This paper aims to simulate the interaction between a simplified tongue replica with expiratory air flow considering the flow in the pharyngeal airway to be turbulent. A three-dimensional model with a low-Re SST turbulence model is adopted. An Arbitrary Eulerian-Lagrangian description for the fluid governing equation is coupled with the Lagrangian structural solver via a partitioned approach, allowing deformation of the fluid domain to be captured. Both the three-dimensional flow features and collapsibility of the tongue are presented. In addition, examining initial constriction height ranging from 0.8&#x2009;mm to 11.0&#x2009;mm and tongue replica modulus from 1.25&#x2009;MPa to 2.25&#x2009;MPa, the influence of both of these parameters on the flow rate and collapsibility of the tongue is also investigated and discussed. Numerical simulations confirm expected predisposition of apneic patients with narrower airway opening to flow obstruction and suggest much severe tongue collapsibility if the pharyngeal flow regime is turbulent compared to laminar.

M. R. Rasani

K. Inthavong

J. Y. Tu

Simulation of Pharyngeal Airway Interaction with Air Flow Using Low-Re Turbulence Model

This investigation focuses on the application of the computational
fluid dynamics tool FLUENT to the study of flows over the NACA
63&#x2013;415 airfoil at various angles of attack. With the aim of selecting the
most suitable turbulence model to simulate flow around ice-accreted
airfoils, this work concentrates on assessing the prediction capabilities
of various turbulence models on clean airfoils at the large angles
of attack that cause highly separated flows to occur. The study was
undertaken by conducting simulations with the one-equation Spalart-Allmaras (SA) model, the two-equation RNG <svg     style="vertical-align:-0.1638pt;width:21.9375px;" id="M1" height="12.4375" version="1.1" viewBox="0 0 21.9375 12.4375" width="21.9375"  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg">
	
		
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</svg> and SST <svg     style="vertical-align:-0.1638pt;width:25.575001px;" id="M2" height="12.4375" version="1.1" viewBox="0 0 25.575001 12.4375" width="25.575001"  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg">
	
		
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</svg> models, and the Reynolds stress model (RSM). Domain discretization
was carried out using general quadrilateral grids generated with
GAMBIT, the FLUENT preprocessing tool. Comparisons were made
with available experimental data.

Fernando Villalpando

Marcelo Reggio

Adrian Ilinca

Assessment of Turbulence Models for Flow Simulation around a Wind Turbine Airfoil

This paper serves as a summary of our recent work on LES for supersonic MVG. An implicitly implemented large eddy simulation (ILES) by using the fifth-order <i  >WENO</i> scheme is applied to study the flow around the microramp vortex generator (MVG) at Mach 2.5 and <svg     style="vertical-align:-3.3907pt;width:79.400002px;" id="M1" height="15.4" version="1.1" viewBox="0 0 79.400002 15.4" width="79.400002"  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg">
	
		
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</svg>.  A number of new discoveries on the flow around supersonic MVG have been made including spiral points, surface separation topology, source of the momentum deficit, inflection surface, Kelvin-Helmholtz instability, vortex ring generation, ring-shock interaction, 3D recompression shock structure, and influence of MVG decline angles. Most of the new discoveries, which were made in 2009, were confirmed by experiment conducted by the UTA experimental team in 2010.  A new 5-pair-vortex-tube model near the MVG is given based on the ILES observation. The vortex ring-shock interaction is found as the new mechanism of the reduction of the separation zone induced by the shock-boundary layer interaction.

Qin Li

Chaoqun Liu

Implicit LES for Supersonic Microramp Vortex Generator: New Discoveries and New Mechanisms


		Railway is the key transport means in China including the Mainland, Taiwan, and Hong Kong. Consequent to so many big arson and accidental fires in the public transport systems including trains and buses, fire safety in passenger trains is a concern. Numerical simulations with Computational Fluid Dynamics on identified fire scenarios with typical train compartments in China will be reported in this paper. The heat release rate of the first ignited item was taken as the input parameter. The mass lost rate of fuel vapor of other combustibles was estimated to predict the resultant heat release rates by the combustion models in the software. Results on air flow, velocity vectors, temperature distribution, smoke layer height, and smoke spread patterns inside the train compartment were analyzed. The results are useful for working out appropriate fire safety measures for train vehicles and determining the design fire for subway stations and railway tunnels.

