Quantification of energy losses at a surcharging manhole

Self Cite

Surcharging urban drainage systems are a potential source of pathogenic contamination of floodwater. While a number of previous studies have investigated net sewer to surface hydraulic flow rates through manholes and gullies during flood events, an understanding of how pollutants move from sewer networks to surface flood water is currently lacking. This paper presents a 3D CFD model to quantify flow and solute mass exchange through hydraulic structures featuring complex interacting pipe and surface flows commonly associated with urban flood events. The model is compared against experimental datasets from a large-scale physical model designed to study pipe/surface interactions during flood simulations. Results show that the CFD model accurately describes pipe to surface flow partition and solute transport processes through the manhole in the experimental setup. After validation, the model is used to elucidate key timescales which describe mass flow rates entering surface flows from pipe networks. Numerical experiments show that following arrival of a well-mixed solute at the exchange structure, solute mass exchange to the surface grows asymptotically to a value equivalent to the ratio of flow partition, with associated timescales a function of the flow conditions and diffusive transport inside the manhole.

Section: Methodsmentioning

confidence: 99%

CFD Modelling of the Transport of Soluble Pollutants from Sewer Networks to Surface Flows during Urban Flood Events

Beg

Rubinato

Carvalho

et al. 2020

Self Cite

“…More recently, the interaction between surface flows versus sewer flows in the manhole structures considering the outflow from the sewer network was studied [31][32][33]. This is the closest reference to the energy loss associated with the outflow from the sewer system, but it investigated the case of sewer overflow when the manhole lid had been removed due to the pressure of the flow, which is associated with specific flooding conditions.…”

Section: Introductionmentioning

confidence: 99%

“…This is the closest reference to the energy loss associated with the outflow from the sewer system, but it investigated the case of sewer overflow when the manhole lid had been removed due to the pressure of the flow, which is associated with specific flooding conditions. In the literature, it was possible to find information about the energy losses in manholes [32], but energy losses associated with grated inlets were not investigated. Moreover, another work developed some 2D numerical simulations of the exchange between a flooded street and its surcharged surface drainage system grates and manholes.…”

Section: Introductionmentioning

confidence: 99%

Quantification of Energy Loss in Two Grated Inlets under Pressure

Alvarez

Gómez

Russo

2020

Grated inlets have the normal function of collecting the surface runoff into sewer networks, but when the flow exceeds the capacity of the sewer pipes and conduits get pressurized, an outflow from the sewer manholes and grates can occur. In this case, the grate produces an energy loss in the outflow from sewer to street that could be hydraulically quantified characterizing this kind of flow. Energy loss analysis in trash racks can be found in technical literature, but no specific studies on sewer grate inlets have been found. For this reason, some experiments in full scale were developed in the hydraulic laboratory of the Technical University of Catalonia (UPC) in order to quantify hydraulic energy losses associated with flow through grated inlets during surcharging conditions. The main goal of this research work was to experimentally quantify the values of the local loss coefficient k for two different surcharged real scale grated inlets existing in Barcelona. For the tested overflows between 20 and 50 L/s, a range from 0.25 to 3.41 was observed for k coefficients under different average velocities of reference and different flow conditions.

“…It typically occurs in hydraulic structures such as manholes, gullies, and gutters due to the presence of pressure flow and can lead to dangerous phenomena like blowout of manhole covers. The flow exchange in manholes between inflow and outflow pipes is complex [21] and the related energy losses are a source of uncertainty in hydraulic models [22]. The energy losses have been investigated in a bend manhole for combined sewer systems [23], in a 45 • junction manhole [24], and under surcharged conditions [25], especially using a scaled physical model [22].…”

Section: Introductionmentioning

confidence: 99%

“…The flow exchange in manholes between inflow and outflow pipes is complex [21] and the related energy losses are a source of uncertainty in hydraulic models [22]. The energy losses have been investigated in a bend manhole for combined sewer systems [23], in a 45 • junction manhole [24], and under surcharged conditions [25], especially using a scaled physical model [22]. Recent progress in understanding energy losses under various flow conditions, especially from physical experiments [26][27][28][29][30], is beneficial for accurate modelling and risk analysis of urban flooding.…”

Section: Introductionmentioning

confidence: 99%

A Simplified Representation of Pressure Flow from Surface Slopes in Urban Sewer Systems

Huang

Pan

Wang

2020

A Constant Pipe Drainage (CPD) capacity for sewer systems is commonly applied when undertaking flood risk assessment, however data that are needed for calibration and validation of numerical models are scarce or unavailable. The CPD model neglects the effect of pressure flow and leads to significant deviation in flood volume estimate. This study proposes a new index Velocity Ratio (VR) to approximate pressure flow. A case study in Guangzhou, China is used to investigate the capability of reproducing a reasonable flood volume for two models, the CPD and the VR-based. Compared to the flood volume simulated by the Storm Water Management Model (SWMM), the CPD model shows a significant overestimation, Mean Relative Deviation (MRD) 192%. The VR-based model has a much better performance, MRD 18%. Therefore, the VR-based model is a simple and effective representation of pressure flow in urban sewer systems and can be easily applied in areas lacking detailed pipe data, especially for planning new pipe networks or updating the old pipes.