scholarly journals Damping in Transient Pressurized Flows

2019 ◽  
Vol 145 (10) ◽  
pp. 04019034 ◽  
Author(s):  
Sahad Khilqa ◽  
Mohamed Elkholy ◽  
Mohammed Al-Tofan ◽  
Juan M. Caicedo ◽  
M. Hanif Chaudhry
Keyword(s):  
Pressurized Flows

Transient Analysis of Mixed Free-Surface-Pressurized Flows With Modified Slot Model: Part 2 — Similarity Law and Eigenvalue Problem

2003 ◽  
Author(s):  
Kazutoshi Arai ◽  
Katsuhiro Yamamoto ◽  
Mitsuhiro Saitou ◽  
Shigeru Fukumoto
Keyword(s):  
Free Surface ◽  
Differential Equations ◽  
Numerical Solutions ◽  
Transient Flow ◽  
Pressure Rise ◽  
Complex Eigenvalue ◽  
Velocity Difference ◽  
Model Calculations ◽  
Pressurized Flows ◽  
Entrapped Air

To analyze transient free-surface-pressurized flows with entrapped air in a drainage system, a virtual slot model with ceiling has been introduced. Using this model, calculations for the reduced model and the actual size model are carried out to examine a scale effect on the transient flow. The results show that up-scaling the system causes the increase in compressibility of entrapped air so that the rate of pressure rise decreases. Next, it is confirmed that the partial differential equations for the modified slot model have real eigenvalues and then the initial value problem is well-posed when the velocity difference between air and water is not so large. The increase in the velocity difference yields a system having complex eigenvalue, however the well behaved numerical solutions can be obtained since the friction terms in the differential equations suppress the numerical instability.

scholarly journals Suppress Numerical Oscillations in Transient Mixed Flow Simulations with a Modified HLL Solver

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1245 ◽  
Author(s):  
Zhonghao Mao ◽  
Guanghua Guan ◽  
Zhonghua Yang
Keyword(s):  
Acoustic Wave ◽  
Wave Speed ◽  
Hydraulic Systems ◽  
Simple Method ◽  
Flow Simulations ◽  
Flow Regime Transition ◽  
Pressurized Flows ◽  
Numerical Oscillations ◽  
Two Parameters ◽  
Good Agreement

Transition between free-surface and pressurized flows is a crucial phenomenon in many hydraulic systems. During simulation of such phenomenon, severe numerical oscillations may appear behind filling-bores, causing unphysical pressure variations and computation failure. This paper reviews existing oscillation-suppressing methods, while only one of them can obtain a stable result under a realistic acoustic wave speed. We derive a new oscillation-suppressing method with first-order accuracy. This simple method contains two parameters, Pa and Pb, and their values can be determined easily. It can sufficiently suppress numerical oscillations under an acoustic wave speed of 1000 ms−1. Good agreement is found between simulation results and analytical results or experimental data. This paper can help readers to choose an appropriate oscillation-suppressing method for numerical simulations of flow regime transition under a realistic acoustic wave speed.

scholarly journals 515 Influence of Initial Depth of Water on Transient Free-Surface-Pressurized Flows

2001 ◽  
Vol 2001.7 (0) ◽  
pp. 189-190
Author(s):  
Kazutoshi ARAI ◽  
Sinya MORI ◽  
Katsuhiro YAMAMOTO
Keyword(s):  
Free Surface ◽  
Pressurized Flows
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