Predicting Non-Linear Flow Phenomena through Different Characteristics-Based Schemes

Teschner, Tom-Robin; Könözsy, László; Jenkins, Karl W.

doi:10.3390/aerospace5010022

Cited by 4 publications

(2 citation statements)

References 36 publications

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“…More than 200 papers were retrieved by database searches for 2015-2020 using the terms artificial compressibility, pseudo compressibility, and dual time stepping. These studies include analysis of the relationships between AC and fractional step methods [86,87], studies of turbulent flow [88][89][90], development of discontinuous Galerkin methods [91][92][93], parallel solution of large-scale problems [94][95][96], multi-fluid simulations [97], further advances to entropically-damped AC methods [98][99][100], implementation high-order numerical schemes [101][102][103], use of characteristic methods [104][105][106], application for non-hydrostatic effects [107,108], magneto-hydrodynamic simulations [109][110][111], solution with lattice Boltzmann methods [112], and solution by smoothed particle hydrodynamics [113,114]. Note the above are examples and should not be considered an exhaustive list of recent work.…”

Section: Recent Development Of the Artificial Compressibility Methodsmentioning

confidence: 99%

An Artificial Compressibility Method for 1D Simulation of Open-Channel and Pressurized-Pipe Flow

Hodges

2020

Water

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Piping systems (e.g., storm sewers) that transition between free-surface flow and surcharged flow are challenging to model in one-dimensional (1D) networks as the continuity equation changes from hyperbolic to elliptic as the water surface reaches the pipe ceiling. Previous network models are known to have poor mass conservation or unpredictable convergence behavior at such transitions. To address this problem, a new algorithm is developed for simulating unsteady 1D flow in closed conduits with both free-surface and surcharged flow. The shallow-water (hydrostatic) approximation is used as the governing equations. The artificial compressibility (AC) method is implemented as a dual-time-stepping discretization for a finite-volume solver with timescale interpolation used for face reconstruction. A new formulation for the AC celerity parameter is proposed such that the AC celerity matches the equivalent gravity wave speed for the local hydraulic head—which has some similarities to the classic Preissmann Slot used to approximate pressurized flow in conduits. The new approach allows the AC celerity to be set locally by the flow (i.e., non-uniform in space) and removes it as a free parameter of the AC solution method. The derivation of the AC method provides for only a minor change in the form of the solution equations when a computational element switches from free-surface to surcharged. The new solver is tested for both unsteady free-surface (supercritical, subcritical) and surcharged flow transitions in a circular pipe and is implemented in an open-source Python code available under the name “PipeAC.” The results are compared to laboratory experiments that include rapid flow changes due to opening/closing of gates. Results show that the new algorithm is satisfactory for 1D representation of unsteady transition behavior with two caveats: (i) sufficient grid resolution must be applied, and (ii) the shallow-water equation approximations (hydrostatic, single-fluid) limit the accuracy of the solution with regards to the celerity of the turbulent unsteady bore that propagates upstream. This research might benefit any piping network model that must smoothly handle unsteady transitions from free surface to surcharged flow.

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Section: Recent Development Of the Artificial Compressibility Methodsmentioning

confidence: 99%

An Artificial Compressibility Method for 1D Simulation of Open-Channel and Pressurized-Pipe Flow

Hodges

2020

Water

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“…Teschner et al [14] simulated Navier-Stokes equations numerically. They used characteristic based schemes Rusanov's Riemann solver to treat the convective term through a Godunov-type method.…”

Section: Introductionmentioning

confidence: 99%

Laminar Forced Convection Simulation at Different Boundary Conditions with Averaging Scheme (Numerical and Theoretical Research)

Adibi¹,

Adibi²

2019

MMEP

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In this paper, cavity flow is simulated numerically. Forced convection in different Reynolds numbers between 100 and 5000 is simulated. Different and complex thermal boundary conditions are applied and various parameters are calculated numerically. Up and down walls are in constant temperature and left and right walls are thermal insulation in the first thermal boundary condition. The Left and the down walls are in constant temperature and the temperature of the up and the right walls changes linearly in the second thermal boundary condition. For the third thermal boundary condition, the left and the down walls are in constant temperature and the temperature of the up and the right walls changes sinusoidally. For this purpose, a code is written in the FORTRAN software. Streamlines, isotherms, local and mean Nusselt number are obtained and shown in different figures and one table. Grid independence is surveyed and some obtained results are validated with other researchers' work. In these simulations, the Prandtl number is considered to be 0.71 because of the air's Prandtl number. For time discretization, a fifth-order Runge-Kutta is used and for convective fluxes, the averaging scheme with fourth-order damping term is used.

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Arrival time estimation methodology for partial discharge acoustic signals in power transformers based on a double-threshold technique

Wang

Fan

Qin³

et al. 2018

Meas. Sci. Technol.

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Much attention has been paid to different localisation algorithms to locate partial discharge (PD) sources in power transformers using the acoustic emission (AE) technique. Due to total reflection, AE sensors cannot always detect the signal of a direct wave. As a result, localisation algorithms based on an indirect wave can be more accurate. But little research has addressed arrival time (AT) methods of indirect PD signals. In this paper, a double-threshold (DT) method is introduced, and its improvement based on short-time energy and a zero-crossing rate is described. Because an indirect wave arrives earlier and has lower energy than a direct wave, current AT methods, such as the energy criterion, cross-correlation, and linear prediction residual methods, cannot determine its AT. However, the proposed DT method can determine the AT precisely. Moreover, a localisation experiment was conducted on a 35 kV transformer, and localisation results were calculated employing various AT methods and different localisation algorithms, such as the Chan, genetic, imperial competition, and improved-propagation-route-search algorithms. Characteristics of the proposed AT methods were compared and analysed to show their feasibility and accuracy.

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Predicting Non-Linear Flow Phenomena through Different Characteristics-Based Schemes

Cited by 4 publications

References 36 publications

An Artificial Compressibility Method for 1D Simulation of Open-Channel and Pressurized-Pipe Flow

An Artificial Compressibility Method for 1D Simulation of Open-Channel and Pressurized-Pipe Flow

Laminar Forced Convection Simulation at Different Boundary Conditions with Averaging Scheme (Numerical and Theoretical Research)

Arrival time estimation methodology for partial discharge acoustic signals in power transformers based on a double-threshold technique

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