scholarly journals Statistical Structure and Deviations from Equilibrium in Wavy Channel Turbulence

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 161 ◽  
Author(s):  
Saadbin Khan ◽  
Balaji Jayaraman
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Outer Layer ◽  
Strong Dependence ◽  
Surface Topology ◽  
Intermittent Flow ◽  
Turbulence Structure ◽  
Near Surface ◽  
Practical Applications ◽  
Major Interest

The structure of turbulent flow over non-flat surfaces is a topic of major interest in practical applications in both engineering and geophysical settings. A lot of work has been done in the fully rough regime at high Reynolds numbers where the effect on the outer layer turbulence structure and the resulting friction drag is well documented. It turns out that surface topology plays a significant role on the flow drag especially in the transitional roughness regime and therefore, is hard to characterize. Survey of literature shows that roughness function depends on the interaction of roughness height, flow Reynolds number, and topology shape. In addition, if the surface topology contains large enough scales then it can impact the outer layer dynamics and in turn modulate the total frictional force. Therefore, it is important to understand the mechanisms underlying drag increase from systematically varied surface undulations in order to better interpret quantifications based on mean statistics such as roughness function. In this study, we explore the mechanisms that modulate the turbulence structure over a two-dimensional (2D) sinusoidal wavy surface with a fixed amplitude, but varying slopes that are sufficiently small to generate only intermittent flow separation. To accomplish this, we perform a set of highly resolved direct numerical simulations (DNS) to model the turbulent flow between two infinitely wide 2D wavy plates at a friction Reynolds number, R e τ = 180 , which represents modest scale separation. We pursue two different but related flavors of analysis. The first one adopts a roughness characterization flavor of such wavy surfaces. The second one focuses on understanding the nonequilibrium near-surface turbulence structure and their impact on roughness characterization. Analysis of the different statistical quantifications show strong dependence on wave slope for the roughness function indicating drag increase due to enhanced turbulent stresses resulting from increased production of vertical velocity variance from the surface undulations.

scholarly journals Statistical Structure and Deviations from Equilibrium in Wavy Channel Turbulence

2019 ◽  
Author(s):  
Saadbin Khan ◽  
Balaji Jayaraman
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Outer Layer ◽  
Strong Dependence ◽  
Surface Topology ◽  
Turbulence Structure ◽  
Near Surface ◽  
Practical Applications ◽  
Flat Surfaces ◽  
Major Interest

The structure of turbulent flow over non-flat surfaces is a topic of major interest in practical applications in both engineering and geophysical settings. A lot of work has been done in the fully rough regime at high Reynolds numbers where the effect on the outer layer turbulence structure and the resulting friction drag is well documented. It turns out that surface topology plays a significant role on the flow drag especially in the transitional roughness regime and therefore, hard to characterize. Survey of literature shows that roughness function depends on the interaction of roughness height, flow Reynolds number and topology shape. In addition, if the surface topology contains large enough scales then it can impact the outer layer dynamics and in turn modulate the total frictional force. Therefore, it is important to understand the mechanisms underlying drag increase from systematically varied surface undulations in order to better interpret quantifications based on mean statistics such as roughness function. In this study, we explore the mechanisms that modulate the turbulence structure over a two-dimensional (2D) sinusoidal wavy surface with a fixed amplitude, but varying slope. To accomplish this, we model the turbulent flow between two infinitely wide 2D wavy plates at a friction Reynolds number, $Re_{\tau}=180$. We pursue two different but related flavors of analysis. The first one adopts a roughness characterization flavor of such wavy surfaces. The second one focuses on understanding the non-equilibrium near surface turbulence structure and their impact on roughness characterization. Analysis of the different statistical quantifications show strong dependence on wave slope for the roughness function indicating drag increase due to enhanced turbulent stresses resulting from increased production of vertical velocity variance from the surface undulations.

scholarly journals Laminarisation of flow at low Reynolds number due to streamwise body force

2016 ◽  
Vol 809 ◽  
pp. 31-71 ◽  
Author(s):  
S. He ◽  
K. He ◽  
M. Seddighi
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Body Force ◽  
Turbulent Viscosity ◽  
The Body ◽  
Wall Turbulence ◽  
Turbulence Structure ◽  
Pressure Force ◽  
Conventional View ◽  
Ejections And Sweeps

It is well established that when a turbulent flow is subjected to a non-uniform body force, the turbulence may be significantly suppressed in comparison with that of the flow of the same flow rate and hence the flow is said to be laminarised. This is the situation in buoyancy-aided mixed convection when severe heat transfer deterioration may occur. Here we report results of direct numerical simulations of flow with a linear or a step-change profile of body force. In contrast to the conventional view, we show that applying a body force to a turbulent flow while keeping the pressure force unchanged causes little changes to the key characteristics of the turbulence. In particular, the mixing characteristics of the turbulence represented by the turbulent viscosity remain largely unaffected. The so-called flow laminarisation due to a body force is in effect a reduction in the apparent Reynolds number of the flow, based on an apparent friction velocity associated with only the pressure force of the flow (i.e. excluding the contribution of the body force). The new understanding allows the level of the flow ‘laminarisation’ and when the full laminarisation occurs to be readily predicted. In terms of the near-wall turbulence structure, the numbers of ejections and sweeps are little influenced by the imposition of the body force, whereas the strength of each event may be enhanced if the coverage of the body force extends significantly away from the wall. The streamwise turbulent stress is usually increased in accordance with the observation of more and stronger elongated streaks, but the wall-normal and the circumferential turbulent stresses are largely unchanged.

