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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 identity 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 ±10 flow angles.

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Lullaby is a kind of motherly song which is used to put infants into sleep, but one type of formal literature in the constitutional period inspired by these lullabies targeted the awareness and awakening of common people. The current research explores Mirza Ali Akbar Saber (1279-1329), Abulghasem Lahuti (1264-1336), and Sayed Ashrafaldin Gilani’s (1352-1287) lullabies. The goal of this study is to introduce these types of lullabies, the reasons of their songs, the analysis of their structures and contents, and the differences of such types of lullabies with the conventional ones. The methodology of this research is descriptive-analytical. The data was gathered by library and document analysis. The results indicated that the lullabies were formed under social, political, and psychological circumstances of that period. The secret of success of this type of poem in communicating with its addressees in transacting political issues and making the people aware lies in its simple language, traditional literature, the naturalness of literary methods, and the avoidance of intricacy. Finally, the results illustrated two different discourses by the poets of these poems which are investigated in this study.
 

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This article investigates experimental study of the flow field on a blunt airfoil. For this purpose, PIV technique based on instantaneous flow structures is used in order to view and two dimensional investigation of flow field around unmodified and blunt airfoil and at different times. This study is performed on flows at very low Reynolds number(Reynolds number lower than 4500). This flow regime is very similar to dominant condition on micro air vehicles (MAVs). In order to validate the method used in this study, flow field around cylinder is considered and in continue, instantaneous and mean velocities fields, streamlines and mean vortices field around unmodified and blunt airfoils are obtained. The results show that there are prominent differences on the structure of wake around airfoils and sizes of separation region for blunt and simple airfoils. Meanwhile separation of the flow for both blunt and simple airfoils at this very low Reynolds number, is occurred at angle of attack 5 (at low angle of attack). Also generation of vortex at wake region and their position and circulation at different times, are discussed.

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In present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. These experiments were conducted in four different locations X/L= 0.85, 1, 1.25 and 1.5 downstream of the model at Reynolds number of 3.85×105 by a five hole probe. The effect of various factors such as the variation of Reynolds number, the installation of the trip strip on the model nose surface, the mounting of the appendages on the submarine bare hull model and the nose shape effect on the wake structure were investigated in this study. The results showed that the installation of the trip strip on the nose surface did not have recognizable effects. By Increasing the Reynolds number, the amount of the dropping velocity in the wake field decreased due to the decreasing of the separation region on the after-body section. Presentation of the appendages on the model surface lead to the increasing of the wake area. The effect of the nose shape on the wake of the submarine model is the main innovation in the present work. Investigations showed that the velocity in the central part of the wake for non-axisymmetric nose shape (TANGO) decreased in comparison with the axisymmetric nose shape (SUBOFF and STANDARD).

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In open channels, the distribution of velocity, shear stress and other related quantities such as the diffusion and dispersion coefficients and thus all transport processes are three-dimensional, according to the three-dimensional convection and diffusion principles. Determining the velocity distribution- as a key parameter for estimating other hydraulic parameters- has always been the subject of attention. Velocity distribution in the inner region of the flow (y0.2D). The log-Wake law is of the most accepted laws for velocity distribution in wide open channels, this law modifies the logarithmic law by adding a Wake function; but in case of narrow open channels, the log-Wake law deviates from the measured data near the free surface. Because the profile by the log-Wake law depicts the velocity which increases with the increase of distance from the bed monotonically and is not able to show the velocity negative gradient near the free surface which happens in narrow open channels. In narrow open channels, the three dimensional structure of the flow and the transport momentum from the side walls to the central zone due to strong secondary currents, causes the maximum velocity to occur below the water surface which is called velocity-dip phenomenon. The velocity dip phenomenon was first reported more than a century ago. Since that time, numerous investigations have been conducted by many researchers in order to propose new models to be able to not only describe the dip phenomenon and negative gradient of velocity near the free surface, but also to predict the position of the maximum velocity accurately and fit the experimental data throughout the whole flow depth.
This paper introduces an analytical model based on Reynolds Averaged Navier Stokes (RANS) equations and an eddy viscosity distribution, to estimate velocity distribution in turbulent fully developed flows. The proposed model is suitable for both narrow and wide open channels, and is capable of predicting the dip phenomenon. The results by the model verified with data measured in several rectangular lab channels and data collected from an actual sewer channel. Since the proposed equation for velocity distribution is dependent of Coles Wake parameter (Π), the effect of this parameter on level of accuracy and description of velocity profile as well as prediction of dip phenomenon and location of maximum velocity has been studied. Many researchers proposed different values for Coles parameter, and it seems there is no universal constant value for this parameter. In this study, the value of Coles parameter was proposed by fitting the data from different channels, based on the least error calculated in predicting the velocity profiles by the proposed model. The results show that the profiles by the model agree well with experimental data and predict the velocity-dip phenomenon; also the model provides little errors compared to measured data in the channels, which is representative of high level of accuracy in defining velocity distribution profile of the flow. The value of Coles parameter estimated for channel-sewer was less than that for lab channels.

