The impeller and volute of a single-channel pump used for wastewater treatment were simultaneously optimized to improve the hydraulic efficiency and reduce unsteady radial force sources due to impeller–volute interaction. Steady and unsteady Reynolds-averaged Navier–Stokes equations were solved with the shear stress transport turbulence model as the turbulence closure model using tetrahedral grids to analyze the internal flow in the single-channel pump. Five design variables related to the internal flow cross-sectional areas of the impeller and volute were selected to simultaneously optimize three objective functions: the hydraulic efficiency, the sweep area of the radial force during one revolution, and the distance of the mass center of the sweep area from the origin. A response surface approximation model and a genetic algorithm were employed to obtain the three-dimensional Pareto-optimal solutions representing the trade-off between the efficiency and the radial force sources. The three-objective optimization results showed that the representative clustered optimum designs exhibit enhanced efficiency and reduced radial force sources simultaneously in most cases, compared with the reference design. The trade-off relationship between the efficiency and the radial force sources clarifies with controlling the internal flow cross-sectional areas of the impeller and volute of the single-channel pump. The efficiency improvement and reduction in the radial force sources were systematically verified by analyzing the detailed internal flow characteristics.
Sediment erosion is the main problem for the hydropower situated in South Asia and South America. Due to sediment erosion, hydropower in those areas cannot operate in their full potential. Sediment erosion is a significant problem in turbomachinery and associated with degradation of turbine performance. The sediment erosion removes the turbine material from its surface. It can cause fracture of the turbine, which leads to an economic loss. In this paper, the sediment properties and its influence on erosion have discussed. Sediment properties like shape, size, and concentration have a direct influence on erosion. The numerical analysis was conducted to visualize the erosion in Francis hydro turbine. The most vulnerable area for the sediment erosion in Francis hydro turbine has predicted. The precise prediction of the sediment erosion in the turbine is the difficult task due to the synergetic effect of sediment parameters (shape, size, concentration, hardness, velocity). The accurate and precise indication of the sediment erosion required both experimental and computational analysis. In this study, solid-fluid computational analysis has done to identify the susceptible area on runner blade and influence of sediment parameters on erosion.
The hydro-abrasive erosion poses challenges for smooth and eﬃcient operation of existing hydropower plants (HPPs) as well as planning for new HPPs. The loss in revenue is caused due to reduced generation on account of reduced efficiency, down time for repair and maintenance for restoring the machinery and other components. In this study, various optimization considerations required with respect to hydro-abrasive erosion at both the planning and the operation stage of a HPP are presented. The factors involved in each steps like unit sizing, selection and design of turbines, capacity of desanders, cut-off limits of sediment concentration for turbine switch-offs, preventive measures such as coatings etc. were discussed. Further, a case study of an operational HPP located in Indian Himalayas is presented where suspended sediments, hydro-abrasive erosion and reduction in efficiency were measured simultaneously. Available models were used with measured values to obtain various losses due to hydro-abrasive erosion. The cost of coating, a preventive measure, is compared with the losses in operating the uncoated turbine. A decision making criterion is also introduced.
In the present study, the suction performance and the cavitation instabilities in turbo-pumps with three different inducers designed with different design incidence angle are experimentally investigated in the wide range of operating flow rate. Three inducers L with the lowest design incidence angle, M with the moderate one and H with the largest one are used in combination with identical main impeller. As a result, the total head of pump with inducer H is confirmed to be the largest especially at large flow rates, while the shaft power is almost the same, resulting in the best efficiency with the inducer H. The suction performance is the best with inducer H at large flow rates and is the best with inducer L at low flow rates. Two kinds of instabilities, the cavitating whirling vortex and the surges are mainly observed for the all both inducers, but they are limited at low flow rates. The occurrence ranges of these instabilities in terms of the operating flow rate is the widest with inducer H. However, those in terms of the shockless flow rate ratio is similar for the all three inducers: This fact can contribute to establish some guideline to the pump operation avoiding serious flow instabilities.
