Fluid Mechanics with Analysis Using Computations and Experiments
- Boundary Layer Control
- High-Speed Imaging of Fuel Sprays
- Internal Combustion Engine Flows
- Magnetic Fluids/Cancer
- Physiological Fluid Shear Stress and Cancer Stem Cells
- Rainbow Schlieren Deflectometry
- Rapidly-prototyped, highly-flexible, low-Re wings
Boundary Layer Control
This research is primarily interested in 2D patterned surfaces with micro-cavities where vortices embedded within the cavities of the microgeometry lead to the formation of a partial slip condition thus favorably increasing the momentum in the boundary layer close to the surface. Dr. Lang is investigating the biomimetic microgeometry of butterfly scales. The flow over the scales, about 100 microns in length, is very low Reynolds number. We can scale up the geometry to ~1 cm and work in high viscosity oil.
REU Participant’s Role: The student will be involved in various phases of building and testing 2D and 3D microgeometry models. The student will use the newly built Couette Flow Facility to measure the drag at low Reynolds number over rectangular embedded cavities. The effect of cavity aspect ratio on the vortex formation and drag reduction will be investigated.
Learn more: Watch a video about a former research project under the direction of Dr. Amy Lang.
High-Speed Imaging of Fuel Sprays
Description: Increasingly, engines and power-generation systems are employing spray-based methods to introduce fuel into the combustion chamber. Sprays and spray combustion involve both physical processes (e.g., fuel vaporization, fuel-air mixing) and chemical processes (e.g., ignition, pollutant formation), neither of which are fully understood. The purpose of this research is to investigate the physical processes involved in fuel sprays, particularly for conditions where fuel is sprayed into relatively low-temperature and low-density surroundings. These conditions are characteristic of advanced engine combustion strategies, such as early direct-injection, which are increasingly being used to enhance efficiency and decrease harmful emissions. Research is conducted in a spray chamber designed with extensive optical access, and through which an inert gas flows continuously during experiments to allow fundamental studies of spray physics in the absence of the complicating effects of combustion. Experimental results could lead to development of improved and more-flexible models that are likely to challenge conventional wisdom about fuel sprays.
REU Participant’s Role: Students will use high-speed imaging techniques to characterize penetration, dispersion, and turbulence of both the liquid and vapor phases of fuel sprays. Students also may be involved in development of novel imaging and diagnostic techniques to probe properties of sprays that have not been previously characterized.
Internal Combustion Engine Flows
This project will use steady flow testing to characterize intake flow configuration effects on in-cylinder flow structures. This will be done with a combination of bulk angular momentum measurements and PIV analysis. A subsequent portion of the investigation will characterize how these structures develop in an unsteady engine using CFD and quantify how they affect engine performance through dynamometer testing. The bulk angular momentum will be measured using an impulse swirl meter as shown in the figure. Such measurements give a good indication of the overall strength of the mean motion in a particular direction, but can be misleading when counter rotating structures are present. Such structure pairs have the potential to be significant turbulence producers, but their counter-rotating orientation can cancel much of their individual momentum when measured in total. The PIV measurements will be made to identify if such a condition exists and also should be able to guide potential intake modifications to enhance the desired in-cylinder flow structures.
REU Participant’s Role: The student will execute the steady bulk flow and PIV analysis with interaction from a graduate student. Several base intake configurations will be tested for swirling or tumbling flow and these base configurations will be refined based on the results generated by the student and through feedback from the CFD and engine testing efforts.
Magnetic fluids, whereby iron oxide nanoparticles are dispersed in aqueous solutions, have potential for localizing various therapies in the human body. When magnetic nanoparticle solutions are injected into the blood stream, they can be trapped through external application of a static magnetic field. By combining the magnetic nanoparticles with a polymer shell to encapsulate a drug, medication can be preferentially released in a narrow region of the body, with a static magnet used to concentrate the drug carriers, and localized hyperthermia treatment induced by a radio frequency magnetic field. By concentrating particles for therapy using magnetics, the effective therapeutic dose per patient can be minimized. The influence of system parameters, particularly dispersion quality and coatings to minimize opsonization by proteins are critical for success. Our laboratory is particularly interested in the development of novel therapeutics that target and destroy cancer cells.
REU Participant’s Role: Students working on this project will be involved with an established cross-disciplinary research team and will conduct both experimental as well as calculation/modeling work. In particular, REU students will use spectroscopy to determine the localization of nanoparticles in simulated blood vessels. Data collected will contribute to the development of mathematical models to better understand the relationship between magnetic nanoparticle size and composition, fluid dynamics, and thermal diffusion.
