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The three-dimensional flow around a custom wing performing pitching oscillation is analyzed numerically using large-eddy simulation with the wall adapting local eddy-viscosity subgrid-scale model. The wake characteristics behind the pitching wing with three different aspect ratios, AR = 2 / 3 , 1 , 4 / 3 , is investigated in an upstream flow with Reynolds number, Re = 2640. The Q − function is employed to identify the swirling structures in the flow field, and four primary vortices, namely, primary leading edge vortex (PLEV), secondary leading edge vortex, wing tip vortices, and trailing edge vortex, are identified. The evolution of vortices over the wing surface is presented in detail, and the arrangement of vortex rings in the wake is compared for three different aspect ratios. The PLEV develops into an arch vortex using the self-induction phenomenon, and the interlinking between the subsequent vortex rings depends on the arch vortex leaving the trailing edge. The force coefficient computed over the wing shows a positive thrust for AR = 4 / 3. The mean velocity field contours indicate a spanwise loading on the wing, which is unaccountable in two-dimensional studies. The Reynolds stresses generated due to large-scale periodic velocity fluctuations in the wake are presented. The vorticity field in the midplane of the wing appears to be diffusive at higher aspect ratios. The comparison of vorticity from the three-dimensional and two-dimensional models suggests that a two-dimensional model will over predict the vorticity distribution and force coefficients in the wake. [ABSTRACT FROM AUTHOR]

The wake dynamics behind a sinusoidally pitching custom designed symmetrical airfoil is analyzed computationally. The effect of pitching frequency and pitching amplitude is investigated independently at a constant Reynolds number. The wake patterns are found to exhibit a transition from von Karman to reverse von Karman vortex street and from symmetric reverse von Karman vortex street to asymmetric deflected wake as established. For laminar flow under investigation, the contours of time-varying velocity fluctuations are presented. The mean profiles of velocity and the fluctuations at different locations in the wake show that the thrust wakes are generated at the expense of energy of the surrounding fluid. The temporal behavior of the flow field is analyzed using the phase plot. The time series plots of force coefficients show a periodic loading on the airfoil. Proper orthogonal decomposition (POD) analysis of drag, neutral and thrust wakes displayed the evolution of coherent structures in the flow field. The evolution of these structures portray the transitions in the wake of the airfoil. The merging of coherent structures in an asymmetric deflected wake turns out to be an efficient way of identifying the location of deflection. • The vortex pairing mechanism is identified for the deflected wake. • The time average of fluctuating quantities are evaluated to quantify flow field. • The chaotic behavior of the flow field is identified using the u − v phase plot. • Time series analysis shows the effect of frequency is more prominent on force coefficients. • The coherent structures are identified using Proper orthogonal decomposition. [ABSTRACT FROM AUTHOR]

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the k - ϵ , k - ω , SST k - ω , cubic k - ϵ and quadratic k - ϵ models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the k - ϵ , quadratic k - ϵ and SST k - ω models give more unsatisfactory results for the investigated configuration, while the cubic k - ϵ model is capable of predicting the local Nusselt number in wall-jet region only. The k - ω model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the k - ω model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination (ϕ = 5 0 ∘ , 7 0 ∘ and 9 0 ∘ ), jet-to-surface distance ( d L = 4 , 6 and 8), Reynolds number (Re = 1 2 0 0 0 , 15 000 and 20 000), and turbulent intensity (I = 5 % , 7. 5 % and 1 0 %) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of ϕ decreases, the point of maximum Nusselt number ( Nu max ) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the Nu max is found to be independent of Re and d L within the range considered for the study. [ABSTRACT FROM AUTHOR]

A dimensionless numerical investigation of turbulent flow and heat transfer characteristics due to the impingement of a free inclined slot jet onto the moving hot surface has been performed using the k − ω turbulence model. The parameters considered for the investigation are: the Reynolds number, impingement angle and plate velocity. The influence of parameters on the properties such as the pressure and velocity profiles, skin-friction coefficients, Nusselt number, interface temperature, and the location of stagnation has been presented. The displacement of stagnation point depends primarily on ϕ , whereas the effect of plate velocity is less significant. These relocations are found in between X = − 2 to 0. The effect of plate velocity on average skin-friction coefficient is continuously decreasing with increase in jet angle. A continuous increase in average Nu has been found with increase in Re for all values of ϕ and U p considered in the present study. It is revealed that the change in plate velocity has more influence on the average Nu for lower angles of impingement. Further reduction in the impingement angle shows an adverse effect on the average Nu. Correlations have been developed for Nusselt number at different zones based on the parameters considered for the study. [ABSTRACT FROM AUTHOR]

Large eddy simulation (LES) with dynamic Smagorinsky model (DSM) has been implemented to elicit the turbulence characteristic of the flow inside a cubic lid-driven cavity at Reynolds number of 10000. The coherent organized structures tear, pair and disintegrate leading to the evolution of turbulence. They are reflected in the RMS (root mean square) plots of the turbulent fluctuations in different planes. The flow has a near zero helicity value; unlike the other two velocity component, the probability density function of span wise velocity component shows the flow symmetry on the both side of the mid plane in span wise direction; kurtosis being largely leptokurtic except near wall locations indicates their peakedness. The quadrant analysis shows presence of more coherent structures near the down stream wall and the joint probability distribution function shows that turbulence is anisotropic. Power spectra is observed to follow the − 5 ∕ 3 law. Both Taylor microscale λ and Kolmogorov length scale η show greater near-wall dissipation • Large eddy simulation of cubic lid-driven cavity flow has been performed at Re =10000. • Q- criterion shows the coherent organized structures tear, pair and disintegrate leading to the evolution of turbulence. • The Fourier spectra of auto correlation shows a slope of − 5 ∕ 3 in the sub inertial range. • The probability density function of span wise velocity component on the symmetrical mid plane shows the flow maintains symmetry even at high Reynolds number and has very low skewness value. Kurtosis is mostly leptokurti except near wall location. • Joint probability density function shows the turbulent fluctuations distribution is anisotropic. [ABSTRACT FROM AUTHOR]

A detailed study of a three-dimensional spatially developing planar turbulent jet has been carried out by large eddy simulation (LES). The jet Reynolds number is 4000 based on the inlet velocity and jet width. The dynamic Smagorinsky model (DSM) is used to resolve the subgrid scale stress tensor. The transition from laminar to turbulent flow has been numerically identified and discussed in details. The evolution of vortex roll ups, their transportation and final disintegration to smaller vortices have been visualized by the plot of isosurface of Q criterion. The coherent structures in a turbulent planar jet have been well demonstrated. The time series plots of λ 2 criterion shows the swirl and shear nature of the evolving vortices and their passage in the downstream. The time averaged velocity at far downstream ( x D = 10 and 15) shows a self-similarity behavior where the flow has established a fully turbulent nature. The energy spectra are shown to exhibit the −5/3 power law. The proper orthogonal decomposition (POD) shows that 90% of the fluctuating kinetic energy is contained within the first 100 modes. The probability density function on the centerline ( y D = 15 and z D = 2.5 ) for different x D locations are plotted and the corresponding skewness and kurtosis values are reported for u ̄ , v ̄ , w ̄ and p ̄ . [ABSTRACT FROM AUTHOR]