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.

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. 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 toincrease inthe 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.

In this research, turbulence parameters such as turbulence intensity, Kolmogorov length scale, dissipation rate and velocity profiles at a cross section of flow over a flat plate are analyzed by using Hot Wire Anemometer. Furthermore, the behaviors of parameters at unknown heights of plate are predicted by utility of advanced neural networks. One can find that there is well agreement between results of neural network at unidentified points and experimental data that guaranties the use of neural network to determine turbulent parameters at each point that there are not any experimental data for them. In addition to, frequency analysis and the effect of number of samples on the turbulence parameters are considered. The results show that the turbulence intensity, Kolmogorov length scale and Kurtosis are decreased with increase the height where dissipation rate and mean velocity are increased. Furthermore, the amplitude of FFT is increased near the plate.

Engine cooling system plays a major role in performance of vehicle engine, in which the radiator and the fan are the main components. In this article, the performance of two fans with different characteristics has been appraised within an engine cooling system. For this purpose, performance characteristics curves of both fans, including, static pressure and total pressure against flow rate have been generated. Then a test rig, similar to that of an engine's cooling system, was set up for the fan and the radiator. Subsequently the air flow rate and Radiator's inlet flow distribution have been measured precisely under working conditions using Hot Wire Anemometer. also, the inlet airflow pattern was analyzed. Results reveal that intersection point of the system resistance curve and static pressure curve of the fans, do not represent the actual and true values of flow rate of the fans. However the actual flow rate is less than those anticipated. Then, some modifications were made to the entrance of one of the fans and it's shroud, and similar tests have been performed. Although the test results after modification showed more uniformity in the flow towards the radiator, the increase of flow rate was minimal in the cooling system. Also, road tests of the vehicle did not represent much improvement on the performance of the cooling system.

Efficient design of radiator is of paramount importance in the performance of an automotive cooling system. In this paper, two radiators with different characteristics have been tested, and their behavior appraised. For this purpose, system resistance curves for both radiators have been plotted. Characteristic curves of fans, including the static and total pressure against the flow rate, were plotted and operating points for each radiator determined. Then a test rig, similar to that of an engine's cooling system, was set up for the fan and the radiator. Radiator's inlet flow distribution was precisely measured, using Hot Wire anemometry, and the inlet airflow pattern was analyzed. A comparison of results reperesents that 15% increase in the number of the blades in unit length can increase pressure drop in radiator and therfore, the air flow rate decreases by 9% at the speed of 2800 r.p.m. However, due to the increase in the heat transfer area, the thermal performance of the radiator has improved and the heat transfer rate has increased by 11%. Road tests on the vehicles also show this improvement in the performance of the cooling system.

In the present research work, flow behavior in a centrifugal compressor has been experimentally investigated at various operating conditions from far to near surge and different compressor rotational speeds. Having introduced the experimental set-ups, results of velocity fluctuations at compressor inlet, as a surge precursor, have been presented. Hot-Wire anemometry of high frequency response was used to measure these fluctuations at three compressor rotational speeds of 9000, 10000 and 13000 rpm and three operating conditions of maximum flow coefficient, near design point and surge conditions. Experimental results showed that reduction from maximum flow coefficient towards the surge point can increase fluctuations of instantaneous velocity signals at aforementioned rotational speeds by the factor of 2. 6, 1. 9 and 1. 57, respectively. In addition, increase of compressor rotational speed increases fluctuation of instantaneous velocity signals at surge condition by an average factor of 1. 17. Finally, analysis of frequency spectrums of velocity fluctuations, showed a dominant frequency of surge at about 30 percent of the blade passing frequency.

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.

Hot Wire Anemometer (CTA) can be used to measure instantaneous flow velocity with high frequency. Since the principle of opearation of CTA is based on convective cooling, determination of the air flow direction is difficult. In this Research paper, we have used two cylindrical Hot-film sensors placed in parallel to determine the flow direction. The wake effect and the heat due to the upstream sensor on the downstream sensor has been used to identify the flow direction. Effect of wake and presence of the upstream sensor on the downstream sensor has been studied. The results have been used to construct a probe consisting of two parallel sensors, sepereated by 1mm distance. Performance of the probe has been evaluated at various flow angles for laminar and turbulant flows. Findings of this study show that this probe provides the best performance at±10o flow angles.

In this research, the effects of LEX angle on flow pattern over the diamond wing by using Hot-Wire and five-hole probe are investigated. The pressure coefficient tests over the wing at three different angles of attack respectively 5, 10 and 15 degrees and on two section was conducted by five hole probe. Also turbulence intensity measurements were conducted at three sections for 10 degree angle of attack by using Hot Wire Anemometer. Experimental tests were conducted in a closed circuit wind tunnel with acceptable flow quality at the velocity of 12.5 (m/s) equal to 192500 Reynolds number. At a constant angle of attack with a downward movement the flow; the vortex diameter formed due to the Leading edge of the wing. Therfore, the LEX vortex increased which has led to growing pressure suction on the wing. Amplified suction pressure at the center of the LEX vortex core and the leading edge vortex have carried the two vortices closer together. Thus, the larger the vortex core lead to higher turbulence intensity by moving to downstream. Frequency analysis near the center of the leading edge vortex and Lex vortex showed that at constant section over the wing, the turbulence intensity near vortex core exposed, increasing turbulence intensity that caused to rise the amplitude spectra of fluctuation. Furthermore, frequency analysis indicate that the maximum domain of power spectra increases for LEX angle of 16 degree with rising of angles of attack.

The dynamics of a vertical two-dimensional air jet under acoustic excitations at a low Reynolds number are investigated experimentally. The perturbation is introduced by means of a loudspeaker located in a settling chamber before the nozzle exit. The experiments are operated at Strouhal number St ranging from 0 to 1 and for different pulsation amplitudes. A laser plan is used to visualize the flow and the Hot-Wire anemometry for more specific measures of the mean and fluctuation velocity. The discussion is focused on the influence of two parameters governing the flow: the Strouhal number St and pulsing amplitude. The main results show that the flow consisting of the vortex propagating downstream a nozzle exit is strongly affected by the excitation. Indeed, the introduction of an external perturbation introduces a more rapid degeneration of the potential core with the appearance of vortices near the nozzle as the pulsation amplitude increases. These vortices are amplified and become larger than the nozzle width which induces the enhancing of the entrainment and mixing effects of the shear layers. Another very important phenomenon is observed: the excitation has led to the formation of a switching from the asymmetric mode (sinuous mode) to the symmetric mode (varicose mode).