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present study is done to evaluate the effect of parameters like trip strip installation, free stream velocity, geometery of model nose (SUBBOF nose and DRDC nose) and putting up model in pitch and yaw angle, on drag coefficient. also the effect of stand geometry of an axially symmetric model in wind tunnel on wake flow structure and drag coefficient in zero and ten degree angles of attack was investigated. choosing best distance behind the model for data acquisition in order to calculate drag coefficient under consideration of turbulence effects in one dimension is the other item to investigate in present study. all experiments have been done in an open circuit wind tunnel at university of Yazd and data acquisitions has been done with a one dimensional hot wire. according to calculations installation of trip strip enhanced drag coefficient in all cases. also drag coefficient decreased with increasing free stream velocity. putting up the model in pitch and yaw angle of attack increased drag coefficient. between two nose shapes that examined, the SUBBOF nose shape choosed as suitable nose. a stand with NACA0012-64 geometry and Rod stand were selected as the most appropriate stands for zero and 10 degree angles of attack.

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Wind turbines are highly complex structures for numerical flow simulation. Today, developments and increasing the use of wind energy in the world has created a demand for increasingly accurate and efficient models for wind applications. Wind turbine wakes have significant effects on decreasing the produced power and blades fatigue loads. thus, the wakes study has great importance in wind turbine simulations. Actuator line model (ALM) is one of the most accurate models for characterization of the flow field and the turbulent wakes created by the turbines. AL model does not require boundary layer resolution and is thus significantly more efficient than the fully-resolved computations. this model can accurately simulate the wakes of wind turbines operating in a flow field without any need to create or import the CAD models of turbine and just by using turbine parameters. In this paper, AL method implemented in openFOAM solver and a new method used to spread forces on actuator lines. in order to validate the results, MEXICO rotor was modeled and large eddy simulation’s turbulence model is used to investigate the flow field around wind turbine. Simulation has been done for two different conditions include design conditions and stalled conditions. Results obtained for predicted wakes and performance parameters, were compared to experimental data and it was observed that the ALM results agree well with measured data. Stall condition’s results were in better agreement with experimental dada so that the thrust had 8.5% difference and the toque and power had 2.8 and 2.4% respectively.

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In this article, the effects of helicopter main rotor blade tip geometric shapes on the aerodynamic of hover flight are analyzed. Aerodynamic coefficients, vortical flows and vortex wakes are discussed. Fluent software with implicit finite volume method has been used for numerical simulation process. The grids are structured. Experimental results of the Caradonna and Tung have been used for aerodynamic validations. In this investigation, the flow has been considered turbulent, compressible, and viscous. The results of several RANS models for a specific rotor have been compared together and finally the standard k-ε turbulent model has been selected. The Roe method with second order scheme was selected. Thirteen different geometrical shapes on the tip of the blades have been presented and the results of the models have been compared together. These studies show that the blades of BERP IV, Blue edge, Actual, Bell-214 and BERP III produce maximum thrust and MIL-17, Sikorsky RH-53D, Tapered, Bell-412, Sikorsky SH-3D and Comanche RAH-66 produce minimum torque and also the blades of BERP III and IV, Ogee and Bell-214 produce maximum torque.

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Guidance of an underwater vehicle in the wake of target due to the complexity of guidance in water and also sensor limitations, is still the most important homing guidance method. Disadvantages of wake guidance can be mentioned as zigzag motion for rediscovering the wake in its path which according to the decreasing linear speed of approaching the target, sometime it doesn't reach the target and collision fails. Therefore various ideas, with both positive and negative aspects, have been introduced to improve movement in the wake path. According to complexity of the wake model and also its instability in order to extract its parameters, makes it a very nonlinear phenomenon and guidance in it is a problematic in underwater vehicle. Since the wake detection area by the sensor is not enough widespread, wake is just discovered in the near of itself. Hence the real wake path is not detectable and therefore advanced guidance method is not available. For this reason, it is suggested to use a method of unknown path tracking for the wake guidance. This guidance law consists of two parts of path estimation and nonlinear guidance. The estimation method is performed using particle filter that has the ability to estimate nonlinear paths. The stability proof of nonlinear guidance method is done by Lyapunov.

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Research on atmospheric boundary layers in wind farms is an important task. Especially, wind effect on wind turbines installed in mountainous area with complex terrain is complicated. In this research, the wake of a wind turbine and wind flow in complex terrain have studied with computational fluid dynamic (CFD) method in OpenFOAM software. Actuator-disk model with introducing forces, based on Blade Element Momentum Theory, on the disk are used. For simulation of wind turbine in wind farm, Reynolds averaged Navier Stokes equation with k-ɛ turbulence model has been used. Structured mesh was used for simulation domain. Also, main wind direction has been determined from North toward south considering wind rose of area. One of wind turbines is studied by detail. The numerical results show an extended wake effect around 5d (five times the rotor diameter). Wind speed deficit is 26% at this distance. Captured wind power from the simulation is close to real data. Also, wind regime has been studied and analyzed for different seasons. For November, December and January, the time period that wind blows in effective speed, is decreased less than %50 which is important in wind farm design and operation.

