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Flow Separation Control with Static Vortex Generator
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Numerical simulation of subsonic flow over a NACA0012 airfoil with a 6° angle of attack is performed.
The immersed boundary method is utilized to model the vortex generator located at 01C.
The baseline case without the vortex generator and the flow control case with passive vortex generator
are studied. Simulation results show that the vortex generator has reduced the size of separation zone.
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Animation:
Baseline case: Contours of streamwise velocity
Realplayer [550Kb]
Animation:
Flow control case: Contours of streamwise velocity
Realplayer [1.5Mb]
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Flow behind a Pair of Active Vortex Generators
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Numerical simulation of subsonic flow over a flat plate behind a pair of vortex generators.
Immersed boundary method has been used to simulate the active vortex generator (AVG).
The instantaneous flow field reveals the response of flow to the motion of AVG.
The phase-averaged results are in good agreement with experimental results.
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Animation:
Contours of streamwise velocity
Realplayer [156Kb]
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LES of Supersonic Boundary Layer Transition
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The oblique transition process of a flat-plate boundary layer at a free-stream
Mach number of 4.5 and a Reynolds number of 10,000 based on free-stream velocity
and inflow displacement thickness is investigated by large eddy simulation (LES).
A pair of oblique first-mode perturbation is imposed on the inflow boundary. The
Transition process is divided into several stages: the linear and weakly nonlinear
growth of disturbance, the appearance of staggered lamda-vortex pattern, the
evolution of lamda-vortex into hairpin vortex, the break-down of hairpin vortex.
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Animation:
Iso-surface of low pressure and
countours of spanwise vorticity
AVI Video Clip [1.5Mb]
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DNS of Leading Edge Receptivity
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The leading-edge receptivity to the free-stream disturbance is simulated by
direct numerical simulation. Linear growth of Tollmien-Schlichting waves along
the flat-plat is calculated as the test case for code validation. The leading-edge
receptivity of the compressible boundary-layer over the flat plate to the free-stream
acoustic and vortical disturbances is investigated. The generation and distinct
growth of the Tollmien-Schlichting waves are clearly observed along the flat-plate.
Attempt has also been made to simulated the flow with more complex geometry, such
as the modified Joukowsky airfoil. In this case, the instability wave is generated
near the leading edge followed by a rapid decay and then begins to grow in the rear
part of the airfoil.
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DNS of Separated Flow around NACA0012 Airfoil
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Flow separation around an NACA 0012 airfoil at 12° and 20° angles of attack has be
investigated by direct numerical simulation (DNS). Complex flow separation,
vortex shedding, vortex merging, and vortex pairing are observed. The small-scale
vortices associated with the Kelvin-Helmholtz instability are also observed along
the shear layer near the trailing-edge. These phenomena are in good agreement with
the experimental results obtained by Shih, et al. (1992, 1995).
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Animation:
Flow separation around NACA0012 airfoil:
12° angle of attack
AVI Video Clip [1.75MB]
Animation:
Flow separation around NACA0012 airfoil:
20° angle of attack
AVI Video Clip [1.75Mb]
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Numerical Simulation of 3D Separated Flow around a Slender Delta Wing
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The three-dimensional separated flow around a slender flat-plate delta wing with
sharp leading-edge at a 12.5 degree angle of attack has been studied by direct
numerical simulation. At Reynolds number of 1.96 x 105 based on the
chord length and the free-stream velocity, the Kelvin-Helmholtz-type instability
as well as vortex shedding are observed near the leading-edge of the delta wing.
It has been found that the shedding of the small-scale vortical structures originates
not only from the Kelvin-Helmholtz-type instability but also from the separation of
the secondary vortex.
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Numerical Simulation of Flow around Delta Wing
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The flow around a delta wing with round leading-edge is simulated first at zero
angle of attack then at 20 degree angle of attack. a C-H type mesh system for a
halp-plane model of the delta wing is used. The mesh is C-type along the streamwise
direction and H-type in the cross section. An elliptic grid generation method, first
proposed by Spekreijse, is used to generated the 3D grid. Flow separation and strong
streamwise vortex are observed.
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Computational Dynamics of Rigid Bodies
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Multiple Impacts of a Falling Rigid Rod
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A three-dimensional computational dynamics model has been developed to
simulate the multiple impacts of a falling slender rigid rod with the ground. A set of dynamics
equations is solved for six general coordinates of the system. The rigid rod is descritized
using unstructured meshes similar to those in the finite element method.
The ground surface is modeled as a distributed viscoelastic foundation.
A compliant contact model with nonlinear damping is used to calculate the normal
component of impact load and the tangential load.
The total impact contact force is computed as the surface
integration of distributed impact load.
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Animation:
Multiple impacts of a falling rigid rod with the ground
Realplayer [620Kb]
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Multiple Impacts of a Falling Model Cell Phone
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A sequence of multiple impacts of a falling model cell phone with the ground has been simulated by
the three-dimensional computational dynamics model for rigid bodies. The model output includes the
time history of impact forces and total energy, kinetic energy, and potential energy, the pre- and post-impact
velocities at center of mass, the pre- and post-impact angular velocity, impact location and impact angle for
each impact.
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Animation:
Multiple impacts of a falling cell phone with the ground
AVI Video Clip [820Kb]
Realplayer [820Kb]
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Numerical Tumbling Box Test for Model Cell Phone
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A three-dimensional computational dynamics model has been developed to
simulate the tumbling box test for a model cell phone. The numerical tumbling
box test can provide detailed information regarding the distributions of peak
impact contact force, cumulated impact impulse, impact frequency, etc. The numerical
results will help engineers to design the tumbling test properly.
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Animation:
Tumbling of a model cell phone in a rotating box
Realplayer [800Kb]
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Computational Hydraulics and Hydrology
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Numerical Simulation of Flow with Free Surface
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A fully three-dimensional numerical model based on the Navier-Stokes equations
for unsteady incompressible flow has been developed.
The Arbitrary Lagrangian-Eulerian (ALE) representations
of the equations are combined with the moving grid method to solve problems
involving free surfaces. The kinematic condition on the free surface is
explicitly coupled with the governing equations.
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Animation:
Free Surface Flow in a Box
Realplayer [520Kb]
Animation:
Moving Grid Method
Realplayer [320Kb]
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3D Integrated Surface/Groundwater Model for
Loxahatchee River
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The three-dimensional integrated surface/groundwater model has been developed
to study the saltwater intrusion to the Northwest Fork of the Loxahatchee River and Estuary,
under the influence of tide from the Atlantic Ocean and freshwater input at some upstream tributaries.
The model output will be used to estimate the impact of saltwater intrusion to surface and ground water body
and to study the possibility of keeping the salinity below a certain level in order to restore the cypress
tree community at the upstream of the Northwest Fork, which represents one of the largest vestiges of native
cypress river-swamp within southeast Florida
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Animation:
Salinity distribution in Loxhatchee River
Realplayer [620Kb]
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Northern Palm Beach County Regional Model
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The purpose of this project is to develop a hydrologic and hydraulic regional model
using WASH123D for the north Palm Beach County area and study different scenarios
on how to deliver supplemental water to the Northwest Fork of Loxahatchee
River to meet the minimum flow request.
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