This paper presents a joint experimental and numerical analysis of the erosive potential of an unsteady cavity that develops at the leading edge of a two-dimensional hydrofoil and periodically sheds vapour clouds. From an experimental viewpoint, the erosive potential was characterized by pressure pulse height spectra. The hydrofoil was equipped with eight pressure sensors made of PVDF piezoelectric film that allowed the measurement of flow aggressiveness at different locations along the hydrofoil chord. It was shown that the mean peak rate over a large number of cavity pulsations exhibits a maximum at a distance from the leading edge close to the maximum cavity length. Moreover, the increase in flow aggressiveness caused by an increase in flow velocity can be explained by an increase in both amplitude and frequency of impact loads. From a numerical viewpoint, the unsteady Reynolds averaged Navier-Stokes (RANS) equations were solved using a modified k-ε RNG turbulence model together with a homogeneous cavitation model within a two-dimensional approach. Flow aggressiveness was estimated from the Lagrangian derivative of the computed void fraction that allows identifying the regions of collapse of vapour structures. Three different critical regions from an erosive viewpoint were numerically identified. Apart from the region of collapse of the shed cloud (which was not instrumented in the present study), the computations showed a maximum of aggressiveness around the maximum cavity length as found experimentally. Another region of high aggressiveness closer to the leading edge and associated to the upward movement of the re-entrant jet was predicted by the present numerical model but not confirmed experimentally, which probably shows the limitation of a two-dimensional approach.
The CATHARE-3 predictive transient rotodynamic pump model and its validation in single-phase first quadrant conditions at component scale are presented in this paper. One-dimensional discretization and resolution of governing equations are made according to a mean flow path along all pump parts (suction, impeller, diffuser, volute and discharge pipe), what makes the model original compared to classical 1D models. The model is first verified by comparison to the Euler equation of turbomachinery results. Then, qualification of the model is carried out in steady and transient conditions by comparison to available experimental data. Head and torque characteristics curves are well predicted at different rotational speeds. Finally, a fast startup transient is simulated. Results are satisfactory as the difference between the experimental and modelled non-dimensionalized head is less than 10% of the final value during the whole startup.
Rotor stator interaction in high-head Francis turbines has led to several failures in recent years. Increasing efficiency demands require design optimization of the turbine components, which may lead to thinner profiles. Not only can component not withstand the given loads; quite often one or more of their natural frequencies coincide with that of the rotor-stator interaction. Most of the research published has been on runners, while other parts of the turbine are less studied. Even though guide vanes have torsional modes with frequencies which may be close to the exiting frequency from the rotor stator interaction with the runner, no significant failures due to resonance have been reported. This paper investigates some of the possible mechanisms which may negate resonance in the torsional modes of the guide vanes including; hydrodynamic damping from the flowing water and friction in the guide vane bearings. A case study is conducted on a guide vane where the calculated natural frequency is within 10% of the excitation frequency, while no significant vibrations have been reported. Further, the findings are generalized to Francis turbines of different specific speeds. The results indicate that the dynamics in the bearings are especially important to consider to be able to predict the vibration levels of the guide vane. Having the correct friction factor in the bearing may lead to significant damping and almost eliminate any excitation of torsional eigenmodes.
Technological developments have led to micropumps playing an ever-greater role at the heart of micro total analysis systems. Spiral-channel viscous micropumps have been studied theoretically, numerically, and experimentally. However, high-accuracy performance predictions have not been achieved over a wide range of operating conditions. The present study proposes three-dimensional and quasi-three-dimensional theoretical expressions for predicting the pressure performance of spiral-channel viscous micropumps in low-Reynolds-number environments. The theoretical analysis is validated through a series of comparisons with numerical simulation results for the pressure performance curves, velocity distributions, velocity gradient distributions, and channel internal pressure distributions. Furthermore, the influence of the channel aspect ratio on the performance characteristics is investigated.