Physiological Fluid Shear Stress and Cancer Stem Cells
Description: This project aims to provide a fundamental molecular understanding of how cancer stem cells respond and survive in varying physiological fluid shear stresses. In physiological conditions, fluid shear stress on cells occurs through two types of flow: interstitial flow (i.e. fluid flow within the extracellular matrix that surrounds individual cells in a tissue) and vascular flow in blood vessels (e.g., blood cells and circulating tumor cells within blood flow). It is estimated that the former generates shear stresses of ~0.1 dyn/cm2, while the latter generates shear stresses up to 30 dyn/cm2. Vascular blood flow has a large range of shear stresses because of the varying sizes of blood vessel diameters that exist in the body. While some studies have explored the effects of varying shear stress on cellular behavior, many have not considered how the shear stress influences the intracellular molecular events. This is especially true of cancer stem cells, which are believed to be culprits behind cancer metastasis.
REU Participant’s Role: Students working on this project will be involved in multidisciplinary research team versed in both cancer cell biology and in engineering. The students will help develop a microfluidic flow system to study cancer stem cells experiencing interstitial flow and vascular flow. Furthermore, they will be responsible for growing and maintaining cancer stem cells, characterize their stem cell markers using flow cytometry, and characterize their intercellular molecular events using various molecular biology tools. Data generated by the students will contribute to understanding the relationship of fluid dynamics and other external biophysical cues to biological response of the cancer stem cells.
Rainbow Schlieren Deflectometry
In recent years, quantitative Rainbow Schlieren Deflectometry (RSD) technique has been developed and applied to non-intrusively obtain temperature and species concentration measurements in non-reacting and reacting flow configurations. In the RSD technique, the knife-edge of a convection Schlieren system is substituted with a computer generated color filter to relate the angular ray deflection to color (or hue) in the rainbow Schlieren image. The figure shows a RSD image of a laminar flame. Unique features of the RSD technique are: no lasers are involved and, hence, the apparatus is relatively inexpensive; the technique is robust and it can accept minor mechanical vibrations and misalignments; the measurements are obtained across the whole field; and high spatial resolution (on the order of 0.1 mm) and temporal resolution (on the order of 5000 Hz) can be attained in systems with field of view of 100 mm or more. Recently, we have developed a miniature RSD apparatus using the principles of the macro-scale rainbow Schlieren apparatus.
REU Participant’s Role: The students will be involved in applying the RSD technique to study phenomena such as near injector flow of a fuel atomizer, two-phase flow inside micro-channels, turbulent structure of flames, shock-cell structures of under-expanded jets, temperature in heated jets and flames.
Rapidly-prototyped, highly-flexible, low-Re wings
Description: Micro air vehicles (MAVs) because of their small size (< 15 cm) and relatively low flight speeds (U ~ 10 m/s) experience low Reynolds number (< 100,000) flow, drastically changing the resulting flow field and integrated forces compared to conventional people-carrying aircraft. As such, researchers study and employ biologically-inspired designs with highly flexible structures that have the ability to passively control wing shape to improve stability, alleviate gust divergence and increase aerodynamic efficiency. A common phenomenon of low-Re membrane wings is the flow-induced, large-amplitude vibration of the membrane. This vibration is substantially larger for free trailing-edge geometries compared to perimeter constrained geometries, enabling greater interaction with the flow. At pre-stall angles of attack, the vibration frequency scales with the aeroelastic and applied strain of the membrane as well as the cell size. Because of the vibration, and not simply the time-averaged shape of the deformation, aerodynamic parameters such as lift and efficiency can be improved. In the proposed investigation, instead of generically-shaped, rigid (metal) frames, 3D printed frames of various thickness, porosity and shape (e.g. more biologically realistic) will be tested to assess the effect of frame flexibility on aerodynamic characteristics, structural integrity and potentially energy harvesting capability by employing piezoelectric membranes.
REU Participants’ Role: The summer participants will perform force, flow-field, deformation, stress and power measurements over rapidly-prototyped, flexible, wing geometries to assess the extent the flexibility affects both aerodynamic characteristics and energy extraction. They will assist in model design and fabrication, test configuration, image acquisition and data post processing. Instead of working solo, each REU student will work collaboratively with other students in Dr. Hubner’s research group. The student will be expected to present their research results at the fall fluid mechanics APS meeting.