Near-Surface Topology of Unmanned Combat Air Vehicle Planform: Reynolds Number Dependence

2005 ◽  
Vol 42 (5) ◽  
pp. 1318-1330 ◽  
Author(s):  
M. Elkhoury ◽  
M. M. Yavuz ◽  
D. Rockwell
Keyword(s):  
Reynolds Number ◽  
Surface Topology ◽  
Near Surface ◽  
Air Vehicle ◽  
Reynolds Number Dependence

Reynolds number effects in the outer layer of the turbulent flow in a channel with rough walls

2005 ◽  
Vol 17 (6) ◽  
pp. 065101 ◽  
Author(s):  
Ole Martin Bakken ◽  
Per-Åge Krogstad ◽  
Alireza Ashrafian ◽  
Helge I. Andersson
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Outer Layer ◽  
Rough Walls ◽  
Reynolds Number Effects

Turbulence Measurements in a Corner Wall Jet1

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Numerical Code ◽  
Wall Jet ◽  
Hot Wire ◽  
Practical Applications ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one-half of the surface has been rotated counterclockwise by 90 deg. The corner wall jet is selected for study as the geometry occurs in practical applications and is an ideal benchmark case for numerical code validation. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry from x/D = 0 to 40. The results indicate that the ratio of lateral-to-vertical growth in the corner wall jet is approximately half that in a standard turbulent three-dimensional wall jet. The results indicate that this behavior is not simply tied to a slower development of the corner wall jet.

Turbulence structure manipulation in a channel flow by outer layer devices

1994 ◽  
Vol 98 (980) ◽  
pp. 388-394 ◽  
Author(s):  
G. Iuso
Keyword(s):  
Reynolds Number ◽  
Spectral Analysis ◽  
Drag Reduction ◽  
Skin Friction ◽  
Channel Flow ◽  
Outer Layer ◽  
Friction Reduction ◽  
Turbulence Structure ◽  
Local Skin ◽  
Integral Scales

Abstract An experimental study has been performed manipulating a fully developed turbulent channel flow, by means of blade manipulators known as outer layer devices (Olds). A large amount of investigation has been performed for boundary layer flow, whereas little research is available for internal flow manipulation. The influence on drag reduction for different configurations (single and tandem) and for some geometric parameters (distance from the wall and blade gap), have been analysed. Reynolds number effect has also been investigated. Some of the mechanisms involved in the skin friction reduction process are examined, in terms of time-space integral scales, Reynolds stresses and spectral analysis. Results show better efficiency for tandem configurations. These give high local skin friction reductions, up to 20%, which are strongly dependent on the manipulator distance from the wall, but have very little dependence on the blade gap and Reynolds number. Turbulence analysis displays reduced fluctuations in all three directions — as with space-time integral scales. Evidence of suppression for the large structures is also shown by spectral analysis. From a global balance it has been verified that no net drag reduction is obtained due to the additional drag introduced by the manipulators.

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

Turbulent flow between concentric rotating cylinders at large Reynolds number

1992 ◽  
Vol 68 (10) ◽  
pp. 1515-1518 ◽  
Author(s):  
Daniel P. Lathrop ◽  
Jay Fineberg ◽  
Harry L. Swinney
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Large Reynolds Number ◽  
Rotating Cylinders

Parameter Extension Simulation of Turbulent Flows in a Compressor Cascade With a High Reynolds Number

2020 ◽  
Author(s):  
Yan Jin
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Simulation Method ◽  
Potential Method ◽  
Navier Stokes ◽  
Reference Solution ◽  
Compressor Cascade ◽  
High Reynolds

Abstract The turbulent flow in a compressor cascade is calculated by using a new simulation method, i.e., parameter extension simulation (PES). It is defined as the calculation of a turbulent flow with the help of a reference solution. A special large-eddy simulation (LES) method is developed to calculate the reference solution for PES. Then, the reference solution is extended to approximate the exact solution for the Navier-Stokes equations. The Richardson extrapolation is used to estimate the model error. The compressor cascade is made of NACA0065-009 airfoils. The Reynolds number 3.82 × 105 and the attack angles −2° to 7° are accounted for in the study. The effects of the end-walls, attack angle, and tripping bands on the flow are analyzed. The PES results are compared with the experimental data as well as the LES results using the Smagorinsky, k-equation and WALE subgrid models. The numerical results show that the PES requires a lower mesh resolution than the other LES methods. The details of the flow field including the laminar-turbulence transition can be directly captured from the PES results without introducing any additional model. These characteristics make the PES a potential method for simulating flows in turbomachinery with high Reynolds numbers.

Sign in / Sign up

Export Citation Format

Share Document