Numerical Investigation of the Pressure-Time Method Considering Pipe With Variable Cross Section

被引:8
|
作者
Saemi, Simindokht [1 ,2 ]
Raisee, Mehrdad [3 ]
Cervantes, Michel J. [2 ]
Nourbakhsh, Ahmad [3 ]
机构
[1] Univ Tehran, Coll Engn, Sch Mech Engn, Tehran 1439955961, Iran
[2] Lulea Univ Technol, Div Fluid & Expt Mech, SE-97187 Lulea, Sweden
[3] Univ Tehran, Coll Engn, Sch Mech Engn, Hydraul Machinery Res Inst, Tehran 1439955961, Iran
来源
JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME | 2018年 / 140卷 / 10期
关键词
pressure-time method; variable cross section; flow rate calculation; transient analysis; CFD; FRICTION-FACTOR; TURBULENCE DYNAMICS; WALL FRICTION; FLOW; MODEL; EQUATION;
D O I
10.1115/1.4040718
中图分类号
TH [机械、仪表工业];
学科分类号
0802 ;
摘要
A common method to calculate the flow rate and consequently hydraulic efficiency in hydropower plants is the pressure-time method. In the present work, the pressure-time method is studied numerically by three-dimensional (3D) simulations and considering the change in the pipe cross section (a contraction). Four different contraction angles are selected for the investigations. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and the low-Reynolds k-omega shear stress transport (SST) turbulence model are used to simulate the turbulent flow. The flow physics in the presence of the contraction, and during the deceleration period, is studied. The flow rate is calculated considering all the losses: wall shear stress, normal stresses, and also flux of momentum in the flow. The importance of each term is evaluated showing that the flux of momentum plays a most important role in the flow rate estimation while the viscous losses term is the second important factor. To extend the viscous losses calculations applicability to real systems, the quasi-steady friction approach is employed. The results showed that considering all the losses, the increase in the contraction angle does not influence the calculated errors significantly. However, the use of the quasi-steady friction factor introduces a larger error, and the results are reliable approximately up to a contraction angle of theta = 10 deg. The reason imparts to the formation of a local recirculation zone upstream and inside the contraction, which appears earlier as the contraction angle increases. This feature cannot be captured by the quasi-steady friction models, which are derived based on the fully developed flow assumption.
引用
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页数:15
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