scholarly journals Secondary motion in turbulent pipe flow with three-dimensional roughness

2018 ◽  
Vol 854 ◽  
pp. 5-33 ◽  
Author(s):  
L. Chan ◽  
M. MacDonald ◽  
D. Chung ◽  
N. Hutchins ◽  
A. Ooi
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Secondary Flows ◽  
Turbulent Pipe Flow ◽  
Roughness Height ◽  
Stress Profile ◽  
Roughness Elements ◽  
Secondary Motion ◽  
Proportional Increase

The occurrence of secondary flows is investigated for three-dimensional sinusoidal roughness where the wavelength and height of the roughness elements are systematically altered. The flow spanned from the transitionally rough regime up to the fully rough regime and the solidity of the roughness ranged from a wavy, sparse roughness to a dense roughness. Analysing the time-averaged velocity, secondary flows are observed in all of the cases, reflected in the coherent stress profile which is dominant in the vicinity of the roughness elements. The roughness sublayer, defined as the region where the coherent stress is non-zero, scales with the roughness wavelength when the roughness is geometrically scaled (proportional increase in both roughness height and wavelength) and when the wavelength increases at fixed roughness height. Premultiplied energy spectra of the streamwise velocity turbulent fluctuations show that energy is reorganised from the largest streamwise wavelengths to the shorter streamwise wavelengths. The peaks in the premultiplied spectra at the streamwise and spanwise wavelengths are correlated with the roughness wavelength in the fully rough regime. Current simulations show that the spanwise scale of roughness determines the occurrence of large-scale secondary flows.

Structural organization of large and very large scales in turbulent pipe flow simulation

2013 ◽  
Vol 720 ◽  
pp. 236-279 ◽  
Author(s):  
J. R. Baltzer ◽  
R. J. Adrian ◽  
Xiaohua Wu
Keyword(s):  
Turbulent Flows ◽  
Pipe Flow ◽  
Velocity Fluctuation ◽  
Large Scale ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Streamwise Velocity ◽  
Turbulent Pipe Flow ◽  
Low Velocity ◽  
Logarithmic Layer

AbstractThe physical structures of velocity are examined from a recent direct numerical simulation of fully developed incompressible turbulent pipe flow (Wu, Baltzer & Adrian, J. Fluid Mech., vol. 698, 2012, pp. 235–281) at a Reynolds number of ${\mathit{Re}}_{D} = 24\hspace{0.167em} 580$ (based on bulk velocity) and a Kármán number of ${R}^{+ } = 685$. In that work, the periodic domain length of $30$ pipe radii $R$ was found to be sufficient to examine long motions of negative streamwise velocity fluctuation that are commonly observed in wall-bounded turbulent flows and correspond to the large fractions of energy present at very long streamwise wavelengths (${\geq }3R$). In this paper we study how long motions are composed of smaller motions. We characterize the spatial arrangements of very large-scale motions (VLSMs) extending through the logarithmic layer and above, and we find that they possess dominant helix angles (azimuthal inclinations relative to streamwise) that are revealed by two- and three-dimensional two-point spatial correlations of velocity. The correlations also reveal that the shorter, large-scale motions (LSMs) that concatenate to comprise the VLSMs are themselves more streamwise aligned. We show that the largest VLSMs possess a form similar to roll cells centred above the logarithmic layer and that they appear to play an important role in organizing the flow, while themselves contributing only a minor fraction of the flow turbulent kinetic energy. The roll cell motions play an important role with the smaller scales of motion that are necessary to create the strong streamwise streaks of low-velocity fluctuation that characterize the flow.

Space–time formation of very-large-scale motions in turbulent pipe flow

2019 ◽  
Vol 881 ◽  
pp. 1010-1047 ◽  
Author(s):  
Jae Hwa Lee ◽  
Hyung Jin Sung ◽  
Ronald J. Adrian
Keyword(s):  
Pipe Flow ◽  
Large Scale ◽  
Spatial Organization ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Turbulent Pipe Flow ◽  
Strain Component ◽  
Spatial Correlations ◽  
Correlation Pattern ◽  
Using Data

