Professor John C. LaRue


Department of Mechanical and Aerospace Engineering, University of California, Irvine

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E-mail: jclarue@uci.edu
Office: EG 3226
Phone: (949) 824-6724

Turbulence Research Laboratory

UCI Microtechnology and Manufacturing Laboratory

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General Information

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 contact me.


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Research Projects

Downstream Decay of a Two-Dimensional Jet-Wake in a Co-flowing Stream

Mixing with a Passive Swirl Generator

The Role of Reactant Unmixedness, Strain Rate and Length Scale on Combustor Performance  (A joint project with UCICL)


An overview

* Effect of strain on turbulent flow and heat transfer
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 measurements.
 
* Effect of free-stream turbulence on jet mixing
 
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. Samuelsen.
 
* 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 AFOSR sponsorship.
 
* 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 of Neurology.
 

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