scholarly journals A comparative study of the velocity and vorticity structure in pipes and boundary layers at friction Reynolds numbers up to

2019 ◽  
Vol 869 ◽  
pp. 182-213 ◽  
Author(s):  
S. Zimmerman ◽  
J. Philip ◽  
J. Monty ◽  
A. Talamelli ◽  
I. Marusic ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Structural Difference ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Outer Edge ◽  
Boundary Layer Flows ◽  
Outer Flow ◽  
Wall Flows ◽  
Turbulent Wall

This study presents findings from a first-of-its-kind measurement campaign that includes simultaneous measurements of the full velocity and vorticity vectors in both pipe and boundary layer flows under matched spatial resolution and Reynolds number conditions. Comparison of canonical turbulent flows offers insight into the role(s) played by features that are unique to one or the other. Pipe and zero pressure gradient boundary layer flows are often compared with the goal of elucidating the roles of geometry and a free boundary condition on turbulent wall flows. Prior experimental efforts towards this end have focused primarily on the streamwise component of velocity, while direct numerical simulations are at relatively low Reynolds numbers. In contrast, this study presents experimental measurements of all three components of both velocity and vorticity for friction Reynolds numbers$Re_{\unicode[STIX]{x1D70F}}$ranging from 5000 to 10 000. Differences in the two transverse Reynolds normal stresses are shown to exist throughout the log layer and wake layer at Reynolds numbers that exceed those of existing numerical data sets. The turbulence enstrophy profiles are also shown to exhibit differences spanning from the outer edge of the log layer to the outer flow boundary. Skewness and kurtosis profiles of the velocity and vorticity components imply the existence of a ‘quiescent core’ in pipe flow, as described by Kwonet al. (J. Fluid Mech., vol. 751, 2014, pp. 228–254) for channel flow at lower$Re_{\unicode[STIX]{x1D70F}}$, and characterize the extent of its influence in the pipe. Observed differences between statistical profiles of velocity and vorticity are then discussed in the context of a structural difference between free-stream intermittency in the boundary layer and ‘quiescent core’ intermittency in the pipe that is detectable to wall distances as small as 5 % of the layer thickness.

Self-similar mean dynamics in turbulent wall flows

2013 ◽  
Vol 718 ◽  
pp. 596-621 ◽  
Author(s):  
J. C. Klewicki
Keyword(s):  
Boundary Layer ◽  
Similarity Solution ◽  
Reynolds Numbers ◽  
Channel Height ◽  
Self Similarity ◽  
Mean Velocity ◽  
Wall Flows ◽  
Self Similar ◽  
The Mean ◽  
Turbulent Wall

AbstractThis study investigates how and why dynamical self-similarities emerge with increasing Reynolds number within the canonical wall flows beyond the transitional regime. An overarching aim is to advance a mechanistically coherent description of turbulent wall-flow dynamics that is mathematically tractable and grounded in the mean dynamical equations. As revealed by the analysis of Fife, Klewicki & Wei (J. Discrete Continuous Dyn. Syst.A, vol. 24, 2009, pp. 781–807), the equations that respectively describe the mean dynamics of turbulent channel, pipe and boundary layer flows formally admit invariant forms. These expose an underlying self-similar structure. In all cases, two kinds of dynamical self-similarity are shown to exist on an internal domain that, for all Reynolds numbers, extends from$O(\nu / {u}_{\tau } )$to$O(\delta )$, where$\nu $is the kinematic viscosity,${u}_{\tau } $is the friction velocity and$\delta $is the half-channel height, pipe radius, or boundary layer thickness. The simpler of the two self-similarities is operative on a large outer portion of the relevant domain. This self-similarity leads to an explicit analytical closure of the mean momentum equation. This self-similarity also underlies the emergence of a logarithmic mean velocity profile. A more complicated kind a self-similarity emerges asymptotically over a smaller domain closer to the wall. The simpler self-similarity allows the mean dynamical equation to be written as a closed system of nonlinear ordinary differential equations that, like the similarity solution for the laminar flat-plate boundary layer, can be numerically integrated. The resulting similarity solutions are demonstrated to exhibit nearly exact agreement with direct numerical simulations over the solution domain specified by the theory. At the Reynolds numbers investigated, the outer similarity solution is shown to be operative over a domain that encompasses${\sim }40\hspace{0.167em} \% $of the overall width of the flow. Other properties predicted by the theory are also shown to be well supported by existing data.

Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures

2010 ◽  
Author(s):  
Christian Eichler ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Wall Friction ◽  
Evaluation Procedure ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Flame Flashback ◽  
Turbulent Wall

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.

Wall Heat Flux Under Persistent Vortices

2002 ◽  
Author(s):  
R. E. Breidenthal
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Laminar Flows ◽  
Wall Heat Flux ◽  
Recent Theory ◽  
Turbulent Wall

It is commonly perceived that turbulent flows yield turbulent wall fluxes, while laminar flows yield correspondingly laminar wall fluxes. Experiments support a recent theory that turbulent flows can yield laminar wall fluxes if the flow is “persistent.” Adding strong, stationary vortices to a turbulent boundary layer lowers the wall heat flux to a laminar value.

Numerical Simulation of Turbulent Flows in Ribbed Pipes

2005 ◽  
Author(s):  
Sowjanya Vijiapurapu ◽  
Jie Cui
Keyword(s):  
Turbulent Flows ◽  
Turbulence Models ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Friction Resistance ◽  
Circular Pipes ◽  
Computational Fluid Dynamics Cfd ◽  
Stress Models ◽  
Type Intermediate

The Reynolds averaged Navier-Stokes (RANS) equations were solved along with three turbulence models, namely κ-ε, κ-ω, and Reynolds stress models (RSM), to study the fully developed turbulent flows in circular pipes roughened by repeated square ribs. The spacing between the ribs was varied to form three representative types of surface roughness; d–type, intermediate, and k–type. Solutions of these flows at two Reynolds numbers were obtained using the commercial computational fluid dynamics (CFD) software Fluent. The numerical results were validated against experimental measurements and other numerical data published in literature. Extensive investigation of effects of rib spacing and Reynolds number on the pressure and friction resistance, flow and turbulence distribution was presented. The performance of three turbulence models was also compared and discussed.

