scholarly journals ASSESSMENT AND IMPROVEMENT OF COMPUTATIONAL FLUID DYNAMICS METHODS FOR SEPARATED TURBULENT FLOWS AT LOW REYNOLDS NUMBERS

2020 ◽  
Author(s):  
Tom Mancuso
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds

scholarly journals Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit

2019 ◽  
Vol 874 ◽  
pp. 699-719 ◽  
Author(s):  
Jose M. Lopez ◽  
George H. Choueiri ◽  
Björn Hof
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Pipe Flow ◽  
Domain Size ◽  
Reynolds Numbers ◽  
Weissenberg Number ◽  
Pipe Length ◽  
Low Reynolds Numbers ◽  
Maximum Drag Reduction ◽  
Low Reynolds

Polymer additives can substantially reduce the drag of turbulent flows and the upper limit, the so-called state of ‘maximum drag reduction’ (MDR), is to a good approximation independent of the type of polymer and solvent used. Until recently, the consensus was that, in this limit, flows are in a marginal state where only a minimal level of turbulence activity persists. Observations in direct numerical simulations at low Reynolds numbers ($Re$) using minimal sized channels appeared to support this view and reported long ‘hibernation’ periods where turbulence is marginalized. In simulations of pipe flow at $Re$ near transition we find that, indeed, with increasing Weissenberg number ($Wi$), turbulence expresses long periods of hibernation if the domain size is small. However, with increasing pipe length, the temporal hibernation continuously alters to spatio-temporal intermittency and here the flow consists of turbulent puffs surrounded by laminar flow. Moreover, upon an increase in $Wi$, the flow fully relaminarizes, in agreement with recent experiments. At even larger $Wi$, a different instability is encountered causing a drag increase towards MDR. Our findings hence link earlier minimal flow unit simulations with recent experiments and confirm that the addition of polymers initially suppresses Newtonian turbulence and leads to a reverse transition. The MDR state on the other hand results at these low$Re$ from a separate instability and the underlying dynamics corresponds to the recently proposed state of elasto-inertial turbulence.

scholarly journals Fluid Dynamics of Rigid and Spanwise-Flexible Elliptical Flat Plates at Low Reynolds Numbers

2010 ◽  
Author(s):  
Jonathan Rausch ◽  
Yeon Baik ◽  
Luis Bernal ◽  
Wei Shyy ◽  
Michael Ol ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Numbers ◽  
Flat Plates ◽  
Low Reynolds Numbers ◽  
Low Reynolds

A Modified Turbulence Model for Low Reynolds Numbers: Application to Hydrostatic Seals

2005 ◽  
Vol 127 (1) ◽  
pp. 130-140 ◽  
Author(s):  
Noe¨l Brunetie`re
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Turbulence Model ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Axial Stiffness ◽  
Low Reynolds Numbers ◽  
Order Of Magnitude ◽  
Low Reynolds ◽  
The Stability

A modification of the Elrod and Ng turbulence model is presented. The order of magnitude of the Reynolds number in thin lubricant films varies between 102 and 105. For Reynolds numbers higher than 103, the fluid flow becomes turbulent. It is well accepted in lubrication to use a zero-equation turbulence model of the type developed by Constantinescu (1962, ASME J. Basic Eng., 84(1), pp. 139–151), Ng (1964, ASLE Trans., 7, pp. 311–321), Ng and Pan (1965, ASME J. Basic Eng., 87, pp. 675–688), Elrod and Ng (1967, ASME J. Lubr. Technol., 89, pp. 346–362), or Hirs (1973, ASME J. Lubr. Technol., 95, pp. 137–146). The Elrod and Ng approach is certainly the most efficient for combined pressure and shear flows where the Reynolds number is above 104. This paper proposes a modification of the Elrod and Ng model in order to ensure a good correlation with experimental data obtained with low Reynolds number turbulent flows. The present model, coupled with a scaling factor for taking into account the transition to turbulence, is therefore accurate for all of the typical Reynolds number values recorded in lubrication. The model is then applied to hydrostatic noncontacting face seals, which usually operate at Reynolds numbers varying from 103 to 104. The accuracy of the model is shown for this particular application of radial rotating flow. A special study is made of the transition to turbulence. The results are compared with those obtained using the initial Elrod and Ng model. The axial stiffness coefficient and the stability threshold are significantly affected by the turbulence model.

A Modified Turbulence Model for Low Reynolds Numbers: Applications to Hydrostatic Seals

2004 ◽  
Author(s):  
Noe¨l Brunetie`re
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Turbulence Model ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Axial Stiffness ◽  
Low Reynolds Numbers ◽  
Order Of Magnitude ◽  
Low Reynolds ◽  
The Stability

The order of magnitude of the Reynolds number in thin lubricant films varies between 102 and 105. For Reynolds numbers higher than 103, the fluid flow becomes turbulent. It is well accepted in lubrication to use a zero equation turbulence model of the type developed by Constantinescu [1] or Elrod, Ng and Pan [2–4] or Hirs [5]. The Elrod and Ng approach is certainly the most efficient for combined pressure and shear flows where the Reynolds number is above 104. This paper proposes a modification of the Elrod and Ng model in order to ensure a good correlation with experimental data obtained with low Reynolds number turbulent flows. The present model, coupled with a scaling factor for taking into account the transition to turbulence, is therefore accurate for all the typical Reynolds number values recorded in lubrication. The model is then applied to hydrostatic noncontacting face seals, which usually operate at Reynolds numbers varying from 103 to 104. The accuracy of the model is shown for this particular application of radial rotating flow. A special study is made of the transition to turbulence. The results are compared with those obtained using the initial Elrod and Ng model. The axial stiffness coefficient and the stability threshold are significantly affected by the turbulence model.

Using Computational Fluid Dynamics to Design Heat Transfer Enhancement Methods for Cooling Channels

1995 ◽  
Author(s):  
Aaron M. Plotnik ◽  
Ann M. Anderson
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Low Reynolds Numbers ◽  
Cooling Channels ◽  
Dimensional Measure

Abstract This paper presents the results of a study to enhance heat transfer in a short narrow cooling channel (7.9 mm high by 30.9 mm wide by 109 mm long). The study was performed using a computational fluid dynamics (CFD) code. Flotherm, by Flomerics, Inc. The work emphasizes the usefulness of CFD in the design process. The heat transfer enhancement was accomplished by placing thin rib-like protrusions in the channel. Simulations were run for two protrusion spacings, with a range of protrusion heights from 0.5 to 1.5 mm and a range of channel Reynolds number from 500 to 40,000. The results of a grid dependence study are presented and baseline comparisons are made to validate the computational model. The results show increases in channel Nusselt number of 10–160% while the friction factor increases by 10–5200%. The different configurations are compared using a non-dimensional measure of the pumping power and this shows that devices are most effective at low Reynolds numbers. The enhancement in heat transfer, the increase in friction loss and the worth in terms of pumping power would all have to be weighed with respect to the needs of a particular application before any choice is made to apply the techniques studied in this report.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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