On 2D Liquid Sheet Atomization

2006 ◽  
Author(s):  
Frederic Couderc ◽  
Jean-Luc Estivalezes
Keyword(s):  
Boundary Layer ◽  
Physical Phenomenon ◽  
Experimental Studies ◽  
Maximum Amplitude ◽  
Liquid Sheet ◽  
Linear Stability Theory ◽  
Complete Agreement ◽  
Two Dimensional ◽  
Air Velocity ◽  
Global Oscillation

Liquid sheet atomization by coflowing air flows appears in a broade range of industrial process, but still remains not well understood. This paper is devoted to the numerical investigation of the air-assisted disintegration of a planar liquid sheet by two parallel air streams flowing on both sides. To do that, a DNS solver for two-phase incompressible viscous flows with interface capturing feature for non miscible fluids has been developped and validated [1]. The interface is captured by a Level-Set method, which has become very popular during the last ten years. However, unlike classical approaches, stress tensor jump conditions across the interface are explicitly taken into account without introducing any smoothing. Although the physical phenomenon is tridimensional, experimental studies show that the initial stage of the liquid sheet oscillations is mainly two-dimensional which justifies the two dimensional simulations done in this paper. We present a first two-dimensional spatial simulation which shows the gas flow dynamics in interaction with the liquid sheet oscillations. By separation of the air boundary layer behind the liquid sheet at its maximum amplitude location, vortical structures are created and evolve in time with the frequency of the liquid sheet global oscillation. We investigate the effects of the main flow parameters such as outer air velocity, air boundary layer thickness on the main characteristics of the flow and the global oscillation frequency. The first result from our study concerning the frequency oscillation shows a linear variation of the frequency with air velocity. This is in complete agreement with experimental results of [2], whereas inviscid linear stability theory predicts a quadratic evolution. Evidence from those results shows that two-dimensional spatial simulations can provided relevant information on the early stage of liquid sheet atomization.

The development of a two-dimensional wavepacket in a growing boundary layer

1982 ◽  
Vol 384 (1787) ◽  
pp. 317-332 ◽  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Linear Stability ◽  
Stability Theory ◽  
Linear Stability Theory ◽  
Two Dimensional ◽  
Displacement Thickness ◽  
Power Comparisons ◽  
The One ◽  
Half Power

The evolution of a two-dimensional wavepacket in a growing boundary layer is discussed in terms of linear stability theory. The wavepacket is represented by an integral of periodic wavetrains, each of which is defined as a series in terms of the inverse of the local displacement thickness Reynolds number to the one half power. Comparisons are made between the waveforms computed directly from the integral, a steepest-descent expansion of the integral, and a global expansion about the peak of the wavepacket.

scholarly journals Longitudinal instabilities in an air-blasted liquid sheet

2001 ◽  
Vol 437 ◽  
pp. 143-173 ◽  
Author(s):  
ANTONIO LOZANO ◽  
FÉLIX BARRERAS ◽  
GUILLERMO HAUKE ◽  
CÉSAR DOPAZO
Keyword(s):  
Boundary Layer ◽  
Oscillation Frequency ◽  
Numerical Study ◽  
Near Field ◽  
Interface Velocity ◽  
Liquid Sheet ◽  
Linear Instability ◽  
Air Velocity ◽  
Instability Analysis ◽  
Sheet Breakup

An experimental and numerical study has been performed to improve the understanding of the air/liquid interaction in an air-blasted breaking water sheet. This research is focused in the near field close to the exit slit, because it is in this region where instabilities develop and grow, leading to the sheet breakup. In the experiments, several relevant parameters were measured including the sheet oscillation frequency and wavelength, as well as the droplet size distribution and the amplification growth rate. The flow was also investigated using linear instability theory. In the context of existing papers on instability analysis, the numerical part of this work presents two unique features. First, the air boundary layer is taken into account, and the effects of air and liquid viscosity are revealed. Second, the equations are solved for the same parameter values as those in the experiments, enabling a direct comparison between calculations and measurements; although qualitatively the behaviour of the measured variables is properly described, quantitative agreement is not satisfactory. Limitations of the instability analysis in describing this problem are discussed. From all the collected data, it is confirmed that the oscillation frequency strongly depends on the air speed due to the near-nozzle air/water interaction. The wave propagates with accelerating interface velocity which in our study ranges between the velocity of the water and twice that value, depending on the air velocity. For a fixed water velocity, the oscillation frequency varies linearly with the air velocity. This behaviour can only be explained if the air boundary layer is considered.

scholarly journals Separated rows structure of vortex streets behind triangular objects

2019 ◽  
Vol 862 ◽  
pp. 216-226
Author(s):  
Ildoo Kim
Keyword(s):  
Boundary Layer ◽  
Thin Layer ◽  
Boundary Layers ◽  
Experimental Studies ◽  
Soap Film ◽  
Separation Distance ◽  
Two Dimensional ◽  
Spatial Structures ◽  
Physical Mechanisms ◽  
Vortex Streets