We examine the origin of very-large-scale motions (VLSMs) in fully developed turbulent pipe flow at friction Reynolds number, $\mathit{Re}_{\unicode[STIX]{x1D70F}}=934$, using data from a direct numerical simulation. The VLSMs and the packet-like large-scale motions (LSMs) found in this study are very similar to those found in earlier studies. Three-dimensional time-evolving instantaneous fields show that one component of the process leading to the large streamwise length of VLSMs is the concatenation of adjacent streamwise LSMs caused by the continuous elongation of LSMs due to the strain component of the mean shear. Spatial organization patterns of the VLSMs and LSMs and their properties are studied by separating auto-correlation of the streamwise velocity fluctuations into the components of the VLSM and the LSM defined by low-pass/high-pass filtering in the streamwise direction. The structures of the two-point spatial correlations of the streamwise velocity component of the VLSMs and the LSMs in the streamwise-azimuthal plane are characterized by multiple maxima and complex patterns that beg explanation in terms of patterned coherent arrangements of the LSMs. Using proper orthogonal decomposition (POD), it is found that the X-shape correlation pattern of the VLSMs results from the superposition of very long helically inclined structures and streamwise-aligned structures. Further explanation of the patterns in the correlations of the VLSMs and LSMs is provided through the study of synthetically constructed arrangements of simple hairpin packet models of the LSM. Head-to-tail alignment of the model packets along streamwise and helical directions suggested by the eigenvalues of the POD creates a pair of long roll-cells centred above the logarithmic layer, and bracketing the LSMs. These roll-cells are pure kinematic consequences of the induction within the LSM packets, but they may also serve to organize smaller packets.

scholarly journals The Design of an Improved Endwall Film-Cooling Configuration

1998 ◽  
Author(s):  
S. Friedrichs ◽  
H. P. Hodson ◽  
W. N. Dawes
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Large Scale ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Aerodynamic Loss ◽  
Cooling Flow ◽  
High Static Pressure ◽  
Endwall Film Cooling ◽  
Aerodynamic Losses

The endwall film-cooling cooling configuration investigated by Friedrichs et al. (1996, 1997) had in principle sufficient cooling flow for the endwall, but in practice, the redistribution of this coolant by secondary flows left large endwall areas uncooled. This paper describes the attempt to improve upon this datum cooling configuration by redistributing the available coolant to provide a better coolant coverage on the endwall surface, whilst keeping the associated aerodynamic losses small. The design of the new, improved cooling configuration was based on the understanding of endwall film-cooling described by Friedrichs et al. (1996, 1997). Computational fluid dynamics were used to predict the basic flow and pressure field without coolant ejection. Using this as a basis, the above described understanding was used to place cooling holes so that they would provide the necessary cooling coverage at minimal aerodynamic penalty. The simple analytical modelling developed in Friedrichs et al. (1997) was then used to check that the coolant consumption and the increase in aerodynamic loss lay within the limits of the design goal. The improved cooling configuration was tested experimentally in a large scale, low speed linear cascade. An analysis of the results shows that the redesign of the cooling configuration has been successful in achieving an improved coolant coverage with lower aerodynamic losses, whilst using the same amount of coolant as in the datum cooling configuration. The improved cooling configuration has reconfirmed conclusions from Friedrichs et al. (1996, 1997); firstly, coolant ejection downstream of the three-dimensional separation lines on the endwall does not change the secondary flow structures; secondly, placement of holes in regions of high static pressure helps reduce the aerodynamic penalties of platform coolant ejection; finally, taking account of secondary flow can improve the design of endwall film-cooling configurations.

Analysis of Buoyancy and Tube Rotation Relative to the Modified Chemical Vapor Deposition Process

1990 ◽  
Vol 112 (4) ◽  
pp. 1063-1069 ◽  
Author(s):  
M. Choi ◽  
Y. T. Lin ◽  
R. Greif
Keyword(s):  
Secondary Flow ◽  
Vapor Deposition ◽  
Particle Deposition ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Horizontal Tube ◽  
Deposition Process ◽  
Secondary Flows ◽  
Secondary Motion

The secondary flows resulting from buoyancy effects in respect to the MCVD process have been studied in a rotating horizontal tube using a perturbation analysis. The three-dimensional secondary flow fields have been determined at several axial locations in a tube whose temperature varies in both the axial and circumferential directions for different rotational speeds. For small rotational speeds, buoyancy and axial convection are dominant and the secondary flow patterns are different in the regions near and far from the torch. For moderate rotational speeds, the effects of buoyancy, axial and angular convection are all important in the region far from the torch where there is a spiraling secondary flow. For large rotational speeds, only buoyancy and angular convection effects are important and no spiraling secondary motion occurs far downstream. Compared with thermophoresis, the important role of buoyancy in determining particle trajectories in MCVD is presented. As the rotational speed increases, the importance of the secondary flow decreases and the thermophoretic contribution becomes more important. It is noted that thermophoresis is considered to be the main cause of particle deposition in the MCVD process.