Low-Reynolds-Number Turbulent Boundary Layers

1981 ◽  
Vol 103 (4) ◽  
pp. 624-630 ◽  
Author(s):  
B. R. White
Keyword(s):  
Boundary Layer ◽  
Shape Factor ◽  
Reynolds Numbers ◽  
Viscous Sublayer ◽  
Factor H ◽  
Boundary Layer Flows ◽  
Viscous Effects ◽  
Boundary Layer Height ◽  
Wind Tunnel Data ◽  
Logarithmic Velocity Profile

This paper presents experimental wind-tunnel data that show the universal logarithmic velocity profile for zero-pressure-gradient turbulent boundary layer flows is valid for values of momentum-deficit Reynolds numbers Rθ as low as 600. However, for values of Rθ between 425 and 600, the von Ka´rma´n and additive constants vary and are shown to be functions of Rθ and shape factor H. Furthermore, the viscous sublayer in the range 425<Rθ<600 can no longer maintain its characteristically small size. It is forced to grow, due to viscous effects, into a super sublayer (6-9 percent of the boundary layer height) that greatly exceeds conventional predictions of sublayer heights.

Boundary Layers With Viscous Potential Outer Flows

Volume 1 ◽  
2004 ◽  
Author(s):  
Alireza Najafiyazdi
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Additional Term ◽  
Reynolds Numbers ◽  
Momentum Equation ◽  
Outer Flow ◽  
Bernoulli’S Equation ◽  
Momentum Integral

In this paper we try to derive improved formulations for laminar boundary layers in incompressible flows by using the concept of viscous potential flows, presented in Joseph [1] and Joseph [2], as the outer flow. Bernoulli’s equation is used at the edge of boundary layer to make the basic assumption to deduce the presented formulas. The momentum equation is derived directly from the Navier-Stokes equations and then simplified using an order of magnitude analyze. However an additional term, μ∂2u∞∂x2, remains in the momentum equation to represent the contribution of the viscosity of the outer potential flow at the edge of the boundary layer. The viscosity of the outer viscous flow shows itself also in momentum-integral and energy-integral equations. Numerical results showed that at high Reynolds numbers and low angles of attack the results of the two formulas are almost the same, but for lower Reynolds numbers and higher angles of attack the difference between the results is remarkable.

scholarly journals Turbulent boundary layers and channels at moderate Reynolds numbers

2010 ◽  
Vol 657 ◽  
pp. 335-360 ◽  
Author(s):  
JAVIER JIMÉNEZ ◽  
SERGIO HOYAS ◽  
MARK P. SIMENS ◽  
YOSHINORI MIZUNO
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Pressure Fluctuations ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Rotational Flow ◽  
Mean Velocity ◽  
The Mean ◽  
External Flows

The behaviour of the velocity and pressure fluctuations in the outer layers of wall-bounded turbulent flows is analysed by comparing a new simulation of the zero-pressure-gradient boundary layer with older simulations of channels. The 99 % boundary-layer thickness is used as a reasonable analogue of the channel half-width, but the two flows are found to be too different for the analogy to be complete. In agreement with previous results, it is found that the fluctuations of the transverse velocities and of the pressure are stronger in the boundary layer, and this is traced to the pressure fluctuations induced in the outer intermittent layer by the differences between the potential and rotational flow regions. The same effect is also shown to be responsible for the stronger wake component of the mean velocity profile in external flows, whose increased energy production is the ultimate reason for the stronger fluctuations. Contrary to some previous results by our group, and by others, the streamwise velocity fluctuations are also found to be higher in boundary layers, although the effect is weaker. Within the limitations of the non-parallel nature of the boundary layer, the wall-parallel scales of all the fluctuations are similar in both the flows, suggesting that the scale-selection mechanism resides just below the intermittent region, y/δ = 0.3–0.5. This is also the location of the largest differences in the intensities, although the limited Reynolds number of the boundary-layer simulation (Reθ ≈ 2000) prevents firm conclusions on the scaling of this location. The statistics of the new boundary layer are available from http://torroja.dmt.upm.es/ftp/blayers/.

scholarly journals A Unified Methodology to Evaluate the Radiated Noise Due to Turbulent Boundary Layer Flows

2018 ◽  
Vol 141 (6) ◽  
Author(s):  
Sylvain Morilhat ◽  
François Chedevergne ◽  
Frank Simon
Keyword(s):  
Boundary Layer ◽  
Wave Number ◽  
Frequency Range ◽  
Boundary Layer Flows ◽  
Frequency Wave ◽  
High Frequencies ◽  
Radiated Noise ◽  
Computational Methodology ◽  
Turbulent Wall ◽  
Large Frequency

For vibro-acoustic applications, a turbulent wall pressure (TWP) fluctuations model was derived. The model is based on the resolution of Poisson's equation. The pressure is characterized in time and space through its spectrum in the frequency wave-number domain. The developed model follows trends commonly observed using Corcos model in a large frequency range but also shows new behaviors for low and high frequencies. The radiated noise due to TWP fluctuations is then computed in accordance with the form of the TWP spectrum. A specific computational methodology is proposed to perform the calculation without introducing limiting hypothesis on the radiated impedance.

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