On the Propagation and Attenuation of Turbulent Fluid Transients in Circular Pipes

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
E. M. Wahba
Keyword(s):  
Pressure Rise ◽  
Pressure Head ◽  
Turbulent Fluid ◽  
Nondimensional Parameter ◽  
Runge Kutta Method ◽  
Circular Pipes ◽  
Fluid Transients ◽  
1D Model ◽  
Second Category ◽  
Packing Effects

The attenuation of turbulent fluid transients in pipes is numerically investigated in the present study using one-dimensional (1D) and two-dimensional (2D) water hammer models. The method of characteristics (MOC) is used for the integration of the 1D model, while the semidiscretization approach and the fourth-order accurate Runge–Kutta method are used for the integration of the 2D model. The present results for a reservoir–pipe–valve system indicate that the damping of the transient is governed by a nondimensional parameter representing the ratio of the steady-state frictional head to the Joukowsky pressure head. Based on this parameter, the attenuation of the transient could be classified into three main categories. The first category is for values of the nondimensional parameter much smaller than unity, where attenuation of the transient is insignificant and line packing effects are negligible. The second category is for values of the parameter approaching unity, where the attenuation of the transient is significant and line packing results in a pressure rise at the valve that is slightly higher than the Joukowsky pressure rise. The third category is for values of the parameter much greater than unity, such as in long cross-country pipelines, where the transient is damped out within a few cycles and excessive line packing effects would result in a pressure rise at the valve that is significantly larger the Joukowsky pressure rise.

Charts for water hammer in low head pump discharge lines resulting from water column separation and check valve closure

1984 ◽  
Vol 11 (4) ◽  
pp. 717-742 ◽  
Author(s):  
Eugen Ruus ◽  
Bryan Karney ◽  
Farouk A. El-Fitiany
Keyword(s):  
Water Column ◽  
Pressure Rise ◽  
Check Valve ◽  
Pressure Head ◽  
Maximum Pressure ◽  
Valve Closure ◽  
High Point ◽  
Column Separation ◽  
Discharge Line ◽  
Low Head

Maximum pressure head rises resulting from water column separation and check valve closure are calculated and plotted for a simple low head pump discharge line with one well-defined high point. Basic parameters such as pipeline constant, pipe wall friction, complete pump characteristics, pump inertia constant, and the relative location of the high point are accounted for in the analyses. The results of this paper can be used to determine (a) when water column separation is expected, (b) how to avoid water column separation, and (c) the necessary wall thickness in cases where no protection against water column separation is provided. Computer studies indicate that both the vertical and horizontal location of the high point as well as the pipe friction, the pipeline constant, and the pump inertia have a major effect on pressure head rises. Water column separation does not always constitute a danger to the pipeline. Key words: waterhammer, water column separation, check valve closure, pressure rise, pump discharge line, chart.

scholarly journals Vadose Zone Modeling in a Small Forested Catchment: Impact of Water Pressure Head Sampling Frequency on 1D-Model Calibration

Geosciences ◽  
2018 ◽  
Vol 8 (2) ◽  
pp. 72 ◽  
Author(s):  
Benjamin Belfort ◽  
Ivan Toloni ◽  
Philippe Ackerer ◽  
Solenn Cotel ◽  
Daniel Viville ◽  
...  
Keyword(s):  
Vadose Zone ◽  
Model Calibration ◽  
Water Pressure ◽  
Pressure Head ◽  
Sampling Frequency ◽  
Forested Catchment ◽  
1D Model ◽  
Zone Modeling

Transient conditions in the transition from gravity to surcharged sewer flow

1982 ◽  
Vol 9 (2) ◽  
pp. 189-196 ◽  
Author(s):  
M. A. Hamam ◽  
J. A. McCorquodale
Keyword(s):  
Transition Period ◽  
Flow Instability ◽  
Pressure Rise ◽  
Pressure Head ◽  
Gravity Flow ◽  
Relative Depth ◽  
Pipe Material ◽  
Two Phase ◽  
Pressure Flow ◽  
Adequate Treatment

One of the least understood aspects of flow in sewers is the nature of the transition from gravity to pressure or surcharged flow. A complete design of a storm sewer should consider both gravity and surcharged conditions. The available design and/or simulation models can handle gravity (open-channel) flow with various degrees of sophistication, whereas some consider surcharged flow. None of the available stormwater computer models include an adequate treatment of the transient pressures associated with surges that can occur at the transition from gravity to pressure flow. During the transition period there is a further complication because there is a mixture of air and water in the pipe.This paper deals with transients that occur when gravity flow is suddenly changed to pressure flow by the occurrence of a surge in the line. The pressure head fluctuations associated with this transient have been studied. Some of the factors affecting the pressure transients are: pipe size, pipe shape, flow velocity, Froude number, relative depth of flow, alignment of the pipe, pipe material, venting arrangements, and boundary conditions such as pumps, interceptors, and drop pipes. The paper also suggests a theory to predict the excess pressure rise due to these transients. Keywords: Fluid transients, gravity flow, instability, pipe flow, sewers, surcharged flow, surges, two-phase flow.

