In recent years, many hydraulic, sediment, and environmental researchers focused their studies on river junction hydrodynamics. River junction is an important morphological element of river systems. The incoming FLOW from a minor branch causes extensive variation of FLOW velocity, FLOW discharge, and sediment discharge which results in FLOW turbulence in the main channel. The main characteristic of river confluence is the dimensions of FLOW SEPARATION zone. This zone is developed from the downstream edge where the minor branch enters and extends to some distance downstream into the main channel. There are few parameters affecting the SEPARATION zone extension including the discharge ratio (Qr) the width ratio (Br) and the downstream Froude number (Frd). The effect of these parameters has been investigated on the SEPARATION zone length (L) and width (H). Experimental tests have been conducted in a 90 degree junction. The results show that as Qr increase L and H increases and as Frd increases the value of L and H decreases. In this study relations were developed which can be used for prediction of SEPARATION zone dimensions. The mean value of SEPARATION zone shape index also has been determined.

In the present paper, an experimental and numerical investigation of fluid FLOW and heat transfer in the case of wall injection besides main FLOW through a circular sudden enlargement are studied. The injected FLOW is achieved through an annular slot placed around the inner side wall of the step. The static pressure variation along the sudden enlargement length is measured and calculated at different values of injection ratio (Q) and injection FLOW angles. The average heat transfer with Reynolds number (ReJ) of injected FLOW at different values of the inlet FLOW angle is obtained. The velocity, turbulent kinetic energy and temperature contours are presented in this study. Reynolds number of injected FLOW is varied between 320 and 840, Reynolds number of main FLOW is between 5895 and 8450 and the injection FLOW angles are 0o, 15o, 30o, 45o and 60o. In the injection case, the results indicate that, the pressure recovery coefficient increases by decreasing the injection ratio and increasing the FLOW angle. The average heat transfer coefficient increases as both injection Reynolds number and the injection FLOW angle increase. The numerical results showed that two recirculation zones generate behind the step between the injection FLOW and the main FLOW. The size of these recirculation zones decreases by increasing the injection FLOW rate. The turbulent kinetic energy increases within region between the recirculation zones and main zone also, it decays by injecting FLOW in the recirculation zone. The length for higher value of FLOW temperature decreases by injecting FLOW in the recirculation zone, and that length increases as the injection FLOW rate increases. The comparison between the experimental results and the numerical results gives good agreement using the k-e model with Leschziner and Rodi correction.

In hydrology studies, the river regimes are considered to be natural while this assumption is not correct since the river water is used for developing agriculture, industry, and other needs, particularly in the middle basins. The requirement for river base FLOW SEPARATION is to have access to natural river regime on a daily basis, which, regarding the limitations of naturalization, natural river regime can be calculated on an annual or monthly basis. Therefore, the estimation of base FLOW has been faced with some difficulties. On the other side, due to the complex relation of surface water with groundwater, the estimation of base FLOW is too hard. Therefore, in this study, the removal process method was used for naturalizing monthly discharge of Belbar basin, and Eckhart RDF algorithm was used since it takes aquifer characteristics into account for calculating base FLOW and it has the ability to optimize its parameters. The constant parameters of return and the maximum base FLOW index for monthly natural river discharge in hydrometric stations of Belbar dam were optimized. Then, the monthly base FLOW was calculated and the results showed that the monthly natural river discharge can be used like the daily natural river discharge with the same accuracy.

The Water Column SEPARATION phenomenon is one of the transient FLOW regimes, which is created under conditions such as the sudden closing of the valve or the shutdown of the pump in the water supply network. Hard pressure fluctuations and damages caused by the mentioned phenomenon require identifying and providing a solution to prevent it. By this purpose, the present article investigates the possibility of Water Column SEPARATION in a Loop Water Supply Network using Computational Fluid Dynamics method. Next, the Effect of the inlet velocity on the pressures created due to the Water Column SEPARATION was investigated. For software validation, the Loop system provided by Wang et al. (2017) was selected. After ensuring the efficiency of the software to model the phenomenon of Water Column SEPARATION, simulation was performed at different speeds. Checking the simulation results indicated the occurrence of Water Column SEPARATION in the Intended Network. Also, the Results indicated that with the increase of the input Velocity, the maximum value of the Pressure in the Network increases and its minimum value decreases. In such a way that with a 12% increase in the input velocity, the maximum pressure value changes by 11.8% and the minimum value by 14.26%. In general, it can be said that by controlling the Velocity as an effective factor on the pressure fluctuations of the Water Column SEPARATION, this phenomenon and the resulting damages are prevented.

