The motion of two-dimensional vortex pairs in a ground effect

1977 ◽  
Vol 82 (4) ◽  
pp. 659-671 ◽  
Author(s):  
Steven J. Barker ◽  
Steven C. Crow
Keyword(s):  
High Speed ◽  
Ground Plane ◽  
Vortex Formation ◽  
Ground Effect ◽  
Transition To Turbulence ◽  
High Speed Photography ◽  
Surface Boundary ◽  
Water Tank ◽  
Two Dimensional ◽  
Mean Flow

A new technique for generating a pair of line vortices in the laboratory has been developed. The mean flow of these vortices is highly two-dimensional, although most of the flow field is turbulent. This two-dimensionality permits the study of vortex motions in the absence of the Crow mutual induction instability and other three-dimensional effects. The vortices are generated in a water tank of dimensions 15 × 122 × 244 cm. They propagate vertically and their axes span the 15 cm width of the tank. One wall of the tank is transparent, and the flow is visualized using fluorescein dye. High speed photography is used to study both the transition to turbulence during the vortex formation process and the interaction of the turbulent vortices with a simulated ground plane.Transition occurs first in an annular region surrounding the core of each vortex, starting with a shear-layer instability on the rolled-up vortex sheet. The turbulent region then grows both radially inwards and radially outwards until the entire recirculation cell is turbulent. A ‘relaminarization’ of the vortex core appears to take place somewhat later.The interaction of the vortex pair with the ground plane does not follow the predictions of potential-flow theory for line vortices. Although the total circulation is apparently conserved, the vortices remain at a larger distance from the ground than is expected and eventually ‘rebound’ or move away from the ground. Differences between a free-surface boundary condition and a smooth or rough ground plane are discussed. The ground-plane interaction is qualitatively very similar to that of aircraft trailing vortices observed in recent flight tests.

Study of Scale-Interactions in Strained and Destrained Turbulence

2004 ◽  
Author(s):  
Jun Chen ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
High Speed ◽  
High Speed Photography ◽  
Water Tank ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Scale Interactions ◽  
Background Turbulence ◽  
High Reynolds

This paper examines the interactions among different length-scales of turbulence during straining and de-straining of the flow. Understanding scale-interactions is a crucial ingredient in formulating improved subgrid models for Large Eddy Simulations. In this experimental study, planar Particle Image Velocimetry (PIV) measurements are performed in a water tank, in which high Reynolds number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining are applied by pushing or pulling rectangular piston whose width is equal to that of the a rectangular tank towards and away from the bottom. The velocity of the piston is computer controlled and synchronized with the PIV system. The initial background turbulence, characterized by the distributions of rms values and energy spectra, confirms that that the turbulence is nearly isotropic and homogeneous. The applied straining is characterized using high-speed photography of the piston and by PIV measurements of the mean flow. The results consist of the time evolution of several turbulence parameters subjected to a sequence of straining and destraining motions, with particular emphasis on the Reynolds stresses, Sub-grid scale (SGS) stresses, SGS anisotropy and SGS dissipation. The paper also examines the scale dependence of the SGS stress and dissipation, and compares the energy flux between different scales during the straining and destraining parts of the deformation.

scholarly journals Model Experimental Study of Damage Effects of Ship Structures under the Contact Jet Loads of Bubble in a Water Tank

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Hailong Chen ◽  
Baoyu Ni ◽  
Wenjin Hu ◽  
Yanzhuo Xue
Keyword(s):  
High Speed ◽  
Oscillation Amplitude ◽  
Bending Moment ◽  
Oscillation Period ◽  
High Speed Photography ◽  
Beam Model ◽  
Water Tank ◽  
Bending Rigidity ◽  
Ship Structures ◽  
Negative Bending

The damage effects of ship structures under the contact jet loads of bubble are studied by using an electric spark bubble as well as high-speed photography. A series of model experiments of ship structures under contact explosion was carried out in a water tank. On the one hand, we monitored the displacement and period of the oscillation of a hull plate of a ship model with a large bending rigidity. On the other hand, we observed the overall motion of a box-beam model with a small bending rigidity. The results show that when the distance parameter is less than 0.6, the bubble jet will impact on the surface of the structure directly, which is defined as “contact bubble jet” herein. The contact bubble jet causes significant local loads on the ship and induces the “sagging moment” effect. This mainly results from the relatively negative bending moment caused by the bubble attached to the hull. With the increase of detonation distance, this negative bending moment decreases. As a result, the oscillation amplitude of the ship structure decreases sharply and the oscillation period reduces gradually.

Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems

1985 ◽  
Vol 401 (1821) ◽  
pp. 225-249 ◽  
Keyword(s):  
High Speed ◽  
Liquid Drop ◽  
Time History ◽  
Drop Impact ◽  
High Speed Photography ◽  
Two Dimensional ◽  
Surface Geometry ◽  
Repeated Impact ◽  
Liquid Impact ◽  
The Impact

In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser ( Proc . R . Soc . Lond . 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ 0 CU i and at the time of shock-detachment approach ca . 3ρ 0 CU i . At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.

Experimental Investigation on Flow and Breakup of Two-Dimensional Liquid Jets

2019 ◽  
Author(s):  
Amin Jaberi ◽  
Mehran Tadjfar
Keyword(s):  
High Speed ◽  
Volume Flow Rate ◽  
Quantitative Description ◽  
Sheet Thickness ◽  
Liquid Jets ◽  
Liquid Jet ◽  
High Speed Photography ◽  
Two Dimensional ◽  
Aspect Ratios ◽  
Wide Range

Abstract Studying of injectors with non-circular geometries has recently come to the spotlight of researchers as a potential technique to improve the liquid injection characteristics of different systems. In this work, the flow physics and breakup of two-dimensional liquid jets issued from flat slits into still air were experimentally investigated. Three injectors with aspect ratios of 30, 60 and 90 and thickness of 0.35 mm were manufactured to obtain two-dimensional liquid flow at the nozzle exit. The tests were performed for a wide range of volume flow rate, varying from 10 L/h to 240 L/h. Backlight shadowgraphy and high speed photography were employed to capture the flow dynamics of the jets. In order to capture every detail of the flow, photos of the liquid jet were taken from two views with 90° from each other. Using the visualizations, different regimes of the jet flow were explored and a regime map was proposed to distinguish these regimes based on the non-dimensional parameters of the liquid jet. Moreover, quantitative description of the main features of jet flows were obtained using an in-house image processing program. Measurements of different parameters including convergence length, maximum width, breakup length, sheet thickness to name a few, were conducted.

Large-scale vortex structures in turbulent wakes behind bluff bodies. Part 1. Vortex formation processes

1987 ◽  
Vol 174 ◽  
pp. 233-270 ◽  
Author(s):  
A. E. Perry ◽  
T. R. Steiner
Keyword(s):  
Large Scale ◽  
Vector Fields ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Point Theory ◽  
Shear Stresses ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Mean Flow ◽  
Turbulent Wakes

An investigation of turbulent wakes was conducted and phase-averaged velocity vector fields are presented, as well as phase-averaged and global Reynolds normal and shear stresses. The topology of the phase-averaged velocity fields is discussed in terms of critical point theory. Here in Part 1, the vortex formation process in the cavity region of several nominally two-dimensional bluff bodies is investigated and described using phase-averaged streamlines where the measurements were made in a nominal plane of symmetry. It was found that the flows encountered were always three-dimensional and that the mean-flow patterns in the cavity region were quite different from those expected using classical two-dimensional assumptions.

scholarly journals Mean flow characteristics of two-dimensional wings in ground effect

2012 ◽  
Vol 4 (2) ◽  
pp. 151-161 ◽  
Author(s):  
Jae-Hwan Jung ◽  
Hyun-Sik Yoon ◽  
Ho-Hwan Chun ◽  
Pham Anh Hung ◽  
Osama Ahmed Elsamni
Keyword(s):  
Flow Characteristics ◽  
Ground Effect ◽  
Two Dimensional ◽  
Mean Flow

scholarly journals On the Dynamics of Two-Dimensional Hurricane-like Concentric Rings Vortex Formation

