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The performance of turbine section of a gas turbine deteriorates over operation because of working in high temperature conditions and characteristics of the entry gas. On the other hand, due to complexity of the flow field within the turbine, three-dimensional analysis is required. This paper presents a numerical study of roughness effects on turbine flow field and performance. In this paper, effects of blade surface roughness caused by operation conditions on turbine performance were numerically calculated. Numerical calculations were carried out for the fourth stage of an axial turbine which was experimentally tested in the technical university of Hannover, using ANSYS software. Calculated results were verified with the measured data and showed a good agreement. To find out the effects of blade surface roughness on turbine stage performance and flow field, Two equivalent sand-grain roughness heights of 106㎛ (transitionally rough regime) and 400㎛ (fully rough regime) in four different mass flow rates were considered. Results showed that summation of efficiency reductions of the rough stator and rough rotor approximately equals to that of the totally rough stage for each roughness height and effect of stator roughness on efficiency reduction is same as the effect of rotor roughness on stage efficiency.

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High temperatures and different properties of entering gas into the turbine of a gas turbine cycle can decrease its performance. Considering the complexity of the flow distribution inside the turbine, three-dimensional analysis to find out the flow and temperature field in the turbine stages is very important. As time passing the increasing of the roughness of blades is unavoidable. The aim of this paper is investigation of the blades roughness effects on flow field and efficiency of gas turbine with numerical calculations. In this research, a two-stage turbine is modeled in the form of three-dimensional and the results are validated with experimental data. Then the effects of blades roughness on flow field and performance of turbine in five pressure ratios is investigated. Also, in order to determine the role of stators and rotors in decreasing the turbine efficiency, in a special roughness, the first and second stators and then corresponding rotors have separately been examined and then this phenomenon affected on blades simultaneously. Results showed that the efficiency drop by applying all together on the turbine stage is approximately equal to summation of efficiency drops by applying separately.

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With respect to special conditions apply to the gas turbine, its blades are affected by many different factors such as, hot corrosion, oxidation, wear, impact of external particles, and etc. and are destroyed. Due to the reduction of their working life time, the turbine efficiency reduces and ultimately the heavy costs of periodic repairs are needed, and also new replacements of their blades are unavoidable. The aim of this study is investigation of the effects of corrosion and blade damage on flow field and gas turbine performance, by numerical simulation. In this research, a two stage turbine is modeled in the form of three dimensional and the results are validated with experimental data. To analyze of the behavior of entire flow, conservation of mass, momentum, and energy equations are solved. The numerical simulation of the turbine is done with ANSYS CFX software. Then the increased rotors tip clearance effects with decreasing thickness due to corrosion in both nozzles and blade leading edge and trailing edge were separately studied on turbine flow field and its performance in five actual different pressure ratios. The results showed that the most important factor in reducing the efficiency of gas turbine is due to rotor tip clearance increasing. Also corrosion of the blade edge respect to the trailing edge damage is a little more affected on reducing efficiency and increasing loss coefficients.

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Submerged vanes are small flow training structures, designed to modify the near bed flow pattern and redistribution of flow and sediment transport whit in channel cross section. The vanes generating secondary circulation in the flow. The flow field around lateral intake located in the outer bank of channel bends and the interaction between this flow field and secondary flow due to submerged vanes in completely three dimensional and complex. The purpose of this paper is determination of appropriate location of the one submerged vane with respect to the downstream and upstream edge of the lateral intake in a U shape channel bend and choice the best angle of vane for reduce the sediment entry to the lateral intake. In this order we use the Fluent software to numerical simulation of 3D flow pattern around the one vane that locating in front of downstream edge of a lateral intake in a U shape channel bend. The results of numerical were verified with the existing experimental data. Comparison of the predicted x velocity and y velocity field with laboratory measurements indicates that the model capture experimental trend with reasonable accuracy. Computations are performed using Reynolds Stress Model. After model verification, the effect of different position of the vane with respect to downstream of intake (the first, middle and end point of vane is in front of downstream edge of intake) and upstream edge of intake (the first, middle and end point of vane is in front of upstream edge) and effect of different angle of vane (15, 17, 20, 25, 30 degree) on flow pattern and shear stress pattern of bed is considered. The appropriate position and angle of the vane has been selected by effect of the vane on area of high shear stress zone and area of low velocity contour around the vane and reduction of dimension of saddle point near the downstream edge of lateral intake and situation of stream line around the vane and in front of the intake at the bottom of the channel. The results show the best position of vane with respect to downstream edge of lateral intake is the case that the first point of vane is in front of downstream edge of intake and the best position of vane with respect to upstream edge of intake is the case that the end point of vane is in front of upstream edge of intake. Also the results show that the appropriate value for angle of attack of the vane at downstream edge of intake (the first point of vane is in front of downstream edge of intake) is about 20-25 degree and optimum value for angle of attack of the vane at upstream edge of intake (the end point of vane is in front of upstream edge of intake ) is about 17-20 degree.

