The application of the Immersed Boundary (IB) method to simulate incompressible, turbulent flows around complex configurations is illustrated; IB based on use non-body conformal grids, and effect presence a body in flow accounted for by modifying governing equations. Turbulence modeled using standard Reynolds-Averaged Navier-Stokes models or more sophisticated Large Eddy Simulation approach. main features technique are described with emphasis treatment boundary conditions at an immersed...

We present a numerical scheme geared for high performance computation of wall-bounded turbulent flows. The number all-to-all communications is decreased to only six instances by using two-dimensional (pencil) domain decomposition and utilizing the favourable scaling CFL time-step constraint as compared diffusive constraint. As condition more restrictive at driving, implicit time integration viscous terms in wall-parallel directions no longer required. This avoids communication non-local...

To quantify the fate of respiratory droplets under different ambient relative humidities, direct numerical simulations a typical event are performed. We found that, because small (with initial diameter $10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) swept by turbulent eddies in expelled humid puff, their lifetime gets extended factor more than 30 times as compared to what is suggested classical picture Wells, for 50% humidity. With increasing humidity extension lifetimes further increases...

Immersed boundary methods (IBMs) are versatile and efficient computational techniques to solve flow problems in complex geometric configurations that retain the simplicity efficiency of Cartesian structured meshes. Although these became known 1970s gained credibility only new millennium, they had already been conceived implemented at beginning 1960s, even if early computers those times did not allow researchers exploit their potential. Nowadays IBMs established numerical schemes employed for...

Numerical experiments are conducted to study high-Rayleigh-number convective turbulence ($Ra$ ranging from $2\times 10^6$ up 10^{11}$) in a $\Gamma=1/2$ aspect-ratio cylindrical cell heated below and cooled above filled with gaseous helium ($Pr=0.7$). The numerical approach allows three-dimensional velocity, vorticity temperature fields be analysed. Furthermore, several probes placed within the fluid volume, permitting point-wise velocity time series extracted. Taking advantage of data...

Results from direct numerical simulation (DNS) for three-dimensional Rayleigh–Bénard convection in a cylindrical cell of aspect ratio 1/2 and Prandtl number Pr =0.7 are presented. They span five decades Rayleigh Ra 2 × 10 6 to 11 . The results good agreement with the experimental data Niemela et al ( Nature , vol. 404, 2000, p. 837). Previous DNS Amati Phys. Fluids 17, 2005, paper no. 121701) showed heat transfer that was up 30% higher than values. simulations presented this performed much...

Experimental and numerical data for the heat transfer as a function of Rayleigh, Prandtl, Rossby numbers in turbulent rotating Rayleigh-B\'enard convection are presented. For relatively small $\mathrm{Ra}\ensuremath{\approx}{10}^{8}$ large Pr modest rotation can enhance by up to 30%. At larger Ra there is less heat-transfer enhancement, at $\mathrm{Pr}\ensuremath{\lesssim}0.7$ no enhancement all. We suggest that small-Pr behavior due breakdown heat-transfer-enhancing Ekman pumping because...

Abstract Results from direct numerical simulation for three-dimensional Rayleigh–Bénard convection in samples of aspect ratio $\Gamma = 0. 23$ and 1/ 2$ up to Rayleigh number $\mathit{Ra}= 2\ensuremath{\times} 1{0}^{12} $ are presented. The broad range Prandtl numbers $0. 5\lt \mathit{Pr}\lt 10$ is considered. In contrast some experiments, we do not see any increase $\mathit{Nu}/ {\mathit{Ra}}^{1/ 3} with increasing $\mathit{Ra}$ , neither due an $\mathit{Pr}$ nor constant heat flux boundary...

This work focuses on the direct numerical simulation of pulsatile flow through a bileaflet mechanical heart valve under physiological conditions and in realistic aortic root geometry. The motion leaflets has been computed from forces exerted by fluid structure both being considered as single dynamical system. To this purpose immersed boundary method, combined with fluid–structure interaction algorithm, shown to be an inexpensive accurate technique for such complex flows. Several complete...

