Numerical investigation of self-oscillatory flows in the rotation channels with cylindrical bodies on the axis

2019 ◽  
Author(s):  
В.И. Пинчуков
Keyword(s):  
Shock Waves ◽  
Compressible Flows ◽  
Turbulent Viscosity ◽  
Computational Modelling ◽  
Unsteady Flows ◽  
Cylindrical Body ◽  
Flow Equations ◽  
Numerical Studies ◽  
Contact Discontinuities ◽  
Original Class

Работа посвящена поиску новых автоколебательных течений и их численному изучению. Эти поиски проводились путем расчетных исследований течений с максимальным количеством контактных разрывов и точек пересечения разрывов ударных волн с ударными волнами или ударных волн с контактными разрывами. Рассмотрены два класса течений: натекание звуковой недорасширенной струи на цилиндрическое тело, расположенное в открытой трубе, и взаимодействие сверхзвукового однородного потока с системой открытый канал вращения (с переменным сечением) цилиндрическое тело на оси. В обоих случаях найдены автоколебательные режимы. Двумерные осесимметричные уравнения сжимаемого газа решены с помощью неявной схемы РунгеКутты третьего порядка. Применяется алгебраическая турбулентная вязкость, основанная на использовании обобщенной формулы Кармана. This paper addresses a search for new selfoscillatory compressible flows and numerical studies of these flows. These searches are carried out by computational modelling of currents with the maximum number of contact discontinuities and points of intersection of discontinuities shock waves with shock waves or shock waves with contact discontinuities. Two families of unsteady flows are considered. The first one contains flows near underextended sonic jets, impinging on cylindrical bodies placed in open tubes. The second family corresponds to interactions of uniform supersonic streams with pairs containing the open channel of rotation (with transient crossection) and a cylindrical body on the axis. Selfoscillatory regimes are found in both cases. Twodimensional axysimmetrical compressble flow equations are solved by an implicit RungeKutta scheme of the third order. Algebraic turbulent viscosity is assumed which is based on the implementation of the generalized Karman formulae. Numerical results allow concluding that unsteady flows, which take place when sonic jets impinge on a pair containing of cylinders and open tubes are typical for jets impinging on obstacles. Flows, which take place when uniform streams interact with these pairs comprise a new original class of selfoscillatory flows.

Modified Governing Equations for Unsteady Compressible Flow in Ducts

1978 ◽  
Vol 45 (4) ◽  
pp. 723-726 ◽  
Author(s):  
A. Celmin¸sˇ
Keyword(s):  
Compressible Flow ◽  
Power Law ◽  
Unsteady Flows ◽  
Tube Flow ◽  
Axially Symmetric ◽  
Governing Equations ◽  
Flow Equations ◽  
Circular Tubes ◽  
First Order ◽  
General Conservation

Conventional governing equations for unsteady compressible tube flows are reviewed and it is shown that they neglect first-order terms which can have significant magnitudes. The derivation of correct tube flow equations from general conservation laws is demonstrated for the case of axially symmetric straight tubes. The traditionally neglected terms are computed explicitly for unsteady flows with power law profiles through circular tubes.

Numerical Study of the Pressure Drop in a Flame Arrestor Using a Porous Media Model

2020 ◽  
Author(s):  
Hoden A. Farah ◽  
Frank K. Lu ◽  
Jim L. Griffin
Keyword(s):  
Numerical Simulation ◽  
Porous Media ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Small Scale ◽  
Forchheimer Equation ◽  
Flow Equations ◽  
Numerical Studies ◽  
Porous Media Model ◽  
Empirical Coefficients

Abstract A numerical study of the flow characteristics of a crimped flame arrestor element was conducted using a porous media model. The porous zone was modeled using the Forchheimer equation. The Forchheimer equation was incorporated into the governing conservation equations as a momentum sink. A small-scale crimped flame arrestor element was tested to determine the empirical coefficients in the Forchheimer equation. The numerical simulation result using this porous media model was verified using experimental data. The flow characteristics of a four-inch detonation flame arrestor with the same crimp design as the small-scale sample, was simulated using the porous media model. The numerical simulation flow data were compared against experimental values and agreed to within five percent. The method used to determine the Forchheimer coefficients and the experimental test setup are described in detail. The application of the Forchheimer equation into the governing flow equations is presented. The challenges and limitation of numerical studies in flame arrestors applications are discussed. The simplification gained by using the porous media model in flame arrestor numerical studies is presented.

The admissibility domain of rarefaction shock waves in the near-critical vapour–liquid equilibrium region of pure typical fluids

2016 ◽  
Vol 795 ◽  
pp. 241-261 ◽  
Author(s):  
Nawin R. Nannan ◽  
Corrado Sirianni ◽  
Tiemo Mathijssen ◽  
Alberto Guardone ◽  
Piero Colonna
Keyword(s):  
Shock Waves ◽  
Critical Point ◽  
Compressible Flows ◽  
Three Dimensional ◽  
Fundamental Equation ◽  
Phase Region ◽  
Liquid Equilibrium ◽  
Two Phase ◽  
Rarefaction Shock ◽  
Equilibrium Region

Application of the scaled fundamental equation of state of Balfour et al. (Phys. Lett. A, vol. 65, 1978, pp. 223–225) based upon universal critical exponents, demonstrates that there exists a bounded thermodynamic domain, located within the vapour–liquid equilibrium region and close to the critical point, featuring so-called negative nonlinearity. As a consequence, rarefaction shock waves with phase transition are physically admissible in a limited two-phase region in the close proximity of the liquid–vapour critical point. The boundaries of the admissibility region of rarefaction shock waves are identified from first-principle conservation laws governing compressible flows, complemented with the scaled fundamental equations. The exemplary substances considered here are methane, ethylene and carbon dioxide. Nonetheless, the results are arguably valid in the near-critical state of any common fluid, namely any fluid whose molecular interactions are governed by short-range forces conforming to three-dimensional Ising-like systems, including, e.g. water. Computed results yield experimentally feasible admissible rarefaction shock waves generating a drop in pressure from 1 to 6 bar and pre-shock Mach numbers exceeding 1.5.

scholarly journals Convergence Region of Newton Iterative Power Flow Method: Numerical Studies

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Jiao-Jiao Deng ◽  
Hsiao-Dong Chiang
Keyword(s):  
Power Flow ◽  
Test System ◽  
Initial Guess ◽  
Fractal Boundary ◽  
Convergence Region ◽  
Nonlinear Load ◽  
Flow Equations ◽  
Flow Method ◽  
Numerical Studies ◽  
Power Flow Method

Power flow study plays a fundamental role in the process of power system operation and planning. Of the several methods in commercial power flow package, the Newton-Raphson (NR) method is the most popular one. In this paper, we numerically study the convergence region of each power flow solution under the NR method. This study of convergence region provides insights of the complexity of the NR method in finding power flow solutions. Our numerical studies confirm that the convergence region of NR method has a fractal boundary and find that this fractal boundary of convergence regions persists under different loading conditions. In addition, the convergence regions of NR method for power flow equations with different nonlinear load models are also fractal. This fractal property highlights the importance of choosing initial guesses since a small variation of an initial guess near the convergence boundary leads to two different power flow solutions. One vital variation of Newton method popular in power industry is the fast decoupled power flow method whose convergence region is also numerically studied on an IEEE 14-bus test system which is of 22-dimensional in state space.

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