Direct Numerical Simulations of the Free, Unsteady, Round, Unforced Jet at Low Reynolds Numbers

Direct numerical simulations of passive scalars, with Prandtl numbers Pr=3, 5, and 7, advected by turbulence at three low Reynolds numbers were performed. The energy spectra are self-similar under the Kolmogorov scaling and exhibit behaviour consistent with many other investigations: a short inertial range for the highest Reynolds number and the universal exponential form of the spectrum for all Reynolds numbers in the dissipation range. In all cases the passive scalar spectra collapse to a single self-similar curve under the Batchelor scaling and exhibit the k−1 range followed by an exponential fall-off. We attribute the applicability of the Batchelor scaling to our low-Reynolds-number flows to the universality of the energy dissipation spectra. The Batchelor range is observed for wavenumbers in general agreement with experimental observations but smaller than predicted by the classical estimates. The discrepancy is caused by the fact that the velocity scales responsible for the generation of the Batchelor range are in the vicinity of the wavenumber of the maximum energy dissipation, which is one order of magnitude less than the Kolmogorov wavenumber used in the classical theory. Two different functional forms of passive scalar spectra proposed by Batchelor and Kraichnan were fitted to the simulation results and it was found that the Kraichnan model agrees very well with the data while the Batchelor formula displays systematic deviations from the data. Implications of these differences for the experimental procedures to measure the energy and passive scalar dissipation rates in oceanographic flows are discussed.

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

Mechanics & Industry ◽

10.1051/meca/2020095 ◽

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.

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

International Review of Applied Sciences and Engineering ◽

10.1556/irase.1.2010.1-2.3 ◽

2010 ◽

Vol 1 (1-2) ◽

pp. 15-20 ◽

Cited By ~ 1

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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