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The flow field investigation around marine propellers is of great importance, due to its applications in vessels identification and hydrodynamic noise prediction. In the present research, the steady and unsteady wake flow field was simulated using the open-source OpenFOAM software and the simple-Foam and Pimple-DyMFoam solvers. The obtained characteristic chart and near propeller wake flow results were validated against available experimental data, which shown to be in a very good agreement. The grid study results in the wake region prove that unlike global quantities, the employed wake grid strongly affects the wake parameters. The results obtained from the present research show that employing the RANS models are suitable for the hydrodynamic coefficients calculation and these models predict the results with a low computational cost against the Unsteady RANS approach. On the other hand, an accurate investigation of the flow fluctuations and the vortex flow instabilities can only be accrued performing unsteady simulations with an appropriate refined grid. In this research, the effect of advance coefficient is also investigated on the vortex flow pattern in the wake region. Qualitative comparison of the obtained results and similar available data of the more accurate DES turbulence model shows that the URANS method has great capabilities in wake flow simulation provided that a suitable grid is applied. This method significantly decreases the required cells number and run time while maintaining the results accuracy.

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In the present research, numerical simulation of the characteristic chart and steady-state Wakefield flow around a marine propeller is conducted. Solutions were performed using the open-source OpenFOAM software and the steady incompressible simple-Foam solver. The gradients were calculated using the linear Gauss algorithm, and the pressure equation was solved with the multi-grid method. In this research, characteristic chart simulation of the propeller was carried out for the entire operational conditions and the effect of using Realizable-k-ε and k-ε-v^2-f turbulence models on the results was investigated. The results were found to be in good agreement in all conditions except for the near bollard region. In this region, the propeller inlet angle of attack severely increased, and the two equation model predicted the thrust coefficient with 24% error, while implementing the four equation model significantly developed the results and decreased the error to 5%. The wake region parameters were also investigated in the numerical simulations at different longitudinal and radial cross sections behind the propeller which showed good agreement compared with the available experimental data. Wake region investigation showed that the flow behavior in downstream cross sections is similar to the corresponding upstream section with smaller variation ranges and for the swirling flow behind the propeller, the maximum and minimum angular position of the wake components rotates. The obtained results also show that the wake axial velocity component deviation is extremely large at the blade tip.

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In this paper, the axisymmetric actuator disk method (2D) with acceptable accuracy and low computational cost based on computational fluid dynamics have been adopted to study the flow behavior around the horizontal wind turbine rotor and the wake. For this sake, a C code is developed as a self-developed user-defined function (UDF) in commercial software package ANSYS FLUENT. The rotor is modeled as a virtual disc and its effect is added to the Navier-Stokes equations as a sink term. The results obtained for the 5 MW NREL wind turbine in this study show the appropriate accuracy and speed-up. The interaction of two wind turbines in the wind farm has been investigated. The results depict that the output power and thrust of the downstream rotor due to the presence of an upstream turbine drop up to 88% and 57%, respectively. Also, radial distribution of the downstream rotor power shows that at a closer distance, the middle part of the blade has a larger contribution to power generation. Further, the effect of downstream rotor on the upstream rotor performance is up to 1.5% and 0.7% reduction in power and thrust respectively.

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In the present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. The experiments were conducted to determine the effect of the location of control surfaces on the wake inflow to the impeller of the submarine. In order to investigate the effect of the location of control surfaces as the most important innovation of the present study, the aforementioned surfaces were installed in three longitudinal positions X/L=0.89, 0.92, 0.95 on the heel of the submarine model, and the wake flow was measured at position X/L=1.7 and the Reynolds number 6*10^5  by a five-hole probe and a hotwire anemometer. Finally, the longitudinal position X/L=0.95 was selected as the optimal location for the stern planes to improve the wake inflow to the impeller in terms of reducing its total area and the least amount of turbulence and non-uniformity. The results obtained during this study showed that arriving of the holder basechr('39')s wake to the stern area increases ​​the area and average velocity and subsequently reducing the non-uniformity of the wake flow.

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New generation of wind turbines, in comparison to the old versions, have been designed with colossal blades to produce larger amount of power output. However, this has led into some unpredictable challenges including their construction procedure and expenses and particularly blades’ transportation. To overcome these issues, multi-rotor wind turbines have been suggested. Aerodynamic performances of such turbines have been previously assessed by other investigators. However, the wake characteristics of these turbines have been less studied. The focus of the present research is on the assessment of these characteristics, which are crucial in the process of any wind farm design. For this purpose, wake flow of a small three-rotor wind turbine is numerically simulated using computational fluid dynamics. A numerical simulation has been conducted for a single-rotor wind turbine and three-rotor small horizontal axis wind turbine with the angle of 180^⸰ arrangement. The results of single rotor wind turbine indicated that far downstream wake extended up to 8D, with Jensen-Gaussian model can be better predicted. The comparison between three bladed wind turbine and the results of wake models for the equivalent turbine showed that because of wake interactions in the downstream of the rotor, the loss of turbulent kinetic energy and recovery of the stream speed will be faster. As a result, in the wind farms, the turbines in closer distances around 4D of the equivalent signle-rotor wind turbine can be installed.