Three-dimensional instabilities in steady and unsteady non-parallel boundary layers, including effects of Tollmien-Schlichting disturbances and cross flow

1987 ◽  
Vol 409 (1837) ◽  
pp. 229-248 ◽  
Keyword(s):  
Boundary Layers ◽  
Large Scale ◽  
Three Dimensional ◽  
Steady Motion ◽  
Cross Flow ◽  
Parallel Flows ◽  
Roughness Elements ◽  
Tollmien Schlichting ◽  
Flow Effects ◽  
Secondary Instabilities

Three-dimensional (3D) linear stability properties are considered for steady and unsteady 2D or 3D boundary layers with significant non-parallelism present. Two main examples of such non-parallel flows whose stability is of interest are, firstly, steady motion, over roughness elements, in cross flow, or in large-scale separation and, secondly, unsteady 2D Tollmien-Schlichting (TS) motion, with its associated question of secondary instabilities. A high-frequency stability analysis is presented here. It is found that, for 2DTS or steady boundary layers, there is a swing in the direction of maximum TS spatial growth rate, from 0° for parallel flow towards 64.68° away from the free-stream direction, as the nonparallel flow effects increase. These effects then depend principally on, and indeed are proportional to, the local slope of the boundary-layer displacement. Cross flow can also have a profound impact on TS instabilities. Further implications for higher-amplitude and/or fasterscale disturbances, their secondary instability, and nonlinear interactions, are also discussed.

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

2011 ◽  
Vol 673 ◽  
pp. 255-285 ◽  
Author(s):  
N. HUTCHINS ◽  
J. P. MONTY ◽  
B. GANAPATHISUBRAMANI ◽  
H. C. H. NG ◽  
I. MARUSIC
Keyword(s):  
Skin Friction ◽  
High Reynolds Number ◽  
Large Scale ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Small Scale ◽  
Large Scale Structures ◽  
Local Mean ◽  
Scale Structures ◽  
High Reynolds

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly amplified. In general, it is observed that the attenuation and amplification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions.

Heat Transfer Enhancement in Narrow Channels Using Two and Three-Dimensional Mixing Devices

1995 ◽  
Vol 117 (3) ◽  
pp. 590-596 ◽  
Author(s):  
S. V. Garimella ◽  
D. J. Schlitz
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Prandtl Number ◽  
Heat Transfer Enhancement ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Transitional Flow ◽  
Transfer Enhancement ◽  
Roughness Elements

The localized enhancement of forced convection heat transfer in a rectangular duct with very small ratio of height to width (0.017) was experimentally explored. The heat transfer from a discrete square section of the wall was enhanced by raising the heat source off the wall in the form of a protrusion. Further enhancement was effected through the use of large-scale, three-dimensional roughness elements installed in the duct upstream of the discrete heat source. Transverse ribs installed on the wall opposite the heat source provided even greater heat transfer enhancement. Heat transfer and pressure drop measurements were obtained for heat source length-based Reynolds numbers of 2600 to 40,000 with a perfluorinated organic liquid coolant, FC-77, of Prandtl number 25.3. Selected experiments were also performed in water (Prandtl number 6.97) for Reynolds numbers between 1300 and 83,000, primarily to determine the role of Prandtl number on the heat transfer process. Experimental uncertainties were carefully minimized and rigorously estimated. The greatest enhancement in heat transfer relative to the flush heat source was obtained when the roughness elements were used in combination with a single on the opposite wall. A peak enhancement of 100 percent was obtained at a Reynolds number of 11,000, which corresponds to a transitional flow regime. Predictive correlations valid over a range of Prandtl numbers are proposed.

Analysis of a LPT Rotor Blade for a Geared Engine: Part II — Characterization of the Time-Varying Flow Field in a Single Stage Research Turbine

2016 ◽  
Author(s):  
Daniele Infantino ◽  
Francesca Satta ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
...  
Keyword(s):  
Flow Field ◽  
Rotor Blade ◽  
Large Scale ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Single Stage ◽  
Tip Vortex ◽  
Time Dependent ◽  
Exit Plane ◽  
Open Rotor

The present paper is the second part of a two-part paper focused on the design and the analysis of an optimized rotor blade for a geared open rotor engine. This part is focused on the experimental investigation of the three-dimensional unsteady flow field at the exit plane of a rotor row installed in a large scale single-stage low speed research turbine. The investigation is aimed at in depth characterizing the wake-boundary layer and the vortex-vortex interaction processes induced by the rotor-stator relative motion. Measurements have been carried out at a typical aeroengine cruise condition Reynolds number. The rotor blade aerodynamic loadings at different blade spans have been measured. A five-hole probe has been used to assess the row efficiency and detailed hot-wire phase-locked ensemble-averaged data have been analyzed to characterize the three-dimensional time-dependent flow field at the rotor exit plane. Results clearly highlight a significant distortion of the rotor blade wake and tip vortex during the migration of the high turbulence regions (wake and secondary flows) associated with the upstream stator. The unsteady interaction between the stator secondary flows and the rotor passage vortex provokes a time dependent movement of the low momentum area at the hub surface, sensibly modifying the penetration of the rotor secondary flows in an incoming stator wake passage period. The comparison of deterministic and random velocity fluctuations also allows the distinction between the structures generated by the stator and those due to the rotor.