We discuss two distinct spatial structures of vortex streets. The ‘conventional mushroom’ structure is commonly discussed in many experimental studies, and the exotic ‘separated rows’ structure is characterized by a thin layer of irrotational fluid between two rows of vortices. In a two-dimensional soap film channel, we generate the exotic vortex arrangement by using triangular objects. This setting allows us to vary the thickness of boundary layers and their separation distance independently. We find that the separated rows structure appears only when the boundary layer is thinner than 40 % of the separation distance. We also discuss two physical mechanisms of the breakdown of vortex structures. The conventional mushroom structure decays due to the mixing, and the separated rows structure decays because its arrangement is hydrodynamically unstable.

Secondary flow induced by riblets

1998 ◽  
Vol 363 ◽  
pp. 115-151 ◽  
Author(s):  
D. B. GOLDSTEIN ◽  
T.-C. TUAN
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Secondary Flow ◽  
Experimental Studies ◽  
Domain Size ◽  
Secondary Flows ◽  
Matched Pairs ◽  
Two Dimensional ◽  
Streamwise Vortices ◽  
Fully Developed Turbulent Flow

The effects of riblets on one wall of a channel bounding fully developed turbulent flow are investigated. Various perturbation elements including wires, fins and slots are modelled in order to understand the effects of riblets. It is found that widely spaced riblets, fins and wires create a substantial increase in turbulent activity just above the element. These elements are also found to produce a remarkable pattern of secondary mean flows consisting of matched pairs of streamwise vortices. The secondary flows occur only if the bulk flow is turbulent and their characteristics depend on element geometry. It is suggested that these secondary flows are strongly linked with the increase in drag experienced by widely spaced riblets in experimental studies. The secondary flows are probably caused by two-dimensional spanwise sloshing of the flow, inherent in a turbulent boundary layer, interacting with the stream-aligned element. This two-dimensional mechanism is investigated with a series of two-dimensional simulations of sloshing flow over isolated elements. Grid resolution and domain size checks are made throughout the investigation.

Quantitative Study of Excitation of Unsteady Görtler Instability Modes in Concave-Wall Boundary Layer by Free-Stream Turbulence

2014 ◽  
Vol 9 (2) ◽  
pp. 84-94
Author(s):  
Andrey Ivanov ◽  
Yuriy Kachanov ◽  
Dmitriy Mischenko
Keyword(s):  
Boundary Layer ◽  
Physical Phenomenon ◽  
Linear Stability Theory ◽  
Free Stream Turbulence ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Instability Modes ◽  
Concave Wall ◽  
Quantitative Characteristics ◽  
First Time

The paper is devoted to the first experimental study of distributed excitation of Görtler instability modes due the distributed mechanism of receptivity of a concave-wall boundary layer to streamwise freestream vortices. Experiments are carried out in the following range of problem parameters: Görtler numbers G* = 7,4÷21,3, frequencies f = 15, 20, and 26 Hz (nondimensional frequency parameters are F = 17,04; 22,72 and 29,54), and a broad range of spanwise scales of disturbances z = 8÷24 мм (nondimensional scales are Λ = 149÷774). It is found that this receptivity mechanism is quite efficient and can lead to amplification of unsteady Görtler vortices even in regimes where the boundary layer is linearly stable to these boundary-layer disturbances. Estimations of quantitative characteristics of the investigated physical phenomenon: the complex values of the distributed vortex receptivity coefficients are obtained in the present study for the first time. It is found that examined receptivity mechanism is especially effective for vortices with spanwise wavelengths close to the most dangerous in terms of the linear stability theory. The amplitudes of the receptivity coefficients are found to decrease with the streamwise coordinate

The Departure from Equilibrium of Turbulent Boundary Layers

1968 ◽  
Vol 19 (1) ◽  
pp. 1-19 ◽  
Author(s):  
H. McDonald
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Kinetic Energy ◽  
Stress Distribution ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Two Dimensional ◽  
Pressure Distributions ◽  
Momentum Integral ◽  
State Examination

SummaryRecently two authors, Nash and Goldberg, have suggested, intuitively, that the rate at which the shear stress distribution in an incompressible, two-dimensional, turbulent boundary layer would return to its equilibrium value is directly proportional to the extent of the departure from the equilibrium state. Examination of the behaviour of the integral properties of the boundary layer supports this hypothesis. In the present paper a relationship similar to the suggestion of Nash and Goldberg is derived from the local balance of the kinetic energy of the turbulence. Coupling this simple derived relationship to the boundary layer momentum and moment-of-momentum integral equations results in quite accurate predictions of the behaviour of non-equilibrium turbulent boundary layers in arbitrary adverse (given) pressure distributions.

Sign in / Sign up

Export Citation Format

Share Document