Computational Flow Physics Lab






Research Projects

1. Fluid dynamics and fluid-structure interaction in biological flying and swimming

Flying and swimming animals, such as insects and fish, typically possesses superb maneuverability in locomotion. Their flexible propulsors, i.e., wings and fins, interact with the surrounding fluid in a complicated manner that allows them to move efficiently. Using primarily the computational approach, we model the fluid dynamics and the fluid-structure interaction of these elastic propulsors to understand the fundamental principles of force production and power consumption. In addition, we aim to decipher the role wing/fin deformation in the efficiency and maneuverability of the locomotion. We are capable of solving three-dimensional viscous unsteady flows and their interaction with complicated elastic structures. The research results may provide useful information for developing bio-mimetic aerial and underwater vehicles.

Here is a video presentation of our research on aerodynamics and aeroelasticity of some wings in nature (file size: 32M. Please wait patiently)

Acknowledgements: The sound track in the video is from Louie Schwartzberg’s TED talk: The hidden beauty of pollination; the hummingbird clip in the beginning is from the PBS video: Hummingbird – Magic in the Air; the bee movie is from; the butterfly picture in the end was by Mariko.

Some other videos

Hummingbird flight (13 MB)

Fish swimming (2 MB)

3D simulation of the flow/structure interaction of an elastic rectangular plunging/pitching plate (7 MB)

Fluid-structure interaction of a flexible dragonfly fore-wing (6 MB)

2. Computational modeling of glottal airflow and vocal fold vibration

Voice production process, or phonation, involves aerodynamic interaction of a turbulent glottal jet flow (Re_J=3000) and a pair of three-dimensional vocal folds stretched between the laryngeal cartilages. The pulsatile airflow is responsible for activating and sustaining the vocal fold vibration, and the oscillation pattern of the vocal folds in turn modulates the airflow. The dynamic interaction determines various voice characteristics (e.g., modal voice, breathiness, creakiness, and falsetto). Statistics show that approximately 7.5 million people in the United States have a type of voice disorder. These disorders are debilitating and can lead to discomfort, pain, poor work performance, social withdrawal, and even long-term disability. An advanced computational model of the flow-structure interaction (FSI) during phonation will find extremely useful applications in the medical research, diagnosis, and treatment of these disorders. For fundamental medical research, the stresses and strains in the tissue calculated from the model can be used to correlate with the changes observed in epithelial morphology, tissue permeability, and inflammatory gene expression, and will thus lead to new explanations for the cause of acute phonotrauma. For clinical diagnosis, including the nonlinear tissue properties allows the researchers to model a wide range of vocal fold dynamics including large deformations and abnormal vibrations, and the computational modeling can be combined with high-speed laryngoscopic imaging techniques to analyze the vibratory patterns of the vocal folds and determine the specific disease. For clinical treatment, the computational modeling of phonation can be used to predict and improve the outcome of implants (e.g., medialization thyroplasty), surgically altered larynges (e.g., injection laryngoplasty), engineered vocal fold tissues, and artificial larynges. For these applications, a high-fidelity simulation tool is needed to accurately account for the 3D fluid/tissue dynamics. Based on our previous work, we will: (1) develop an accurate and versatile computational approach suitable for a wide range of biomedical flow-structure interaction problems by combining a 3D immersed-boundary method for incompressible flows and a 3D finite-element (FE) method for large deformations of soft tissues; (2) model and quantify the essential 3D characteristics of the glottal flow and the flow-induced vocal fold vibration; (3) study the effect of the geometry of the larynx on the flow and vocal fold vibration; (4) study the effect of the material properties of the tissue on the flow and vocal fold vibration. These objectives will provide a fundamental building block and also useful guidelines for the final development of a clinically useful tool.

Flow-induced vocal fold vibration. Left: highly unsteady and asymmetric glottal airflow (avi animation, 4 MB); right: vocal fold vibration (gif animation, 4 MB). Click on each image to see the animation.
3D simulation (86 MB)

3. Multiphase flows in complex geometries

Multiphase flows involving two fluids and surface tension arise in a variety of natural and industrial processes, for example, industry processing, pipeline transport, microfluid devices. We have developed an immersed-boundary method to simulate two-phase flows in complex geometries, which can handle arbitrary shape of the solid surface as well as geometrical/topological changes of the fluid-fluid interfaces.

Breakup of the core-annular flow due to the capillary instability (gif animation, 5 MB )

Drops passing through an asymmetric channel. Mixing inside the drops is significantly enhanced.

4. Particle motions in microfluidic channels

The lab-on-a-chip devices have become an exciting research area over the last decade. With integrated microfluidic channels of widths ranging between 1 and 100 µm, the devices can perform specialized functions such as clinical diagnosis, DNA scanning, electrophoretic separation, micro-reaction, cancer cell detection, and bacteria/virus identification. Precise manipulation of particles or cells in the network of microchannels is the key to the performance of the lab-on-a-chip. For example, in cell separation, electrophoresis is used to separate the abnormal cells from a sample fluid containing also the normal cells. To design microfluidic chips for such a process and control the separation with high accuracy and throughput, we need to understand in detail how particles or cells move in electrokinetic flows. We are currently using efficient numerical tools based on the boundary element method (BEM) to investigate the boundary effect on particle motions in electrokinetic flows.

Disturbance of the electric potential caused by a charged particle near an infinite wall.

Our research is supported by the following grants:

CAREER: flapping in the wind - passive mechanisms in insect wings for flight stabilization. Sponsor: National Science Foundation (NSF), 2010-2015.
Collaborative Research: Three-Dimensional Flow-Structure Interaction During Phonation. Sponsor: National Science Foundation (NSF), 2011-2014.
Molecular pathophysiology of acute phonotrauma. Sponsor: NIH/NIDCD, 2010-2015. (PI: Dr. Bernard Rousseau of VUMC).
Vanderbilt Discovery Grant: A high-fidelity computational tool for the laryngeal dynamics during phonation. Sponsor: Vanderbilt University, 2011-2013.
Doctoral New Investigator (DNI): three-dimensional fragmentation of core-annular flow. Sponsor: American Chemical Society / Petroleum Research Fund, 2009-2012.