In this study, a novel fluidic jet actuator is designed to control FLOW SEPARATION on a NACA0015 airfoil at various angles of attack. The U-shaped jet actuator has two rectangular slots implemented near the leading edge of the airfoil. It is driven by a piston mechanism and operates at three excitation frequencies. Depending on the motion of the mechanism, a synchronized jet FLOW is generated by blowing and suction at the dual exits of the actuator slots. The experimental studies are carried out in a subsonic wind tunnel. The unsteady 2D Computational Fluid Dynamics simulations are performed by Detached Eddy Simulation with the SST k-ω turbulence model where measured jet velocities at the exits of the actuator slots are imposed as boundary conditions to mimic motion of the piston. The results at the on-mode and off-mode of the actuator are evaluated in terms of surface pressure coefficient distributions on the airfoil and averaged aerodynamic force coefficients. At low angles of attack, there is an adequate match between numerical and experimental results for the base FLOW without any control. At higher angles of attack, FLOW SEPARATION becomes considerably dominant and stall prevention by active FLOW control is detected especially at high excitation frequencies‎.

Assessing existing water resources along with different routes of the river in a watershed is essential for its optimum use, conservation, and predicting flood and minimum FLOW. In addition, identification of runoff production processes is also important for assessing the effects of climate change and landuse on the hydrologic response of the watershed. There are several methods for separating base FLOW. In this study, the minimum local methods, sliding intervals, fixed intervals, one-parameter recursive digital filter and two-parameters recursive digital filter method were used for separating base FLOW at four hydrometric stations of Karaj River basin with a statistical period of 22 years (1991-2012). Then, the results were compared to determine the most appropriate method. The results showed that at Sierra-Kalvan and Nashtarod stations, the one-parameter recurrsive filter method with alpha of 0. 925 and 0. 950 could be a suitable method for estimating the base FLOW, due to the lack of significant differences between their results, as well as the minimum standard deviation. For Mored and Sierra stations, the one-parameter recursive digital filter with alpha values of 0. 950 and 0. 975 was considered as a suitable method in separating base FLOW because of the lack of significant differences between their results as well as the standard deviation. The one-parameter recursive digital filter, therefore, has high spped in separating the FLOW hydrograph and can determine the continuous values of base FLOW.

Hydrograph analysis is a complex problem in a variety of water resources investigations and its estimate is critical in the assessment of low FLOW characteristics of river for use in water supply, water management and pollution assessment. The paper describes different methods of base FLOW SEPARATION based recession analysis from daily river FLOW records and distinguishes the most suitable method in some hydrometric stations of Azarbaijan province. An automated base FLOW SEPARATION with different parameters –with different parameters of 0.9 to 0.975- and local minimum techniques has been tested against correlation method of master recession curve with base FLOW index. unnecessary of calibration in this algorithms is made easy to use them and Finally, use of digital filter with the parameter set to 0.925 was found to be a most accurate method of base FLOW SEPARATION in study region. Also, Recession constants have fluctuations between 0.65 to 0.83 which reveal role of ground water and base FLOW in river recharging. Continuous investigations of daily FLOW data in long term duration is another benefit of this algorithm that can be used for leaching control and pollutions entry into soil in environmental plannings.

Estimation of Base FLOW Index (BFI), has always been one of the most important issues in hydrology. Base FLOW SEPARATION process, often is done using daily stream FLOW data. Lack of full coverage of daily data for the whole country, may lead to some errors for estimating the base FLOW and its index. In this research, base FLOW index in some catchments of Karkhe basin based on daily and monthly stream FLOW data and using six algorithms were extracted. Three based on recursive digital filter (One-parameter, two parameter and Lynie & Hollick algorithms), and the others on simple smoothing including, Local minimum, Fixed interval and sliding interval methods. Results were analyzed using different statistical methods such as standard deviation, mean absolute error, relative error and other descriptive methods. The results showed that minimum relative error of monthly data compared to daily data was related to two parameter algorithm with 2. 45% and the maximum was related to Lynie & Hollick algorithm with 84. 19 percent. In overall conclusion, two parameter algorithms because of low relative error, minimum Mean Absolute and Root Mean Square Error was recognized as a suitable method for the extraction of base FLOW using monthly data in the absence of appropriate data daily.