Institute for Hydraulic Research

Ljubljana, Slovenia

Institute for Hydraulic Research

Ljubljana, Slovenia
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Novak G.,Institute for Hydraulic Research | Rak G.,University of Ljubljana | Preseren T.,Institute for Hydraulic Research | Bajcar T.,University of Ljubljana
Flow Measurement and Instrumentation | Year: 2017

Waste-water channels or physical hydraulic models often convey shallow water flows with depths around 5 cm. Such free surface flows can in principle be measured using standard measuring flumes or thin-plate weirs, but proper employment of these is often practically impossible, e.g. due to limited space. To avoid this, various flow meters with contact probes (i.e. »area-velocity« probes) are employed instead, but in reality this often results in inaccurate measured values of discharge. This paper presents an effective way to determine discharge of very shallow flow without intruding the flow. Our approach is based on computer aided visualization, namely on the quantification of the field of vectors representing local velocities on the water surface of the flow. In contrast to other studies, this method does not require complex measuring equipment, special lights or special devices for the seeding of particles. Experiments were conducted in 0.5 m and 1.06 m wide rectangular channels, made of glass and concrete, respectively, and they show that this method could be employed both in hydraulic laboratories and in the field. Measurements showed that velocity on the surface of the shallow water flow differs from theoretical average mean flow velocity in the observed cross section, and further that this difference increases with the decrease of water depth. This suggests that the assumption, which states that in shallow water flows the surface velocity is similar enough to the mean flow velocity, is not necessarily correct. © 2017 Elsevier Ltd

Bombac M.,Institute for Hydraulic Research | Cetina M.,University of Ljubljana | Novak G.,Institute for Hydraulic Research
Ecological Engineering | Year: 2017

Design of effective fishways is becoming increasingly important. This paper focuses on the effect of the angle of deflection (α) between small and large baffles in a vertical slot fishway (VSF). A reliable depth-averaged two-dimensional numerical model PCFLOW2D was used to perform simulations of various VSF configurations, including six angles of deflection, two slot sizes, two large baffle sizes and four water level differences between adjacent pools. The results showed the important influence of α on depth-discharge curves and maximum velocities at the slot which both strongly affect the fishway efficiency. With larger α, up to 42% smaller discharges and up to 33% smaller maximum velocities were calculated. In cases with small α and larger slot sizes much greater maximum velocities than theoretically calculated using over simplified formula were modeled (up to 62%). The important effect of transverse displacement of the slot on discharge and maximum velocity was evaluated. As expected, the most important parameter that determines the discharge and maximum velocity in the fishway is water level difference between adjacent pools. With slot layout optimization it is possible to achieve the same discharge and maximum velocity even at larger water level differences between adjacent pools which obviously reduce fishway construction costs. © 2017 Elsevier B.V.

Bombac M.,Institute for Hydraulic Research | Novak G.,Institute for Hydraulic Research | Mlacnik J.,Institute for Hydraulic Research | Cetina M.,University of Ljubljana
Ecological Engineering | Year: 2015

Fishways are of great ecological importance and have been the focus of numerous studies. However, many fishways remain operating at an unsatisfactory level. Furthermore, field measurements of flow properties in effective fishways remain surprisingly rare compared to the number of various numerical and physical hydraulic models. The purpose of the research was to conduct extensive field measurements of the flow in an effectively operating vertical slot fishway (VSF), and to use the findings to calibrate and verify the depth-averaged two-dimensional (2D) numerical hydraulic model PCFLOW2D. Flow velocities were measured using a reliable 3D acoustic probe. Measured velocities were up to 50% larger than values calculated from an equation proposed in recent literature, but in accordance with results of our simulations. PCFLOW2D proved to be a useful tool for modeling fishway flow and could be used in similar hydro-environmental problems. © 2015 Elsevier B.V.

Bombac M.,Institute for Hydraulic Research | Novak G.,Institute for Hydraulic Research | Rodic P.,Institute for Hydraulic Research | Cetina M.,University of Ljubljana
Journal of Hydrology and Hydromechanics | Year: 2014

This paper presents the results of an experimental and numerical study of a vertical slot fishway (VSF). A 2-D depth-averaged shallow water numerical model PCFLOW2D coupled with three different turbulent models (constant eddy viscosity, Smagorinsky and k-ε) was used. A detailed analysis of numerical parameters needed for a correct simulation of the phenomenon was carried out. Besides the velocity field, attention was paid to important hydraulic parameters such as maximum velocity in the slot region and energy dissipation rate ε in order to evaluate the performance of VSF. A scaled physical hydraulic model was built to ensure reliable experimental data for the validation of the numerical model. Simulations of variant configurations of VSF showed that even small changes in geometry can produce more fishfriendly flow characteristics in pools. The present study indicates that the PCFLOW2D program is an appropriate tool to meet the main demands of the VSF design.

Muller M.,DHD Ltd | Novak G.,Institute for Hydraulic Research | Steinman F.,University of Ljubljana | Rak G.,University of Ljubljana | Bajcar T.,University of Ljubljana
Strojniski Vestnik/Journal of Mechanical Engineering | Year: 2015

Bottom-hinged flap gates on side weirs are often used for the regulation of flow diversion in case of water abstraction for a variety of needs. In this study, a new equation for the discharge coefficient of a bottom-hinged flap gate on a side weir was proposed on the basis of discharge measurements. The equation was divided into two parts. The first part covers the impact of the sharp-crested side weir and the second the influence of the position and the width of the flap gate. In this manner, the discharge coefficient can be calculated with other authors' equations for a sharp-crested side weir, which then must be multiplied by the new proposed coefficient. Very good agreement was found between the obtained discharge coefficients and the one calculated with the proposed equation. Furthermore, the results were compared with the equations of other authors for the discharge coefficients of sharp- And broad crested side weirs. The agreement was found to be very good. Additionally, measurements of water levels along the edge of the flap gate and measurements of the velocity field were carried out with a computer-aided visualization method. From these measurements, it was possible to show that the contraction of the water jet varies with the gate-opening angle. It was also found that the side weir with a flap gate has the most favorable hydrodynamic shape around the gate-opening angle of 33°, where the discharge coefficient reaches its maximum. © 2015 Journal of Mechanical Engineering. All rights reserved.

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