scholarly journals Networked configurations as an emergent property of transverse aeolian ridges on Mars

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
T. P. Nagle-McNaughton ◽  
L. A. Scuderi
Keyword(s):  
Three Dimensional ◽  
Spatial Density ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Martian Surface ◽  
Three Dimensional Flow ◽  
Linear Forms ◽  
Dimensional Flow ◽  
Roughness Elements ◽  
Two Dimensional Flow

AbstractTransverse aeolian ridges – enigmatic Martian features without a proven terrestrial analog – are increasingly important to our understanding of Martian surface processes. However, it is not well understood how the relationships between different ridges evolve. Here we present a hypothesis for the development of complex hexagonal networks from simple linear forms by analyzing HiRISE images from the Mars Reconnaissance Orbiter. We identify variable morphologies which show the presence of secondary ridges, feathered transverse aeolian ridges and both rectangular and hexagonal networks. We propose that the formation of secondary ridges and the reactivation of primary ridge crests produces sinuous networks which then progress from rectangular cells towards eventual hexagonal cells. This morphological progression may be explained by the ridges acting as roughness elements due to their increased spatial density which would drive a transition from two-dimensional bedforms under three-dimensional flow conditions, to three-dimensional bedforms under two-dimensional flow conditions.

Three-dimensional flow in cavities

1963 ◽  
Vol 16 (4) ◽  
pp. 620-632 ◽  
Author(s):  
D. J. Maull ◽  
L. F. East
Keyword(s):  
Static Pressure ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Large Span ◽  
Dimensional Flow ◽  
Pressure Distributions ◽  
Oil Flow ◽  
Two Dimensional Flow

The flow inside rectangular and other cavities in a wall has been investigated at low subsonic velocities using oil flow and surface static-pressure distributions. Evidence has been found of regular three-dimensional flows in cavities with large span-to-chord ratios which would normally be considered to have two-dimensional flow near their centre-lines. The dependence of the steadiness of the flow upon the cavity's span as well as its chord and depth has also been observed.

Cellular flow in a partially filled rotating drum: regular and chaotic advection

2017 ◽  
Vol 825 ◽  
pp. 631-650 ◽  
Author(s):  
Francesco Romanò ◽  
Arash Hajisharifi ◽  
Hendrik C. Kuhlmann
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Chaotic Advection ◽  
Two Dimensional ◽  
Rotating Drum ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Heteroclinic Connection ◽  
Two Dimensional Flow ◽  
Chaotic Streamlines

The topology of the incompressible steady three-dimensional flow in a partially filled cylindrical rotating drum, infinitely extended along its axis, is investigated numerically for a ratio of pool depth to radius of 0.2. In the limit of vanishing Froude and capillary numbers, the liquid–gas interface remains flat and the two-dimensional flow becomes unstable to steady three-dimensional convection cells. The Lagrangian transport in the cellular flow is organised by periodic spiralling-in and spiralling-out saddle foci, and by saddle limit cycles. Chaotic advection is caused by a breakup of a degenerate heteroclinic connection between the two saddle foci when the flow becomes three-dimensional. On increasing the Reynolds number, chaotic streamlines invade the cells from the cell boundary and from the interior along the broken heteroclinic connection. This trend is made evident by computing the Kolmogorov–Arnold–Moser tori for five supercritical Reynolds numbers.

Theoretical Aspects of Thrust Vector Control by Secondary Gas Injection in Rocket Nozzles

1968 ◽  
Vol 72 (686) ◽  
pp. 171-177 ◽  
Author(s):  
John H. Neilson ◽  
Alastair Gilchrist ◽  
Chee K. Lee
Keyword(s):  
Vector Control ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Side Force ◽  
Thrust Vector Control ◽  
Dimensional Flow ◽  
Two Dimensional Flow ◽  
Thrust Vector ◽  
Secondary Injection

