Vortex Drop Shaft Structures: State-Of-The-Art and Future Trends (original) (raw)
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Water Science and Technology, 2022
If the operation of existing vortex drop shafts should be verified, then it is essential to know the hydraulic performance of these special structures under both subcritical and supercritical flow regimes. The purpose of the present research consisted of providing practical guidelines and recommendations for managing the hydraulic design and verification of subcritical and supercritical vortex drop shafts. The examination of various experimental results from physical model investigations allowed to show that the inlet channel and the spiral inlet behaved differently depending on the energy approach flow content. The main dissimilarity lay, however, in the functioning of the vertical shaft and the dissipation chamber. The rotation of the falling flow along the vertical shaft was more evident for approaching supercritical flows. Severe flow conditions in terms of water depths and bottom pressures could be observed in the dissipation chamber under a supercritical flow regime. The design of this special component must be carried with prudence compared with the subcritical flow regime because failure events as the chamber submergence and the crash of the bottom surface just under the shaft outlet may occur for approaching supercritical flows.
Hydraulic design aspects for supercritical flow in vortex drop shafts
Urban Water Journal, 2019
Vortex drop shafts, as special sewer manholes, operate optimally if an adequate energy dissipation is guaranteed and the integrity of the structural components is safeguarded. The results of an experimental study on a vortex drop shaft with supercritical inflow are discussed herein. The hydraulic behaviour of the spiral inlet, the vertical shaft and the dissipation chamber is described. Based on detailed flow observations, useful recommendations for designing these structures are provided. It is demonstrated that a relation adopted for supercritical bend flows provides a reliable estimation of the maximum wave height along the inlet. A procedure for predicting the rotational flow angles and the velocity distribution along vertical shafts with swirling flows is developed. Water levels and pressure measurements in the dissipation chamber are further analysed to identify maximum forces acting on the chamber invert and to derive preliminary design equations.
Journal of Structural Integrity and Maintenance
Vortex drop shafts, a key hydraulic structure within modern day deep sewer conveyance systems, must be designed structurally to sustain performance and longevity of operating life under very energetic loading conditions. This has significant cost implications but to date little research has been undertaken to investigate the loading conditions with a view to optimising the shaft designs and thus lowering costs. In this study, several modelling methods were adopted to simulate hydrodynamic conditions within a vortex drop shaft to assess hydrodynamic mechanisms that impact a drop shaft liners structural performance and maintenance. A 1/10 scaled physical hydraulic model of a tangential inlet vortex drop shaft structure is tested and used to validate a threedimensional multiphase numerical model. Collectively, the study presents methods on identifying hydrodynamic phenomena such as pressures, velocities, erosion and abrasion mechanisms, debris impact locations and blocking mechanisms. The study highlighted that the hydrodynamic forces that threaten structural integrity reside in the vortex generator and a short length of the drop shaft downstream. This is shown through a new model developed by the authors to predict centrifugal forces along the length of the drop. Through these methods, the study proposes that drop shaft liners can be designed more efficiently.
Energy Head Dissipation and Flow Pressures in Vortex Drop Shafts
Water
Vortex drop shafts are special manholes designed to link sewer channels at different elevations. Significant energy head dissipation occurs across these structures, mainly due to vertical shaft wall friction and turbulence in the dissipation chamber at the toe of the shaft. In the present study two aspects, sometimes neglected in the standard hydraulic design, are considered, namely the energy head dissipation efficiency and the maximum pressure force in the dissipation chamber. Different physical model results derived from the pertinent literature are analyzed. It is demonstrated that the energy head dissipation efficiency is mostly related to the flow impact and turbulence occurring in the chamber. Similarly to the drop manholes, a relation derived from a simple theoretical model is proposed for the estimation of the energy head loss coefficient. The analysis of the pressures measured on the chamber bottom allows to provide a useful equation to estimate the pressure peak in the ch...
Hydraulics of swirling flows along vortex drop shafts
2020
The vortex drop shaft is a benchmark structure in hydraulic engineering. It is often used in sewers and hydropower systems, given that a significant energy dissipation combined with a reduced space occupation is achieved. Conversely, the flow pattern establishing along the structure may lead to the occurrence of unstable phenomena as vibrations, abrasion and choking, particularly if the operational conditions are different from the standard design regime. It is advantageous to study the overall hydraulic efficiency of the structure, and particularly to derive the hydraulic conditions of the swirling flow along the vertical shaft. At this regard, the paper describes a physically based approach, based on the momentum conservation, to derive the rotational angle and the velocity profiles along the shaft. The method requires the calibration of an empirical parameter accounting for the increase of the wall friction stress due to the centrifugal force. The outcomes of the application of t...