W. K. Chow

K. C. Lam 

N. K. Fong

S. S. Li

Y. Gao

Numerical Simulations for a Typical Train Fire in China

Many tall halls of big space volume were built and, to be built in many construction projects in the Far East, particularly Mainland China, Hong Kong, and Taiwan. Smoke is identified to be the key hazard to handle. Consequently, smoke exhaust systems are specified in the fire code in those areas. An update on applying Computational Fluid Dynamics (CFD) in smoke exhaust design will be presented in this paper. Key points to note in CFD simulations on smoke filling due to a fire in a big hall will be discussed. Mathematical aspects concerning of discretization of partial differential equations and algorithms for solving the velocity-pressure linked equations are briefly outlined. Results predicted by CFD with different free boundary conditions are compared with those on room fire tests. Standards on grid size, relaxation factors, convergence criteria, and false diffusion should be set up for numerical experiments with CFD.

C. L. Chow

Simulating Smoke Filling in Big Halls by Computational Fluid Dynamics

In this paper some recent efforts for credible computational fluid dynamics (CFD) simulations in China are reviewed. The most important effort is that, following similar activities in the West such as ECARP and AIAA Drag Prediction Workshops, a series of workshops on credible CFD simulations had been initiated. These workshops were with ambitions to assess the status of CFD in China. Another major effort is an ongoing project to establish a software platform for studying the credibility of CFD solvers and performing credible CFD simulations. The platform, named WiseCFD, was designed to implement a seamless CFD process and to circumvent tedious repeating manual operations. It had also been a powerful job manager for CFD with capabilities to support plug and play (PnP) solver integration as well as distributed or parallel computations. Some future work on WiseCFD was proposed, and also envisioned was how WiseCFD and the European QNET-CFD Knowledge Base can benefit mutually.

Li Li

Bai Wen

Liang Yihua

Recent Efforts for Credible CFD Simulations in China

A computational fluid dynamics (CFDs) method
utilizing unstructured grid technology has been
employed to compute vortical flow around a <svg style="vertical-align:-0.1575pt;width:18.1875px;" id="M1" height="10.075" version="1.1" viewBox="0 0 18.1875 10.075" width="18.1875"  xmlns="http://www.w3.org/2000/svg">
	<g transform="matrix(1.25,0,0,-1.25,0,10.075)">
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			<text transform="matrix(1,0,0,-1,-60.74,68.91)">
				<tspan style="font-size: 7.85px; " x="0" y="0">∘</tspan>
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		</g>
	</g>
</svg>
delta wing with sharp leading edge, which is specially known as the geometry of the second international vortex flow experiment (VFE-2). In
VFE-2, <svg style="vertical-align:-0.1575pt;width:18.1875px;" id="M2" height="10.075" version="1.1" viewBox="0 0 18.1875 10.075" width="18.1875"  xmlns="http://www.w3.org/2000/svg">
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			</text>

			<text transform="matrix(1,0,0,-1,-60.74,68.91)">
				<tspan style="font-size: 7.85px; " x="0" y="0">∘</tspan>
			</text>

		</g>
	</g>
</svg> delta wings with different leading
edges had been broadly investigated by experiments, which resulted in a special database for
CFDs codes validation. The emphasis of this
paper is to investigate the effectiveness of an
adjoint-base grid adaptation method for unstructured grid in capturing concentrated vortices generated at sharp edges or flow separation lines of
lifting surfaces flying at high angles of attack. 
Earlier experiences in vortical flow simulations
had indicated that the vortex behavior is highly
dependent on the local grid resolution both on
body surface and space. The adjoint-based adaptation method used here is hoped to save grid
points with a reasonable grid resolution for vortical flow simulations. The basic idea is to construct a new adaptive sensor in a grid adaptation process with the intent to tell where the elements should be smaller or larger by introducing an adjoint formulation to relate the estimated
functional error to local residual errors of both
the primal and adjoint solutions.

An Initial Investigation of Adjoint-Based Unstructured Grid Adaptation for Vortical Flow Simulations

A 3D dynamic computer model for the movement of the head-neck complex is presented. It incorporates anatomically correct information about the diverse elements forming the system. The skeleton is considered as a set of interconnected rigid 3D bodies following the Newton-Euler laws of movement. The muscles are modeled using Enderle's linear model, which shows equivalent dynamic characteristics to Loeb's virtual muscle model. The soft tissues, namely, the ligaments, intervertebral disks, and facet joints, are modeled considering their physiological roles and dynamics. In contrast with other head and neck models developed for safety research, the model is aimed to study the neural control of the complex during fast eye and head movements, such as saccades and gaze shifts. In particular, the time-optimal hypothesis and the feedback control ones are discussed.

Daniel A. Sierra

John D. Enderle

3D Dynamic Modeling of the Head-Neck Complex for Fast Eye and Head Orientation Movements Research

This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counter-rotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated.

Lin Chen

Ping Lu

New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer

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Modelling and Simulation in Engineering aims to provide a forum for the discussion of formalisms, methodologies and simulation tools which relate to the modelling and simulation of human-centred engineering systems.

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Modelling and Simulation in Engineering