This work deals with theoretical aspects of thrust vector control in rocket nozzles by the injection of secondary gas into the supersonic region of the nozzle. The work is concerned mainly with two-dimensional flow, though some aspects of three-dimensional flow in axisymmetric nozzles are considered. The subject matter is divided into three parts. In Part I, the side force produced when a physical wedge is placed into the exit of a two-dimensional nozzle is considered. In Parts 2 and 3, the physical wedge is replaced by a wedge-shaped “dead water” region produced by the separation of the boundary layer upstream of a secondary injection port. The modifications which then have to be made to the theoretical relationships, given in Part 1, are enumerated. Theoretical relationships for side force, thrust augmentation and magnification parameter for two- and three-dimensional flow are given for secondary injection normal to the main nozzle axis. In addition, the advantages to be gained by secondary injection in an upstream direction are clearly illustrated. The theoretical results are compared with experimental work and a comparison is made with the theories of other workers.

A Theory for the Side Force produced in Two-Dimensional Nozzles by Secondary Gas Injection

1968 ◽  
Vol 72 (687) ◽  
pp. 267-274
Author(s):  
John H. Neilson ◽  
Alastair Gilchrist ◽  
Chee K. Lee
Keyword(s):  
Gas Injection ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Side Force ◽  
Dimensional Flow ◽  
Increase With Increase ◽  
Two Dimensional Flow ◽  
Secondary Port ◽  
Theoretical Side

Summary:This work is concerned with the side force produced in rocket nozzles by secondary gas injection. A new theory for determining the side force is presented for two-dimensional flow and this is considered to be an important step towards a theory applicable to three-dimensional flow. The proposed theory is based on a double wedge model for the separated region upstream of the secondary port. The principal feature of the model is that it accounts tor the fact that the angle of the shock wave, originating from the separated region, is observed to increase with increase in secondary mass flow rate. Theoretical side force results are shown to compare favourably with experimental results obtained using two-dimensional nozzles and a comparison is made between the proposed theory and the theories of other workers.

A Comparison of Forces in Two- and Three-Dimensional Flow Past an Oscillating Cylinder

2015 ◽  
Author(s):  
Sofia Peppa ◽  
Lambros Kaiktsis ◽  
Christos Frouzakis ◽  
George Triantafyllou
Keyword(s):  
Stokes Equations ◽  
Oscillation Amplitude ◽  
Three Dimensional ◽  
Oscillation Mode ◽  
Transverse Oscillation ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Past ◽  
Two Dimensional Flow

DNS results are presented for three-dimensional flow past a circular cylinder forced to oscillate both in the transverse and in-line direction with respect to a uniform stream, at Reynolds number equal to 400, and are compared against simulation results for two-dimensional flow. The cylinder follows a figure-eight motion, traversed either counter-clockwise or clockwise in the upper half-plane for a flow stream from left to right. The transverse oscillation frequency is equal to the natural frequency of the Kármán vortex street. The Navier-Stokes equations are solved using a spectral element code, and the forces acting on the cylinder are computed for both three- and two-dimensional flow. The results demonstrate that the effect of cylinder oscillation on the flow structure and forces differs substantially between the counter-clockwise and the clockwise oscillation mode. For the counter-clockwise mode, forcing at low amplitude decreases the flow three-dimensionality, with the wake becoming increasingly three-dimensional for transverse oscillation amplitudes higher than 0.25–0.30 cylinder diameters, with corresponding discrepancies in forces with respect to two-dimensional flow. For the case of clockwise mode, a strong stabilizing effect is found: the wake becomes two-dimensional for a transverse oscillation amplitude of 0.20 cylinder diameters, and remains so at higher amplitudes, resulting in nearly equal values of the force coefficients for three- and two-dimensional flow.

