فهرست مقالات Unsteady Flow

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  1 - Experimental study of the characteristics of the wake and drag coefficient changes of a car model in unsteady flow
  V. Barzanooni A.B. Khoshnevis
  In this study, changes in velocity, turbulence intensity and drag coefficient in the wake of a notch-back car modelling steady and unsteady flow is measured and evaluated. The blow open circuit wind tunnel is used to simulate fluid flow. Turbulence intensity and nominal چکیده کامل

  In this study, changes in velocity, turbulence intensity and drag coefficient in the wake of a notch-back car modelling steady and unsteady flow is measured and evaluated. The blow open circuit wind tunnel is used to simulate fluid flow. Turbulence intensity and nominal maximum speed of the device is measured to be 0.01% and 30m/s, respectively. The speed has been continuously increased by an invertercausing changes in rotational speed of the electromotor. In the near location to the model, the results showed three different regimes in the velocity profile of the model’s wake. With increasing distance from the model and with increasing the speed, three regimes in the wake are close to each other. Drag coefficient for several velocities is measured, where the result shows that decreasing in drag coefficient is proportional with increasing velocity. In addition, the changing trends of higher order velocity of parameters like flatness and skewedness are depicted. پرونده مقاله
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  2 - Evaluation of Error Due to Applying Average Rating Curve as downstream Boundary Condition in Unsteady Flow Modeling
  مهدی حبیب زاده حسین محمد ولی سامانی حیدرعلی کشکولی
  The rating curve is the relationship between the water stage and the associated discharge in a givensection of a channel. In steady flow, this relationship usually has exponential type, whereas inunsteady it flow has a looped shape. Since direct developing of actual loo چکیده کامل

  The rating curve is the relationship between the water stage and the associated discharge in a givensection of a channel. In steady flow, this relationship usually has exponential type, whereas inunsteady it flow has a looped shape. Since direct developing of actual looped rating curve by usinghydrometric methods is merely possible, steady-state rating curve is commonly used as a downstreamboundary condition in mathematical modeling of unsteady flow which leads to relevant error in modelresults. In this study, in order to evaluate this error, a method is presented by using the HEC-RASmodel of unsteady flow in a prismatic channel with different bed slopes, roughness coefficients andchannel lengths as effective parameters. In various channel geometries , the rating curves of both theapproximate and the reference states are obtained. Then statistical comparison between the results wasdone. Accordingly, 120 R-squared (R2) values refer to 240 different channel conditions, wereconsidered and the errors were analyzed which indicate that the error is declined by increasing bedslope and channel length, in addition by roughness reduction. The maximum rate of the error occurredby any of effective parameters including bed slope, roughness coefficient and channel length wasevaluated in order of appearance; 0.2617, 0.1507 and 0.1673. In addition, the sensitivity of all theparameters in different modeling conditions may be distinguished by using the obtained graphs. پرونده مقاله
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  3 - Sediment Transport in Unsteady Flow Conditions
  Seyed Amin Salamatian Amir Reza Zarrati Mojtaba Karimaee
  Sediment transport under unsteady flow condition is studied experimentally. In the first step, sediment transport under different steady flow conditions was measured and an empirical equation was derived for its calculation. In the next step, two continuous and three st چکیده کامل

  Sediment transport under unsteady flow condition is studied experimentally. In the first step, sediment transport under different steady flow conditions was measured and an empirical equation was derived for its calculation. In the next step, two continuous and three stepwise hydrographs were generated in the flume, and their sediment transport rate was measured. The continuous hydrographs were then approximated by different number of steps. Sediment transport for the hydrographs was then calculated by assuming a steady state condition in each step employing the empirical equation derived in the first step of the study. Results showed that in continuous as well as the stepped hydrographs the difference between the calculated and measured sediment rates is less than 10%. This shows that in the range of the tested hydrographs which conforms to many rivers in Iran, approximating the hydrograph with steady state steps for sediment transport calculations leads to acceptable results. In the next step, the flow and sediment transport in the flume under the tested hydrographs were simulated by using HEC-RAS software. Various sediment transport equations were used and calculated results were then compared with experimental measurements. Results showed that by increasing the number of steps in stepped hydrograph in HEC-RAS, calculated sediment transport rates by each equation tend to constant values. پرونده مقاله