2010 ◽  
Vol 67 (10) ◽  
pp. 3253-3268 ◽  
Author(s):  
Y. Martinez ◽  
G. Brunet ◽  
M. K. Yau
Keyword(s):  
Critical Radius ◽  
Vortex Formation ◽  
Interaction Mechanism ◽  
Two Dimensional ◽  
Mean Flow ◽  
Hurricane Intensity ◽  
Wind Maximum ◽  
Vortex Rossby Wave ◽  
Spiral Rainbands ◽  
Strong Vortex

Abstract Despite the fact that asymmetries in hurricanes (e.g., spiral rainbands, polygonal eyewalls, and mesovortices) have long been observed in radar and satellite imagery, many aspects of their dynamics remain unsolved, particularly in the formation of the secondary eyewall. The underlying associated dynamical processes need to be better understood to advance the science of hurricane intensity forecasting. To fill this gap, a simple 2D barotropic “dry” model is used to simulate a hurricane-like concentric rings vortex. The empirical normal mode (ENM) technique, together with Eliassen–Palm (EP) flux calculations, are used to isolate wave modes from the model datasets to investigate their impact on the changes in the structure and intensity of the simulated hurricane-like vortex. From the ENM diagnostics, it is shown that asymmetric disturbances outside a strong vortex ring with a large vorticity skirt may relax to form concentric rings of enhanced vorticity that contain a secondary wind maximum. The fact that the critical radius for some of the leading modes is close to the location where the secondary ring of enhanced vorticity develops suggests that a wave–mean flow interaction mechanism based on vortex Rossby wave (VRW) dynamics may explain important dynamical aspects of concentric eyewall genesis (CEG).

An Experimental Investigation of Rotor–Box Aerodynamic Interaction1

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Dhwanil Shukla ◽  
Narayanan Komerath
Keyword(s):  
High Speed ◽  
Ground Effect ◽  
Tip Vortex ◽  
Mean Flow ◽  
Vehicle Performance ◽  
Package Delivery ◽  
Performance Trends ◽  
Torque Measurements ◽  
Flow Phenomena ◽  
High Level

Abstract Multirotor unmanned aerial vehicles (UAVs) are a promising means of package delivery. Such applications generally involve carrying bulky payloads under the vehicle. Understanding the aerodynamic interaction effects of payloads on the vehicle is the key to design such systems, in the low Reynolds number regime of small UAVs. High-speed particle image velocimetry (PIV), force, and torque measurements have been used with a rotor and a cubic box to investigate the rotor–box interactions and configurations typical of multirotor UAVs. The observed rotor and vehicle performance trends are explained by the mean flow field captured through PIV. Conditions similar to ground-effect operation are developed for the rotor at a high level of rotor-box overlap. A slight improvement in the vehicle performance is observed at conditions where the box is just out of the rotor wake. Some basic instantaneous flow phenomena due to rotor–box interaction have been identified. The interactions have been classified into three distinct modes based on observations at a range of box positions relative to the rotor. An empirical tip vortex trajectory model for isolated rotors is found to be instrumental in predicting the interaction mode at a given box position.

scholarly journals Mean flow characteristics of two-dimensional wings in ground effect

2012 ◽  
Vol 4 (2) ◽  
pp. 151-161 ◽  
Author(s):  
Jae Hwan Jung ◽  
Hyun Sik Yoon ◽  
Ho Hwan Chun ◽  
Pham Anh Hung ◽  
Osama Ahmed Elsamni
Keyword(s):  
Flow Characteristics ◽  
Ground Effect ◽  
Two Dimensional ◽  
Mean Flow

Effect of Nozzle Shape and Polymer Additives on Water Jet Appearance

1979 ◽  
Vol 101 (3) ◽  
pp. 304-308 ◽  
Author(s):  
J. W. Hoyt ◽  
J. J. Taylor
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Water Jet ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Polymer Additives ◽  
High Speed Photography ◽  
Layer Transition ◽  
Spray Formation ◽  
Exit Surface

The effects of shape parameters on the performance of water-jet nozzles discharging in air were investigated using a camera specially adapted for jet photography. The boundary-layer developing on the exit surface of the nozzle is shown to account for the jet appearance revealed by high speed photography. Optimum nozzles seem to have the boundary-layer transition to turbulence inside the nozzle; transition outside the nozzle being accompanied by spray formation and early jet disruption. The effect of polymer additives seems to be earlier transition and a thinner turbulent boundary layer inside the nozzle which improves jet performance.

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