Investigation of intrinsic disturbance wave near the end of expiration

1985 ◽  
Vol 5 (3) ◽  
pp. 129-134
Author(s):  
San-cai Zhang
Keyword(s):  
Disturbance Wave

Prediction of the interfacial disturbance wave velocity in vertical upward gas-liquid annular flow via ensemble learning

Energy ◽  
2021 ◽  
pp. 122990
Author(s):  
Chaofan Li ◽  
Yajing Song ◽  
Long Xu ◽  
Ning Zhao ◽  
Fan Wang ◽  
...  
Keyword(s):  
Ensemble Learning ◽  
Wave Velocity ◽  
Annular Flow ◽  
Disturbance Wave

scholarly journals Receptivity of Boundary Layer over a Blunt Wedge due to Freestream Pulse Disturbances at Mach 6

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Jianqiang Shi ◽  
Xiaojun Tang ◽  
Zhenqing Wang ◽  
Mingfang Shi ◽  
Wei Zhao
Keyword(s):  
Boundary Layer ◽  
Fundamental Frequency ◽  
High Frequency ◽  
Pulse Wave ◽  
Second Harmonic ◽  
Acoustic Pulse ◽  
Disturbance Wave ◽  
Acoustic Disturbances ◽  
Disturbance Frequency ◽  
Harmonic Components

Direct numerical simulation (DNS) of a hypersonic compressible flow over a blunt wedge with fast acoustic disturbances in freestream is performed. The receptivity characteristics of boundary layer to freestream pulse acoustic disturbances are numerically investigated at Mach 6, and the frequency effects of freestream pulse wave on boundary layer receptivity are discussed. Results show that there are several main disturbance mode clusters in boundary layer under acoustic pulse wave, and the number of main disturbance clusters decreases along the streamwise. As disturbance wave propagates from upstream to downstream direction, the component of the modes below fundamental frequency decreases, and the component of the modes above second harmonic components increases quickly in general. There are competition and disturbance energy transfer between different boundary layer modes. The nose boundary layer is dominated by the nearby mode of fundamental frequency. The number of the main disturbance mode clusters decreases as the freestream disturbance frequency increases. The frequency range with larger growth narrows along the streamwise. In general, the amplitudes of both fundamental mode and harmonics become larger with the decreasing of freestream disturbance frequency. High frequency freestream disturbance accelerates the decay of disturbance wave in downstream boundary layer.

On the instability of the flow in a squeeze lubrication film

1990 ◽  
Vol 430 (1879) ◽  
pp. 347-375 ◽  
Keyword(s):  
Reynolds Number ◽  
Poiseuille Flow ◽  
Flow Instability ◽  
Initial Distribution ◽  
Neutral Curve ◽  
Time Dependent ◽  
Order Partial Differential Equation ◽  
Plane Poiseuille Flow ◽  
Disturbance Wave ◽  
Sommerfeld Equation

When two parallel plates move normal to each other with a slow time-dependent speed, the velocity field developed in the intervening film of fluid is approximately that of plane Poiseuille flow, except that the magnitude of the velocity is dependent on time and on the coordinate parallel to the planes. This fact is intrinsic to Reynolds’ lubrication theory, and can be shown to follow from the Navier-Stokes equations when both the modified Reynolds number ( Re M ) and an aspect ratio ( δ ) are small. The modified Reynolds number is the product of δ and an actual Reynolds number ( Re ), which is based on the gap between the planes and on a characteristic velocity. The occurrence of flow instability and of turbulence in the film depend on Re . Typical values of Re , which are known to be required for the linear instability of plane Poiseuille flow, are of order 6000. This condition can be achieved, even if Re M is of order 1, provided that δ is of order 10 -4 . Such parameter values are typical of lubrication problems. The Orr-Sommerfeld equation governing flow instability is derived in this paper by use of the WKBJ technique, δ being the approximate small parameter to represent the small length-scale of the disturbance oscillations compared with the larger scale of the basic laminar flow. However, the coefficients in the Orr-Sommerfeld equation depend on slow space and time variables. Consequently the eigenrelation, derivable from the Orr-Sommerfeld equation and the associated boundary conditions, constitutes a nonlinear first-order partial differential equation for a phase function. This equation is solved by use of Charpit’s method for certain special forms of the time-dependent gap between the planes, followed by detailed numerical calculations. The relation between time-dependence and flow instability is delineated by the calculated results. In detail the nature of the instability can be described as follows. We consider a disturbance wave at or near a particular station, the initial distribution of amplitude being gaussian in the slow coordinate parallel to the planes. In the context of the Orr-Sommerfeld equation and its eigenrelation, the particular station implies an equivalent Reynolds number, while the initial distribution of the disturbance wave implies an equivalent wavenumber. As time increases, the disturbance wave can be considered to move in the instability diagram of equivalent wavenumber against Reynolds number, in the sense that these parameters are time- and space-dependent for the evolution of the disturbance-wave system. For our detailed calculations we use a quadratic approximation to the eigenrelation, an approximation which is quite accurate. If the initial distribution implies a point within the neutral curve, when the plates are squeezed together the equivalent wavenumber falls while the equivalent Reynolds number rises, and amplification takes place until the lower branch of the neutral curve is nearly crossed. If the plates are pulled apart (dilatation) the equivalent wavenumber rises, while the Reynolds number drops, and amplification takes place until the upper branch of the neutral curve has been just crossed. In the case of dilatation the transition from amplification to damping takes place more quickly than for the case of squeezing, in part due to the geometry of the neutral curve.