High Head Drop Shaft Structure for Small and Large Discharges
11th International Conference on Urban Drainage
In the early seventies, several high head drop structures were built as part of the construction of the Mexico City deep drainage system. The deep structures solved the problem of connecting the combined sewer system from street level to deep underground tunnels that enabled water discharges from urban areas. As it is common that the space available to build this type of structures is limited, the vertical drop may be several dozen meters, the discharges are extremely variable and it needs to function as sound- and vibration-free as possible; it is therefore necessary to carefully design, test in model and eventually build large drop shafts that take into account all of these conditions. Based on an Italian design (Drioli, 1947), a simpler drop shaft structure was proposed and tested in the late sixties for the Mexico City deep drainage system. It consisted of a spiral entrance that induces a strong vortical movement to achieve the adhesion of the water fall to the pipe walls for both small and large discharges. After more than 35 years of operation, the hydraulic behavior of this drop shaft has been satisfactory. As its characteristics and study results have never been published in English or in an international media, it was considered important to publish them and to highlight the advantages that this type of high head drop shaft has in terms of others found in specialized literature which can be more complicated and expensive.
Investigation of the performance of single and multi-drop hydraulic structures
Journal: Int. J. of Hydrology Science and Technology, 2012 Vol.2, No.1, pp.48 - 74, 2012
In this paper, the work is divided into two parts. First, the hydraulic performance of single and multi-drop structures is investigated and compared using two approaches. In the first approach, the empirical equations found in the literature are summarised and reanalysed to compare the dissipation of energy of single drop and multi-drop structures. The demarcation condition at which multi-drop structure behaves as a single drop is identified. In the second approach, a numerical investigation of the hydraulic performance of single vertical drop and multi-stepped channel has been conducted via the computational fluid dynamic (CFD) fluent package using the volume of fluid (VOF) technique. It is found that the CFD package is able to simulate the hydraulic performance of both structures (single and multi-drop) reasonably well; however, it has been noted that in some situations the CFD package did not detect the presence of air cavities underneath the nappe for the napped flow case. Second, an Excel solver called HSMD has been developed. The objective of this solver is to work as an expert system for the design of drop structures and to facilitate the use of the large number of the available empirical formulas for practicing engineers. A comparison between the previous laboratory empirical formula (adopted in HSMD model) and numerical simulations has been also carried out.
Experimental Study of Flow Energy Residual in a Vortex Drop Structure Using Full Factorial Method
Journal of Water and Wastewater, 2022
One of the basic needs in urban wastewater and drainage systems is the connection of shallow ducts to deep underground tunnels. This connection is usually made through a vortex drop structure. In order to form a vortex flow, in addition to preventing the fluid from falling, a significant part of its energy is lost due to the friction of the walls. In the present study, by constructing a physical model, the residual energy head in the structure (ratio of specific energy at the output (E2) to specific energy at the input of the structure, (E1)) has been studied. Using dimensional analysis of dimensionless factors of Froude number (Fr), the ratio of total fall height to shaft diameter (L⁄D) and the ratio of sump depth to shaft diameter (Hs ⁄D) were determined as factors affecting the residual energy head in the structure. Using experimental observations, the accuracy and capability of the full factorial method to describe the residual flow energy in the structure were evaluated. The results showed that the residual energy head for the Froude number corresponding to the design flow discharge at Fr=2.18 is closest to the limit value of 1. On the other hand, for all L/D operating levels, the residual energy head values are close to 1. Moreover, the smallest difference between the values of the residual energy head and the limit value was 1 for Hs/D values between 1 and 2, indicating suitable range for the practical purpose. In addition, a polynomial equation as a function of Fr, L⁄D and Hs ⁄D was expressed to accurately estimate the residual energy head in the vortex, drop structure using regression analysis.
Junction Chamber at Vortex Drop Shaft: Case Study of Cossonay
2016
The drainage network of the city of Cossonay (Switzerland) is currently being adapted for future needs. In particular, it is required to drain increased storm discharges due to a population augmentation and to provide an adequate concept to overcome unfavorable geotechnical conditions. Vortex drop shafts are sewer manholes commonly applied in steep urbanized topographies to connect conduits across large elevation differences. In Cossonay, the existing 48 m high vortex drop shaft, with a diameter of 1.5 m, allowed the storm discharge to flow from the city to a watercourse issued at half of the valley height. The discharge capacity was initially assumed as 4.1 m3/s, but frequent pulsations and choking phenomena implied a reduced effective capacity of around 3.0 m3/s. A new planned vortex drop shaft will collect the supercritical inflows of four collectors in the old City Centre and spill them through a shaft of roughly 120 m height, restituting the flow at the valley bottom. It was pr...
Modelling for Simplified Vortex Manhole
International journal of engineering research and technology, 2017
Vortex drop manhole has been improved to solve number of problems associated with conventional drop systems. It dissipates the flow energy, protecting the drop structure from intensive corrosion and abrasive wear. The aim of this present study is to investigate the hydraulic performance of a simplified eccentric vortex drop shaft in order to keep the configuration of vortex shaft elements as simple as possible to facilitate its construction and minimize the construction and maintenance cost ,at the same time be ensured that the vortex shaft hydraulically efficient and stable. Two models have been constructed to investigate the use of centric and eccentric vertical shaft. Results showed that the use of eccentric chamber reduces the vortex chamber height by 25% and it is allowed to pass 19% flow rates more than the centric chamber. Results also showed that the eccentric shaft rises the dissolved oxygen concentration by 14% than the centric shaft at the maximum discharge. In addition, decreasing the enlargement angle from 270º to 220º increasing the amount of flow rate passing through the shaft by 18% and decreasing the water depths above the vortex channel by 29%.