Partially filled pipes: experiments in laminar and turbulent flow

2018 ◽  
Vol 848 ◽  
pp. 467-507 ◽  
Author(s):  
Henry C.-H. Ng ◽  
Hope L. F. Cregan ◽  
Jonathan M. Dodds ◽  
Robert J. Poole ◽  
David J. C. Dennis
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Turbulent Flow ◽  
Pipe Flow ◽  
Large Scale ◽  
Open Channel ◽  
Streamwise Velocity ◽  
Flow Depth ◽  
Secondary Motion ◽  
Laminar And Turbulent Flow

Pressure-driven laminar and turbulent flow in a horizontal partially filled pipe was investigated using stereoscopic particle imaging velocimetry (S-PIV) in the cross-stream plane. Laminar flow velocity measurements are in excellent agreement with a recent theoretical solution in the literature. For turbulent flow, the flow depth was varied independently of a nominally constant Reynolds number (based on hydraulic diameter, $D_{H}$; bulk velocity, $U_{b}$ and kinematic viscosity $\unicode[STIX]{x1D708}$) of $Re_{H}=U_{b}D_{H}/\unicode[STIX]{x1D708}\approx 30\,000\pm 5\,\%$. When running partially full, the inferred friction factor is no longer a simple function of Reynolds number, but also depends on the Froude number $Fr=U_{b}/\sqrt{gD_{m}}$ where $g$ is gravitational acceleration and $D_{m}$ is hydraulic mean depth. S-PIV measurements in turbulent flow reveal the presence of secondary currents which causes the maximum streamwise velocity to occur below the free surface consistent with results reported in the literature for rectangular cross-section open channel flows. Unlike square duct and rectangular open channel flow the mean secondary motion observed here manifests only as a single pair of vortices mirrored about the vertical bisector and these rollers, which fill the half-width of the pipe, remain at a constant distance from the free surface even with decreasing flow depth for the range of depths tested. Spatial distributions of streamwise Reynolds normal stress and turbulent kinetic energy exhibit preferential arrangement rather than having the same profile around the azimuth of the pipe as in a full pipe flow. Instantaneous fields reveal the signatures of elements of canonical wall-bounded turbulent flows near the pipe wall such as large-scale and very-large-scale motions and associated hairpin packets whilst near the free surface, the signatures of free surface turbulence in the absence of imposed mean shear such as ‘upwellings’, ‘downdrafts’ and ‘whirlpools’ are present. Two-point spatio-temporal correlations of streamwise velocity fluctuation suggest that the large-scale coherent motions present in full pipe flow persist in partially filled pipes but are compressed and distorted by the presence of the free surface and mean secondary motion.

Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

2016 ◽  
Vol 796 ◽  
pp. 158-194 ◽  
Author(s):  
Holger B. E. Kurz ◽  
Markus J. Kloker
Keyword(s):  
Boundary Layer ◽  
Roughness Element ◽  
Three Dimensional ◽  
Finite Size ◽  
Roughness Height ◽  
Swept Wing ◽  
Global Instability ◽  
Critical Height ◽  
Roughness Elements ◽  
Dimensional Boundary

The effects of a spanwise row of finite-size cylindrical roughness elements in a laminar, compressible, three-dimensional boundary layer on a wing profile are investigated by direct numerical simulations (DNS). Large elements are capable of immediately tripping turbulent flow by either a strong, purely convective or an absolute/global instability in the near wake. First we focus on an understanding of the steady near-field past a finite-size roughness element in the swept-wing flow, comparing it to a respective case in unswept flow. Then, the mechanisms leading to immediate turbulence tripping are elaborated by gradually increasing the roughness height and varying the disturbance background level. The quasi-critical roughness Reynolds number above which turbulence sets in rapidly is found to be $Re_{kk,qcrit}\approx 560$ and global instability is found only for values well above 600 using nonlinear DNS; therefore the values do not differ significantly from two-dimensional boundary layers if the full velocity vector at the roughness height is taken to build $Re_{kk}$. A detailed simulation study of elements in the critical range indicates a changeover from a purely convective to a global instability near the critical height. Finally, we perform a three-dimensional global stability analysis of the flow field to gain insight into the early stages of the temporal disturbance growth in the quasi-critical and over-critical cases, starting from a steady state enforced by damping of unsteady disturbances.

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