Suresh Menon

LES of spray combustion in swirling flows

The ability to predict turbulence-chemistry interactions in realistic full-scale gas turbine combustors has not been feasible until now due to the lack of simulation models and computing power. Her...

Linear eddy simulations of Reynolds number and Schmidt number effects on turbulent scalar mixing

Effects of molecular diffusion on turbulent scalar mixing are studied using the linear eddy model. Unlike the energy spectrum which is determined only by the viscous and eddy time scales, the scalar spectra also depend on the diffusion time scales. The linear eddy model, being one-dimensional, offers an inexpensive way of capturing these time scale dependencies. Some of the observations made using experiments and direct simulations are verified using the model. Simulations reported here indicate that certain features of scalar mixing continue to depend on the Reynolds number (Reλ) and the Schmidt number (Sc) in the range of parameter space (32⩽Reλ⩽775 and 0.001⩽Sc⩽700) that is unattainable using the current direct simulation capabilities. However, some of the models developed for differential diffusion using direct simulations are shown to be accurate even when the difference in the Schmidt numbers of the scalars and (or) the Reynolds numbers are very high.

On Richtmyer–Meshkov instability in dilute gas-particle mixtures

Richtmyer–Meshkov instability (RMI) in gas-particle mixtures is investigated both numerically and analytically. The linear amplitude growth rate for a RMI in a two-phase mixture is derived by using a dusty gas formulation for small Stokes number (St⪡1.0), and it is shown that the problem can be characterized by mass loading and St. The model predictions are compared with numerical results under two conditions, i.e., a shock wave hitting (1) a perturbed species interface of air and SF6 surrounded by uniformly distributed particles, and (2) a perturbed shape particle cloud in uniform air. In the first case, the interaction between the instability of the species perturbation and the particles is investigated. The multiphase growth model accurately predicts the growth rates when St⪡1.0, and the amplitude growth normalized by the two-phase RMI velocity shows good agreement with the single-phase RMI growth rate as well. It is also shown that the two-phase model results are in accordance with the growth rates ob...

Large‐eddy simulations of axisymmetric excitation effects on a row of impinging jets

Numerical simulations of a row of impinging jets are performed. Both the impinging jets and the fountains caused by the collision of the wall jets are modeled in the simulation. The problem considered contains the essential features of twin jets impinging on the ground, simulating the hovering configuration of a vertical takeoff and landing (VTOL) aircraft. The flow is assumed to be governed by the time‐dependent, incompressible Navier–Stokes equations. The large‐eddy simulation approach is followed. The present study focuses on the motion and dynamics of large‐scale structures that have been experimentally observed in jet flows. The behavior of the jets and the fountain caused by the introduction of axisymmetric disturbances at the jet exits are investigated.

Richtmyer-Meshkov instability in dilute gas-particle mixtures with re-shock

The Richtmyer-Meshkov instability (RMI) is investigated in a dilute gas-particle mixture using three-dimensional numerical simulations. This work extends an earlier two-dimensional study [S. Ukai, K. Balakrishnan, and S. Menon, “On Richtmyer-Meshkov instability in dilute gas-particle mixtures,” Phys. Fluids 22, 104103 (2010)] to a larger parameter space consisting of variations in the mass loading and the particle size as well as considering both single-mode and multi-mode interface initializations. In addition, the effect of the presence of particles on re-shock RMI is also investigated. Single-phase numerical predictions of the mixing layer growth-rate are shown to compare well to both experimental and theoretical results. In a dilute gas-particle mixture, the initial growth-rate of RMI shows similar trends compared to previous work; however, the current numerical predictions show that there is an observable increase, not previously predicted, in the growth of the mixing layer at higher mass loadings. F...

Large‐eddy simulations of excitation effects on a VTOL upwash fountain

The responses of an upwash fountain to various azimuthal and axisymmetric excitations, applied at the exits of its neighboring jets, are investigated. Kinematic arguments are used to determine the interactions of large‐scale structures in the fountain and the effects of these interactions on the fountain’s characteristics. Numerical simulations of a row of impinging jets, which contain the essential features of twin jets impinging on the ground, are used to simulate the hovering configuration of a vertical takeoff and landing (VTOL) aircraft. The flow is assumed to be governed by the time‐dependent, incompressible Navier–Stokes equations. The large‐eddy simulation approach is followed. Distinct fountain characteristics are shared among the cases in which azimuthal perturbations are applied at both jet exits in the same direction. These include a high fountain spreading rate, a strong lateral interaction with the neighboring jets, and a weak upload at the aircraft’s undersurface. A strong similarity in fou...

On the application of the two-level large-eddy simulation method to turbulent free-shear and wake flows

We present application of the hybrid two-level large-eddy simulation (TLS-LES) method, a multi-scale simulation model, to turbulent free-shear and wake flows at moderately high Reynolds number. The TLS-LES method combines the scale-separation-based two-level simulation (TLS) model with the spatial-filtering-based conventional large-eddy simulation (LES) model in an additive manner using a normalised blending function. The additive blending can be performed in a static or a dynamic manner. We demonstrate that the method, which has been originally developed for wall-bounded flows, can be used to simulate flows in complex configurations without requiring any further adjustments to the model. In this study, three canonical flows are simulated, which are representative of free-shear and wake flows. These cases include a temporally evolving mixing layer, flow past a circular cylinder in a uniform flow and flow past a finite-span airfoil placed in a uniform flow at three different angle of attacks. We analyse the role of static and dynamic blending functions, large-scale grid resolution and the effect of small scales on the instantaneous flow features and turbulence statistics. The results obtained from these cases demonstrate robustness, accuracy and consistency of the multi-scale TLS-LES method and show that the method is suitable for investigation of turbulent flows that encompass features such as massive separation, reattachment, transition to turbulence and unsteady wake, which are challenging to model numerically.

An investigation of axisymmetric excitation effects on a row of impinging jets using large-eddy simulations

Numerical simulations of a row of impinging jets are performed. Both the impinging jets and the fountains caused by the collision of the wall jets are modeled in the simulations. The problem considered contains the essential features of twin jets impinging on the ground, simulating the hovering configuration of a vertical takeoff and landing (VTOL) aircraft. The flow is assumed to be governed by the time-dependent, incompressible Navier-Stokes equations. The large-eddy simulation approach is followed. The present study focuses on the motion and dynamics of large-scale structures that have been experimentally observed in jet flows. The behavior of the jets and the fountain due to the introduction of axisymmetric disturbances at the jet exits is investigated.