Analysis of the Design Bounds in Performance Limits for Industrial Axial Flow Fans

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Gabriele Milanese
Keyword(s):  
Flow Characteristics ◽  
Axial Flow ◽  
Pressure Rise ◽  
Design Flow ◽  
Preliminary Design ◽  
Performance Limits ◽  
Flow Topology ◽  
Static Efficiency ◽  
Axial Fans ◽  
1D Model

Abstract The design of an industrial axial flow fan can take great advantage from the knowledge of performance limits and favourable design choices determined from its specific fluid-dynamic characteristics. As for other turbomachinery types, this fact is generally experienced through the entire design flow-path, from the preliminary design phase to the final optimization. Correlations, data and charts available from literature as well as proprietary database, exploited with many techniques (including machine learning) are resources in widespread use for this purpose. Despite the fluid dynamics of axial flow fans can be considered a well-known topic, nevertheless some specific points (e.g. the maximum achievable total-to-static efficiency) can be the subject of discussions, misunderstanding or bad design choices. The present work addresses this problem in two parts. In the first part a simple 1D model is built, for fans with and without stator, from classical theory of axial fans for pressure rise coefficient, head coefficient, flow angles and diffusion efficiency. The most relevant quantities (e.g. total-to-total efficiency, total-to-static efficiency), obtained with the 1D model, are plotted on hill charts as a function of the non-dimensional pressure rise and flow coefficient. This tool provides information that can be used for preliminary design evaluations, to understand and exploit the impact of the main design choices on the basic flow characteristics and the related performance. In the second part of the work a numerical investigation is presented on the main 3D flow characteristics that are observed to limit, both in CFD simulations and experimental tests, the performance of industrial axial fans at high-pressure rise and low-to-medium flow coefficients. Simulations results highlighted that local critical swirl ratios exist for the hub and the tip regions which, when exceeded, lead with different flow topology changes to a strong performance degradation.

Valve Stroking to Control Water Hammer Transients Using Dynamic Programming

1987 ◽  
Vol 109 (1) ◽  
pp. 94-100 ◽  
Author(s):  
D. N. Contractor
Keyword(s):  
Dynamic Programming ◽  
Pressure Rise ◽  
The Other ◽  
Valve Closure ◽  
Time Period ◽  
Fluid Transients ◽  
Valve Opening ◽  
Closure Policy ◽  
Valve Operation ◽  
Control Water

Fluid transients in a pipeline caused by valve operation can be minimized by operating the valve in an optimally prescribed manner, in a given time of closure (tc > 2L/a). Dynamic programming is used to select the operation of the valve (i.e., set the valve-operating policy) over the time period tc so that the pressure rise at the valve (the objective function) is minimized. Constraints on the valve closure policy may also be specified, e.g., monotonic valve closure. Application of this method to a simple pipeline with a reservoir at one end and a valve at the other end shows that the pressure rise at the valve is lower than when the valve is closed linearly with time. The benefits of dynamic programming are shown to be greatest when the time of closure tc is small. The method has also been applied to valve opening, so that the pressure drop at the valve is a minimum.

Effect of apraclonidine hydrochloride on acute introacular pressure rise after argon laser iridotomy

1991 ◽  
Vol 5 (1) ◽  
pp. 37 ◽  
Author(s):  
Chul Hong ◽  
Ki Yung Song ◽  
Woo Hyung Park ◽  
Young Ho Sohn
Keyword(s):  
Pressure Rise ◽  
Argon Laser ◽  
Laser Iridotomy

Fundamental Examination of Numerical Simulation Model for Pressure Rise due to Underwater Arc

2014 ◽  
Vol 134 (7) ◽  
pp. 604-613 ◽  
Author(s):  
Toshiya Ohtaka ◽  
Tomo Tadokoro ◽  
Masashi Kotari ◽  
Tadashi Amakawa
Keyword(s):  
Numerical Simulation ◽  
Simulation Model ◽  
Pressure Rise
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