Since most flows of technological interest are turbulent,
the primary focus of the research in the fluid dynamics
laboratory has as its focus to gain an understanding of
turbulent flows. Often the focus is to gain a better
understanding of how mixing takes place in turbulent flows
so that combustion efficiency can be increased or NOx
emissions reduced. We are also interested in gaining a
better understanding of heat transfer in turbulent flows so
that the heat transfer process can be made more efficient
and can be more accurately predicted. As a third example, we
are starting a study of the two way coupling between
particles and turbulent flow to understand the interaction
of the two phases. In general the problems that are studied
in the laboratory tend to be more fundamental than applied.
though some do have obvious applications.
Since the flows are turbulent, time resolved measurements
are required. Thus, we generally have the challenge of
measuring time resolved quantities of interest such as
velocity, temperature and concentration with spatial
resolution to small scales. Typical frequencies of interest
may run as high as 10kHz with spatial scales as small as 0.1
mm. In order to obtain these measurements, hot wire
anemometers, Laser Doppler Velocimeters, Laser Rayleigh
systems, and cold wire temperature sensors are used. The
output from these systems are digitized using an Analogue to
Digital converter. Analysis is typically accomplished using
386 and 486 computer systems and appropriate software. In
some cases where there are no appropriate sensors for a
specific measurement we develop sensors.
The following contains a brief review of some of the on
going research. If you would like more information on any of
the areas and research opportunities, please feel free to
- * Effect of strain on turbulent flow and heat
- The imposition of strain caused by placing an object
in a turbulent flow can have unexpected effects on the
statistical and structural properties of the turbulence.
For example, when the size of the large scale turbulence
structure is less than the characteristic length of the
object, the turbulence intensity can increase by as much
as 40%. In contrast, if the size of the large scale
structure is significantly larger than the characteristic
length of the object, the turbulence intensity decreases.
Similar strain induced changes are found in the turbulent
axial heat flux. In contrast, the magnitude of the
temperature fluctuations is virtually unchanged though
the turbulent heat flux can be modified by a factor of
two or more.
- The quantification of these effects is of importance
in devices where high temperature turbulent gas flow
comes in contact with surfaces. One example of
technological interest is the heat transfer to turbine
blades in a gas turbine engine.
- * Augmented heat exchange
- Tubes with many, small, spiral flutes on the surface
are found to have heat transfer rates that are as much as
100% larger than the rates in a smooth tube with the same
mean diameter. The pressure drop is similar to that found
in a smooth tube with the same mean diameter. Heat
transfer rates from spiral fluted tubes in cross-flow
have also been found to have higher heat transfer rates
than smooth tubes with the same mean diameter. For spiral
fluted tubes in cross flow, preliminary results indicate
that, at lower Reynolds numbers, the drag is increased
relative to that of a smooth tube while, at higher
Reynolds numbers, the drag is reduced. In this study we
are trying to determine the flow that is responsible for
the augmentation and optimize the geometry to further
improve the augmentation.
- * Particle dispersion in turbulent flows
- Dispersion of solid or liquid particles in turbulent
flows is of both fundamental and technological interest
and, on a more personal level, to people who have hay
fever and related sensitivities. At low volume fractions,
(<10-6), the particles have negligible impact on the
turbulence. This means that the particle dispersion
depends on the turbulence but, because there are so few
particles, the particles have insignificant influence on
the flow. This has been termed one-way coupling. At
higher volume fractions, from 10-6 to 10-3, the number of
particles is large enough that momentum transfer from the
particles has a significant effect on the turbulent flow.
This momentum transfer is highly non-linear and is termed
two-way coupling. The purpose of this study is to use
sophisticated laser diagnostics to quantify the two way
coupling in fundamental flow such as isotropic grid
generated flow and simple shear flows...
- This is a collaborative effort with Professor S. E.
Elghobashi. As such, it will have a strong numerical
component to complement and extend the experimental
- * Effect of free-stream turbulence on jet
- Mixing of an axisymmetric jet with a coflowing stream
is of technological interest as the flow is similar to
that found in many burners. In addition, studies in this
type of flow can be used to understand and better predict
the mixing and dilution of jet engine exhaust in the
atmosphere. In the former case, increased mixing can lead
to increased combustion efficiency and reduced NOx
emissions. The goal of this study is to determine the
effect of free-stream turbulence on the mixing and
development of the jet flow.
- This work is an extension of work performed under NSF
sponsorship in collaboration with Professor G. S.
- * Similarity in plane wake flows
- One of the few analytical predictions in turbulent
flows for thin free shear layers is that the flow should
be similar. Classic studies have supported the
applicability of similarity theory to shear flows but
more recent measurements have show that universal
similarity may not be applicable. One assessment that has
not been performed is to study a cross-over flow which
undergoes a transition from a jet type similarity flow to
a wake type flow. This study is being performed in a
two-dimensional jet in a coflowing stream.
- * Near surface measurements
- Measurement of the time-resolved velocity in the
sublayer and the shear stress at a solid surface are of
interest in both separating and non-separating flows.
However, even in non-separating, laboratory, boundary
layer flow, measurements in the sublayer are challenging.
In this study, we are working on the development of a
laser holographic sensor system for the measurement of
velocity and shear stress.
- This research is carried out in a joint program with
Drs. James Trollinger and James Miller of MetroLaser with
- * Olfactory evoked potentials
- The goal of this applied research is to develop
olfactory evoked potentials for clinical use as objective
measures of olfactory function in the study of sensory
and neurological diseases. Critical to this study is
control of the stimulus. The stimulus is a mixture of an
odurant, water vapor and a carrier that is generally air.
The challenges in this study are (1) to develop a means
to uniformly mix the gas streams so as to obtain a
preselected concentration of water vapor, odurant, and
carrier gas for delivery to a canula that is inserted in
the noise and (2) to develop a model for the study of
flow in the nasal cavity.
This research represents a joint program between Drs.
James Evans and Arnold Starr of the Department of
Neurology. The initial mixing experiments will be
performed in the laboratories of the Mechanical and
Aerospace Engineering Department and the clinical trials
will be performed in the laboratories of the Department