Andrei Dragomirescu

A procedure to develop elevation-area-capacity curves of reservoirs from depth sounding surveys

This paper proposes a procedure for developing reservoir elevation-area-storage capacity curves and bathymetric charts of a reservoir from depth sounding surveys. The Morii Reservoir, located in Bucharest (Romania), on Dambovita River, was chosen as case study. A single beam bathymeter with GPS was used in 2016 to survey the reservoirs bed. The acquired bathymetric data were denoised with a custom-made program written in Python, that uses the Butterworth filter and a zero-phase noise cancellation function. The decontaminated data were subsequently interpolated in ArcGIS to produce a gridded DEM of the reservoir bed surface and a bathymetric chart with contour lines. The area-capacity-elevation curves were obtained by calculating the 2D area and volume between horizontal planes and the interpolated bed surface. Comparisons with bathymetric survey from 2010 show differences of less than 14% in terms of storage capacity and 8% of the area of the reservoir during these 6 years.

Numerical investigation of the flow in a modified Bánki turbine with nozzle foreseen with guide vanes

This paper presents results of a study aimed at verifying whether the usage of a cascade of guide vanes inside the nozzle of a Bánki turbine could improve the turbine performance. Bánki turbines are small cross-flow water turbines used to harvest renewable energy, usually in a range from a few kilowatts to a few hundred kilowatts. First, an existing turbine with classical nozzle was experimentally and numerically investigated to provide a basis for comparison. A mesh sensitivity analysis was performed to find the most appropriate mesh parameters in terms of accuracy and computational resources. After choosing the mesh, the numerical results were validated against experimental data. Second, the turbine with the nozzle modified to accommodate a cascade of guide vanes was numerically investigated. Comparisons of the results obtained on the two nozzle geometries show that the turbine with nozzle foreseen with guide vanes performs clearly better than the classical turbine. The guide vanes assure absolute velocity angles that are closer to the design value. The moment delivered by the modified turbine is significantly higher than that of the classical turbine. Hence, the usage of a nozzle with guide vanes is expected to provide a higher turbine efficiency.

On the Variation of the Polytropic Exponent in a High Pressure Fan Impeller

Fan impellers are usually designed considering that the pumped air is incompressible and homogeneous, i.e. its density remains constant. When the incompressibility hypothesis can lead to significant errors, as in the case of high pressure fans, the analysis of the air flow can be made by considering that the air undergoes a polytropic process of constant polytropic exponent. In this paper, the concept of polytropic process of variable exponent depending on impeller radius is introduced, in order to better approximate the phenomena that take place inside blade passages. Numerical results obtained for an impeller of a high pressure fan without spiral casing suggest that the pumped air undergoes two different processes: an expansion in the first part of the impeller and the usual compression in the second part. The two processes are reflected in the strong variation of the polytropic exponent, which shows a vertical asymptote where the change of the process takes place. The results also suggest that high pressure fan impellers could consist of two stages, each stage being designed according to the process that takes place inside it: expansion or compression.

Experimental Investigations and Numerical Simulations of the Viscous Flow around T-Profiles

This paper investigates both experimentally and numerically the flow of a viscous fluid around T-profiles, i.e. T-shaped bodies, having different geometries. Of main interest it was the vortex shedding behind the T-profiles with an eye towards its application to flow measurement in open channels. Another purpose of the study was to assess to what extent different numerical models can be used to accurately predict the flow in the vortex street behind T-profiles.