Perspective: Selected Benchmarks From Commercial CFD Codes

1995 ◽  
Vol 117 (2) ◽  
pp. 208-218 ◽  
Author(s):  
C. J. Freitas
Keyword(s):  
Three Dimensional ◽  
Separated Flow ◽  
Policy Statement ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Common Reference ◽  
Reynolds Number Flow ◽  
Flow Problems ◽  
Dimensional Flow ◽  
Two Dimensional Flow

This paper summarizes the results of a series of five benchmark simulations which were completed using commercial Computational Fluid Dynamics (CFD) codes. These simulations were performed by the vendors themselves, and then reported by them in ASME’s CFD Triathlon Forum and CFD Biathlon Forum. The first group of benchmarks consisted of three laminar flow problems. These were the steady, two-dimensional flow over a backward-facing step, the low Reynolds number flow around a circular cylinder, and the unsteady three-dimensional flow in a shear-driven cubical cavity. The second group of benchmarks consisted of two turbulent flow problems. These were the two-dimensional flow around a square cylinder with periodic separated flow phenomena, and the steady, three-dimensional flow in a 180-degree square bend. All simulation results were evaluated against existing experimental data and thereby satisfied item 10 of the Journal’s policy statement for numerical accuracy. The objective of this exercise was to provide the engineering and scientific community with a common reference point for the evaluation of commercial CFD codes.

Three Dimensional Flow Around a Biomimetic Unbounded Flapping Cantilever

2013 ◽  
Author(s):  
Andrew Eastman ◽  
Mark Kimber
Keyword(s):  
Thermal Management ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Numerical Studies ◽  
Image Velocimetry ◽  
Two Dimensional Flow ◽  
Simple Extrapolation ◽  
Insight Into

Macro-sized cantilevers oscillating in a fluid have been employed in applications ranging from thermal management to propulsion and represent a realistic tradeoff between full biomimicry and ease of fabrication. Surprisingly, the flow field generated upstream and downstream of the cantilever remains poorly understood. In order to properly control the resulting flow, further experimental and numerical studies are needed. From a two dimensional perspective, comprehensive analysis has been done, primarily through employing a single, very wide cantilever. However, many applications necessitate the usage of oscillating cantilevers whose oscillating amplitude is comparable to their width. As the region of analysis moves closer to a corner, where two edges of the slender cantilever meet, the flow becomes extremely three dimensional, rendering the two dimensional analysis tools less useful. The following paper seeks to further understand the highly three dimensional nature of the flow in addition to providing further insight into optimized flow control. Two perpendicular flow planes are analyzed in order to gather the x, y and z directional flow velocities using standard Particle Image Velocimetry measurements. It is shown that under certain circumstances, the resulting flow is atypical of what one would expect from a simple extrapolation from previous two dimensional flow analyses.

Note on the interpretation of two-dimensional theories of growing cavities

1964 ◽  
Vol 19 (1) ◽  
pp. 137-144 ◽  
Author(s):  
T. Brooke Benjamin
Keyword(s):  
Logarithmic Singularity ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Plane Flow ◽  
Dimensional Flow ◽  
Physical Approximation ◽  
Two Dimensional Flow ◽  
Inner Region ◽  
Main Ideas

It is shown in general how a two-dimensional flow can be justified as a physical approximation, notwithstanding the logarithmic singularity in pressure that occurs at infinity when the cavity expands or contracts at a varying rate. The argument presented, which affords a more natural interpretation than alternatives previously suggested, refers to the approximate equivalence-to a determinable degree of accuracy-between the hypothetical plane flow and the inner region of some real three-dimensional flow with small spanwise variations. The main ideas are illustrated by the example of a long ellipsoidal body which changes in volume while also undergoing shape perturbations.

Note on Transition to Turbulence in Vortex-Street Wakes

1967 ◽  
Vol 71 (684) ◽  
pp. 866-867 ◽  
Author(s):  
M. M. Zdravkovich
Keyword(s):  
Essential Feature ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Transition To Turbulence ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Vortex Filaments ◽  
Dimensional Flow ◽  
Vortex Loops ◽  
Two Dimensional Flow

In their pioneering paper published in 1917 Nayler and Frazer showed that the process of vortex formation behind a circular cylinder can have significant three-dimensional features even when care is taken to create two-dimensional flow. Hama produced photographs which show initially straight vortex filaments becoming curved some distance behind the cylinder, with consequent three-dimensional flow. In their experiments on boundary layers Hama et al found the formation and development of “vortex loops” from such curved vortex filaments to be an essential feature preceding transition from laminar to turbulent flow, and they stated that the same would be true for transition in wakes and jets.

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