CFD Simulation of Two-Phase Vertical Annular Flow in Both Upward and Downward Direction in a Small Pipe

2019 ◽  
Author(s):  
Ekhwaiter Abobaker ◽  
Abadelhalim Elsanoose ◽  
John Shirokoff ◽  
Mohammad Azizur Rahman
Keyword(s):  
Film Thickness ◽  
Multiphase Flow ◽  
Pressure Gradient ◽  
Annular Flow ◽  
Cfd Simulation ◽  
Flow Direction ◽  
Flow Behavior ◽  
Two Phase ◽  
Downward Flow ◽  
Disturbance Wave

Abstract Computational fluid dynamics (CFD) simulation is presented to investigate the annular flow behavior in the vertical pipe by using ANSYS Fluent platform 17.2. The study was analyzed complex behavior of annular flow in two cases (upward and downward flow) for different air superficial velocities and range of Reynolds number for water, in order to obtain the effect of orientation flow and increasing superficial gas and liquid velocities on the base film, mean disturbance wave thickness, the average longitudinal size of disturbance wave as well as pressure gradient. For multiphase flow model, the volume of fluid method (VOF) for two-phase flow modelling was used and coupled with RNG k-ε turbulence model to predict fully annular flow structures in the upward and downward flow direction. From CFD simulation results, it is clear to see how increases in air velocity result in reductions in film thickness and increase in pressure gradient. Additionally, the results showed monotonic enhancement of film thickness occurring in tandem with increases in the liquid flow rate. However, due to the effect of gravitational force and interfacial friction, the film thickness and pressure gradient are slightly larger for the upward flow than for the downward flow. The results agree with the recent experimental data that studied the annular flow behavior and pressure drop in the upward and downward flow direction. This study will be very helpful in understanding multiphase flow behavior in natural gas wells.

Capillary gravity waves caused by a moving disturbance: Wave resistance

1996 ◽  
Vol 53 (4) ◽  
pp. 3448-3455 ◽  
Author(s):  
E. Raphaël ◽  
P.-G. de Gennes
Keyword(s):  
Gravity Waves ◽  
Wave Resistance ◽  
Disturbance Wave

Generation of Entrained Droplets from an Imitative Disturbance Wave and their Deposition on the Wall

2000 ◽  
Vol 2000.1 (0) ◽  
pp. 813-814
Author(s):  
Tohru FUKANO ◽  
Takanari INATOMI ◽  
Tomohiro YOSHIDA ◽  
Akiharu OUSAKA
Keyword(s):  
Disturbance Wave

K-2203 Generation of Entrained Droplets from an Imitated Disturbance Wave and their Deposition on the Wall

2001 ◽  
Vol V.01.1 (0) ◽  
pp. 263-264
Author(s):  
Tohru FUKANO ◽  
Takanari INATOMI ◽  
Yohei MATSUZAWA ◽  
Tomohiro YOSHIDA
Keyword(s):  
Disturbance Wave
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