Transition to turbulence in an oscillatory flow over a rough wall

2016 ◽  
Vol 792 ◽  
pp. 67-97 ◽  
Author(s):  
Marco Mazzuoli ◽  
Giovanna Vittori
Keyword(s):  
Reynolds Number ◽  
Incompressible Flow ◽  
Oscillatory Flow ◽  
Unsteady Flows ◽  
Flow Regimes ◽  
Rough Wall ◽  
Transition To Turbulence ◽  
Rigid Spheres

A study of the oscillatory incompressible flow close to a wall covered with fixed rigid spheres is carried out by numerical means to provide information on unsteady flows over a rough wall. The simulations are carried out for two bottom configurations, characterized by different values of the diameter of the spheres and different values of the Reynolds number for a total of 10 cases. Three different flow regimes are identified as functions of both the Reynolds number and the diameter of the spheres. The force exerted by the flow on the spheres is discussed also in relation to the different flow regimes.

scholarly journals Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

Actuators ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 185
Author(s):  
Zuzana Antošová ◽  
Zdeněk Trávníček
Keyword(s):  
Reynolds Number ◽  
Active Control ◽  
Flow Regimes ◽  
Velocity Profiles ◽  
Synthetic Jet ◽  
Transition To Turbulence ◽  
Jet Flows ◽  
Maximal Effect ◽  
Hot Wire ◽  
Round Jet

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

scholarly journals Experimental investigation of transitional flow in a toroidal pipe

2013 ◽  
Vol 738 ◽  
pp. 463-491 ◽  
Author(s):  
J. Kühnen ◽  
M. Holzner ◽  
B. Hof ◽  
H. C. Kuhlmann
Keyword(s):  
Reynolds Number ◽  
Oscillatory Flow ◽  
Flow Instability ◽  
Measurement Techniques ◽  
Stereoscopic Particle Image Velocimetry ◽  
Transition To Turbulence ◽  
Transitional Flow ◽  
Mean Flow ◽  
Steel Sphere ◽  
Curved Pipes

AbstractThe flow instability and further transition to turbulence in a toroidal pipe (torus) with curvature ratio (tube-to-coiling diameter) 0.049 is investigated experimentally. The flow inside the toroidal pipe is driven by a steel sphere fitted to the inner pipe diameter. The sphere is moved with constant azimuthal velocity from outside the torus by a moving magnet. The experiment is designed to investigate curved pipe flow by optical measurement techniques. Using stereoscopic particle image velocimetry, laser Doppler velocimetry and pressure drop measurements, the flow is measured for Reynolds numbers ranging from 1000 to 15 000. Time- and space-resolved velocity fields are obtained and analysed. The steady axisymmetric basic flow is strongly influenced by centrifugal effects. On an increase of the Reynolds number we find a sequence of bifurcations. For $\mathit{Re}= 4075\pm 2\hspace{0.167em} \% $ a supercritical bifurcation to an oscillatory flow is found in which waves travel in the streamwise direction with a phase velocity slightly faster than the mean flow. The oscillatory flow is superseded by a presumably quasi-periodic flow at a further increase of the Reynolds number before turbulence sets in. The results are found to be compatible, in general, with earlier experimental and numerical investigations on transition to turbulence in helical and curved pipes. However, important aspects of the bifurcation scenario differ considerably.

INCOMPRESSIBLE FLOW AT LOW REYNOLDS NUMBER IN A CONICAL ENTRANCE ORIFICE PLATE

2019 ◽  
Author(s):  
MARA NILZA ESTANISLAU REIS ◽  
Wender Oliveira ◽  
Pedro Américo Almeida Magalhães Júnior
Keyword(s):  
Reynolds Number ◽  
Incompressible Flow ◽  
Low Reynolds Number ◽  
Orifice Plate ◽  
Low Reynolds

POSITIVITY OF k-EPSILON TURBULENCE MODELS FOR INCOMPRESSIBLE FLOW

2002 ◽  
Vol 12 (03) ◽  
pp. 393-406 ◽  
Author(s):  
ZI-NIU WU ◽  
SONG FU
Keyword(s):  
Reynolds Number ◽  
Point Source ◽  
Incompressible Flow ◽  
Iterative Procedure ◽  
High Reynolds Number ◽  
Operator Splitting ◽  
Turbulence Models ◽  
Diffusion Equations ◽  
Advection Diffusion ◽  
High Reynolds

The k-epsilon turbulence model for incompressible flow involves two advection–diffusion equations plus point-source terms. We propose a new method for positivity analysis. This method uses an iterative procedure combined with an operator splitting. With this method we recover the well-known positivity result for the standard high Reynolds number model. Most importantly, we are able to prove the positivity result for general low Reynolds number k-epsilon models.

Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows

1995 ◽  
Vol 48 (4) ◽  
pp. 189-212 ◽  
Author(s):  
G. J. Brereton ◽  
R. R. Mankbadi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Unsteady Flows ◽  
Turbulence Models ◽  
Research Area ◽  
Transition To Turbulence ◽  
Measurement Technology ◽  
Internal Flows ◽  
Recent Advances ◽  
The Many

Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.

The development of asymmetry and period doubling for oscillatory flow in baffled channels

1996 ◽  
Vol 328 ◽  
pp. 19-48 ◽  
Author(s):  
E. P. L. Roberts ◽  
M. R. Mackley
Keyword(s):  
Reynolds Number ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Period Doubling ◽  
Progressive Increase ◽  
Newtonian Flow ◽  
Chaotic Flow ◽  
Spatially Periodic ◽  
Dimensional Simulation ◽  
Time Periodic

We report experimental and numerical observations on the way initially symmetric and time-periodic fluid oscillations in baffled channels develop in complexity. Experiments are carried out in a spatially periodic baffled channel with a sinusoidal oscillatory flow. At modest Reynolds number the observed vortex structure is symmetric and time periodic. At higher values the flow progressively becomes three-dimensional, asymmetric and aperiodic. A two-dimensional simulation of incompressible Newtonian flow is able to follow the flow pattern at modest oscillatory Reynolds number. At higher values we report the development of both asymmetry and a period-doubling cascade leading to a chaotic flow regime. A bifurcation diagram is constructed that can describe the progressive increase in complexity of the flow.

scholarly journals Convective cooling of tandem heated triangular cylinders placed in a channel

2010 ◽  
Vol 14 (1) ◽  
pp. 183-197 ◽  
Author(s):  
Afshin Mohsenzadeh ◽  
Mousa Farhadi ◽  
Kurosh Sedighi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Simulations ◽  
Incompressible Flow ◽  
Horizontal Plane ◽  
Plane Channel ◽  
Reynolds Numbers ◽  
Convective Cooling ◽  
Wall Proximity ◽  
Fluid Characteristics

Numerical simulations of forced convective incompressible flow in a horizontal plane channel with adiabatic walls over two isothermal tandem triangular cylinders of equal size are presented to investigate the effect of wall proximity of obstacles, gap space (i.e. gap between two squares), and Reynolds number. Computations have been carried out for Reynolds numbers of (based on triangle width) 100, 250, and 350. Results show that, wall proximity has different effect on first and second triangle in fluid characteristics especially in lower gap spaced, while for heat transfer a fairly same behavior was seen.

Oscillatory flow regimes around four cylinders in a diamond arrangement

2019 ◽  
Vol 877 ◽  
pp. 955-1006 ◽  
Author(s):  
Chengjiao Ren ◽  
Liang Cheng ◽  
Feifei Tong ◽  
Chengwang Xiong ◽  
Tingguo Chen
Keyword(s):  
Oscillatory Flow ◽  
Bluff Body ◽  
Substantial Reduction ◽  
Period Doubling ◽  
Flow Regimes ◽  
Mode Competition ◽  
Single Type ◽  
Phase Dynamics ◽  
Flow Features ◽  
Four Cylinders

Oscillatory flow around a cluster of four circular cylinders in a diamond arrangement is investigated using two-dimensional direct numerical simulation over Keulegan–Carpenter numbers (KC) ranging from 4 to 12 and Reynolds numbers (Re) from 40 to 230 at four gap-to-diameter ratios (G) of 0.5, 1, 2 and 4. Three types of flows, namely synchronous, quasi-periodic and desynchronized flows (along with 14 flow regimes) are mapped out in the (G, KC, Re)-parameter space. The observed flow characteristics around four cylinders in a diamond arrangement show a few unique features that are absent in the flow around four cylinders in a square arrangement reported by Tong et al. (J. Fluid Mech., vol. 769, 2015, pp. 298–336). These include (i) the dominance of flow around the cluster-scale structure at $G=0.5$ and 1, (ii) a substantial reduction of regime D flows in the regime maps, (iii) new quasi-periodic (phase trapping) $\text{D}^{\prime }$ (at $G=0.5$ and 1) and period-doubling $\text{A}^{\prime }$ flows (at $G=1$) and most noteworthily (iv) abnormal behaviours at ($G\leqslant 2$) (referred to as holes hereafter) such as the appearance of spatio-temporal synchronized flows in an area surrounded by a single type of synchronized flow in the regime map ($G=0.5$). The mode competition between the cluster-scale and cylinder-scale flows is identified as the key flow mechanism responsible for those unique flow features, with the support of evidence derived from quantitative analysis. Phase dynamics is introduced for the first time in bluff-body flows, to the best knowledge of the authors, to quantitatively interpret the flow response (e.g. quasi-periodic flow features) around the cluster. It is instrumental in revealing the nature of regime $\text{D}^{\prime }$ flows where the cluster-scale flow features are largely synchronized with the forcing of incoming oscillatory flow (phase trapping) but are modulated by localized flow features.

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