The possible transition to the so-called ultimate regime, wherein both bulk and boundary layers are turbulent, has been an outstanding issue in thermal convection, since seminal work by Kraichnan [Phys. Fluids 5, 1374 (1962)]. Yet, when this takes place how local flow induces it is not fully understood. Here, performing two-dimensional simulations of Rayleigh-B\'enard turbulence covering six decades Rayleigh number Ra up $1{0}^{14}$ for Prandtl $\mathrm{Pr}=1$, first time numerical we find...

Direct numerical simulations of highly turbulent Rayleigh-B\'enard convection up to Rayleigh numbers Ra = ${10}^{9}$ in horizontally periodic domains with aspect ratios \ensuremath{\Gamma} 128, find superstructures very large-scale and long living coherent structures.

In thermal convection, roughness is often used as a means to enhance heat transport, expressed in Nusselt number. Yet there no consensus on whether the vs Rayleigh number scaling exponent (Nu∼Ra^{β}) increases or remains unchanged. Here we numerically investigate turbulent Rayleigh-Bénard convection over rough plates two dimensions, up Ra≈10^{12}. Varying height and wavelength of elements with 200 combinations, reveal existence universal regimes. first regime, local effective can reach 1/2....

We numerically simulate turbulent Taylor-Couette flow for independently rotating inner and outer cylinders, focusing on the analogy with Rayleigh-B\'enard flow. Reynolds numbers of $Re_i=8\cdot10^3$ $Re_o=\pm4\cdot10^3$ respectively, are reached, corresponding to Taylor Ta up $10^8$. Effective scaling laws torque other system responses found. Recent experiments Twente ($T^3C$) setup a similar facility in Maryland at very high have revealed an optimum transport certain non-zero rotation rate...

We study turbulent flows in a smooth straight pipe of circular cross--section up to $Re_{\tau} \approx 6000$ using direct--numerical-simulation (DNS) the Navier--Stokes equations. The DNS results highlight systematic deviations from Prandtl friction law, amounting about $2\%$, which would extrapolate $4\%$ at extreme Reynolds numbers. Data fitting coefficient yields an estimated von K\'arm\'an constant $k 0.387$, nicely fits mean velocity profile, and supports universality canonical...

Recent findings suggest that wall-bounded turbulent flow can take different statistically stationary states, with transport properties, even for the very same values of control parameters. What state system takes depends on initial conditions. Here we analyze multiple states in large-aspect ratio ($\Gamma$) two-dimensional Rayleigh--B\'enard no-slip plates and horizontally periodic boundary conditions as model system. We determine number $n$ convection rolls, their mean aspect ratios...

Ambient conditions surrounding respiratory droplets determine their growth or shrinkage. In cold and humid weather, the can grow due to supersaturation of vapor puff. This phenomenon be explained by our model.

While the heat transfer and flow dynamics in a cylindrical Rayleigh-Bénard (RB) cell are rather independent of aspect ratio Γ (diameter/height) for large Γ, small-Γ considerably stabilizes thus affects transfer. Here, we first theoretically numerically show that critical Rayleigh number onset convection at given follows Ra_{c,Γ}∼Ra_{c,∞}(1+CΓ^{-2})^{2}, with C≲1.49 Oberbeck-Boussinesq (OB) conditions. We then that, broad range (1/32)≤Γ≤32, rescaling Ra→Ra_{ℓ}≡Ra[Γ^{2}/(C+Γ^{2})]^{3/2}...

Abstract The recruitment of patients for rare or complex cardiovascular diseases is a bottleneck clinical trials and digital twins the human heart have recently been proposed as viable alternative. In this paper we present an unprecedented computer model which, relying on latest GPU-acceleration technologies, replicates full multi-physics dynamics within few hours per heartbeat. This opens way to extensive simulation campaigns study response synthetic cohorts disorders, novel prosthetic...

We numerically study the melting process of a solid layer heated from below such that liquid melt develops underneath. The objective is to quantitatively describe and understand emerging topography structures (characterized by amplitude wavelength), which evolve out an initially smooth surface. By performing both two-dimensional (achieving Rayleigh number up $Ra=10^{11}$ ) three-dimensional $Ra=10^9$ direct numerical simulations with advanced finite difference solver coupled phase-field...