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Due to the complex structure of the pressure-adjusting device used in most sprinklers for variable irrigation, it is not possible to observe the flow behavior of the water passing through the flow field. In this paper, an integral three dimensional (3D) numerical model based on the structural characteristics of the fluidic sprinkler was constructed to simulate the flow field distribution using computational fluid dynamics (CFD). A new type of fluid sprinkler (BPXH) was used in the experiments. The main stream region and the variable velocity regions were clearly distinguished, and the details of the variations in pressure are discussed. The results indicated that the simulation methodology generated sufficient data to analyze the sprinkler pressure and outlet velocity changes. The minimum error of the difference between the simulation and the test pressure values was 0.049, with a maximum of 0.14. The turbulence model could accurately predict the relationship between the outlet velocity and the wetted radius. The outlet velocity ranged from 12.6 to 17.9 m s-1 during the simulation under the variable inlet boundary conditions of the sprinkler. Both the simulation and test values of the wetted radius increased gradually with the sprinkler rotating angle. The absolute error of the simulation and the test ranged from 0.07 to 0.16. Computational fluid dynamics provides a promising tool to help in the design of pressure-adjusting devices using a new type of variable-rate fluidic sprinkler.

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Spur dike is one of the river training structures that is considered to deviate the river from critical and erodible areas and the flow from the sides and towards the central axis. As a result of flow is developing a circular area with high turbulence around the spur dike. The hydraulic process results development of the scour hole on the upstream of the spur dike and settlement of sediment in the downstream and sides of the river. While scouring in spur dike structures results a serious threat to the river so it is needed to be researches in this field. This paper describes triplex repellent shielded spur dikes (directed to the upstream) with a distance of 3.5 times of the effective length of the spur dike in the outer bank of the channel. The first spur dike is located at 30 degree from the start of bend. The experimental channel is a 90º channel with rectangular section. The radius of curvature to the channel width is 2, which is classified as a sharp bend. Materials used are sands with uniform grains and its mean diameter is 1.28mm and its standard deviation coefficient is 1.3 and the relative density of sediment is 2.35. The results of flow field on flat bed and a scouring experiment are presented. Discharge was 25 l/s and All scour tests were done in 24 hours and in the moving threshold conditions (U/Uc =0.98) and clear water condition. Flow field is recorded using the Vectrino II velocimeter that can profile water in a 3cm column. It was found that in the levels upstream of the first spur dike in an adjacent to bed, stream lines are deviated to the inner bank. While in the middle levels, flow lines upstream of the spur dike is almost parallel to the channel walls and approached the spur dike, resulting deviation in the separation zone. In the scouring experiment it was obvious that at the beginning of the experiment, thus creating the down flow upstream of the spur dikes scouring initiates near the wing of each spur dike and it develops by the horse shoe vortex. But with the time sediment had been washed from upstream of the first spur dike, and moved to the foot of the spur dike until it reaches upstream of the former to the latter. Then scour hole upstream of the second spur dike starts to form. Results showed that the amount of scour upstream of second spur dike is 33 % and upstream of third spur dike is 81 % the maximum amount of scour that occurs upstream of the first spur dike. Mechanism causing scour and flows occurring within this range detailed in this paper.

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In the present study, the effect of high temperature radiant heaters’ arrangement on providing appropriate and uniform thermal conditions under asymmetric flow field have been investigated in an industrial environment. For this reason, a sample industrial environment with one inlet and outlet opening has been considered with two different types of high temperature radiant heaters’ arrangement: single radiant heater and couple radiant heaters. For the mentioned conditions, continuity equation, momentum equations, energy equation and radiative transfer equations have been solved by OpenFoam numerical solver. Also energy consumption has been evaluated in the present study. The results show that in presence of asymmetric flow field, using couple high temperature radiant heaters in comparison with single radiant heater causes more uniform temperature distribution and decrease about 10 degrees of Celsius in maximum temperature of floor. Also, this can cause to decrease about 35 percent in floor temperature distribution deviation from the average appropriate temperature (27 degrees of Celsius). Moreover, the results indicate that utilizing couple high temperature radiant heaters leads to increase in energy consumption about 10 percent in comparison with single radiant heater.

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One of the most important parts of the polymer fuel cell is the bipolar plate, which through the channel paths as the flow field in these plates, the availability of reactive gases to the surface of the catalyst layer is possible to carry out the electrochemical reactions of the fuel cell. So far, many researchers have been designing different flow streams for fuel cells, although each of the models has its own advantages and disadvantages, but a suitable design for the fuel cell flow field, which has a uniform distribution of reactive gases on the surface of the catalyst layer, Access to higher performance and longer fuel cell life is very important. In this paper, we introduce a new flow pattern for fuel cell flow field, and the numerical results obtained with a conventional parallel model are compared. The flow-shaped designs have been modified with a spiral and the total dimensions of the cell are 6400 mm 2, which has allowed access to uniform distribution of reactive gases, flow density and temperature distribution. An increase of 66% was achieved with a limited density and increased 1.7 times the power density by adjusting the arrangement for the flow field. Therefore, considering the design of the fuel cell based on the power density curve presented in the new model, the specific characteristics and power of the fuel cell in an air mission have been addressed and the availability of high specific power that is of particular importance in aerial applications is achieved.

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