of the WSSS. The WSSS was connected to a constant-temperature anemometer (CTA) and calibrated by making measurements in fully developed flows of air in a parallel-plate channel, at three different channel heights. Initially, the square of the time-averaged voltage supplied to the hot-wire by the CTA was plotted against the time-averaged wall-shear-stress. With this practice, however, for a fixed value of the overheat ratio, even relatively small fluctuations of the ambient air temperature produced a fair amount of scatter in the calibration data, and this adverse effect was compounded by minor drifts in the electrical resistance of the hot-wire (unheated value) over the course of the measurements. For overcoming this difficulty, an alternative practice for correlating the calibration data was proposed and successfully implemented. The details of this WSSS, the proposed novel calibration practice for the WSSS, and related results are presented and discussed in this paper.