جستجوی مقالات مرتبط با کلیدواژه « Skewness » در نشریات گروه « مکانیک »

In this study,flow dynamicsand accelerated flow effects on the various parameters of the wakeof a bluff body model Such as Skewness, Kurtosis and Kolmogorov scale length, investigated experimentally. In addition, the effects of acceleration in the rate and trend of variation of the various parameters of the wake studied. The blow open circuit wind tunnel used to simulate fluid flow. An inverter that causes the changes in rotational speed of the wind tunnels electro motor has increased the inlet wind velocity continuously. On all wake positions, flow Accelerate and Increasing velocity creates smaller sized vortices. The passage of time and the increase in velocity do not have any effect on the changes of the skewness and kurtusis parameters in the near wake. By increasing the velocity, the values of the Kolmogorov scale length reduced generally. also; the values of the parameter in the far wake are greater than the close wake. There is a greater energy dissipation in the parts of the wake where the effects of the shear layers are and this causes smaller sized vortices

Abstract: In spite of the fact that turbulence is one of the very old issues in the domain of fluid mechanics, it has been remained unresolved. In this paper is done the experimental investigated on the flow dynamics and the high-order parameters such as Flatness and skewness of wake of vehicle model also is shown The Frequency variations vortex formation at the maximum amplitude, strohal Number and Length scale Incorporation. All testing was performed aerodynamic Hakim Sabzevari University To measure the flow characteristics, the wind tunnel and a hot wire flow meter Made by Saba Frasnjsh is used. The maximum disturbances and nominal maximum speed of the device, respectively are, 0. 1% and 30 m / s. The results showed: Skewness values at lower altitudes are less than its values at higher altitudes that it has a reverse trend with increasing distance from the vehicle. Flatness values gradually decreased with increasing distance from the vehicle. The strohal number is often reduced by increasing the distance between car and trailer. And mixing length scale within the wake often has one or two maximum peaks. The wake of Trailer for near car locations to the trailer dosent have any Effect on the formation of the maximum peak is mixing length scale.

In this paper, the existence of statistical relationship between high- order velocity moments as flatness and skewness in the plain wake behind a circular cylinder were studied. Hot- wire anemometer was used to measure turbulent parameters in various situations downstream the flow behind the cylinder. Turbulence intensity of wind tunnel’s free line is 0.1 precent which in this sense, it has high accuracy. In these experiments, the Reynolds number is 28000. Non- dimensional values of mean velocity, skewness S and flatness F in various x/d’s has been plotted. By comparing existent relationship for predicting flatness values (which are demonstrated for turbulent boundary layer and free jet) with actual values, it has been found that new relationship can be found which can have much more agreement with their actual cases. Considering this point, and by using fitting method, in this paper some new relationship from which was can predict high- order moments with much more accuracy was provided. Therefore for further accuracy, two polynomial of orders 2 and 3 were used to fit the data which has taken in a wind tunnel. Though the accuracy of these estimations in larger x/d’s reduses significantly.