Projects – Research Experience for Undergraduates

Fluid Mechanics with Analysis Using Computations and Experiments

Bio-inspired Boundary Layer Control

Faculty Advisor: Dr. Amy Lang, Associate Professor, Aerospace Engineering and Mechanics

This research involves gaining inspiration from nature to control boundary layer flow. The two primary projects involve inspiration from sharks and butterflies. Sharks have movable scales on key locations of their body. These micro-roughness elements are hypothesized (and have been shown using real shark skin sample testing in our water tunnel) to be a passive, flow-actuated separation control mechanism. Butterflies, on the other hand, have a roof-shingle pattern of scales (each 0.1 mm in size) that alter the surface drag over the wing depending on flow orientation. Recent flight testing of live Monarchs has shown an on average 40% decrease in joules/flap when the scales are removed from their wings.

REU participants Role: In both cases experiments will be conducted to simplify a complex flow problem and isolate the potential mechanisms leading to engineering flow control applications. The student will be involved in various phases of building and testing rapid-prototyped bio-inspired models and may use DPIV (Digital Particle Image Velocimetry) to measure flow fields.

Dynamic pressure and strain aerodynamic testing using luminescent coatings

Faculty Advisor: Dr. Paul Hubner, Associate Professor, Aerospace Engineering and Mechanics

Description: Validation of unsteady computational models that simulate fluid-structure interaction of dynamic flight systems (e.g., highly flexible aircraft) requires high-resolution measurement devices. Advanced measurement techniques that acquire distributions of pressure, temperature, and strain on aerodynamic surfaces using non-intrusive detection techniques are of great value as they offer superior spatial resolution and minimally interfere with the flow. The goal of this project is the use of two optical sensors that provide distributed measurements of unsteady loads (pressure) and strain on aerodynamic surfaces. These measurement techniques, fast pressure-sensitive paint (fast PSP) and luminescent photoelastic coatings (LPC), employ optical sensors to provide high spatial resolution distributions of pressure and strain on model surfaces with a bandwidth up to several kHz. While both techniques employ high-powered LEDs, fast-framing cameras, and luminescent coatings, there are challenges to overcome due to the fundamental differences in the response mechanisms.

REU Participants’ Role: Students involved in this project will use scientific equipment to monitor the response of luminescent coatings in including high-powered LEDs, fast-framing digital cameras, and appropriate optics. Software programming and image analysis will be performed. Tests on vibrating specimens will be performed in the lab and in the wind tunnel. Each 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 APS meeting.

Internal Combustion Engine Flows

Faculty Advisor: Dr. Paul Puzinauskas, Associate Professor, Mechanical Engineering

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.

Measurements of reacting fuel sprays using high speed imaging

Faculty Mentor: Dr. Joshua Bittle, Mechanical Engineering

Diesel and gasoline direct injection engines operate with fuel injected directly into the cylinder mere milliseconds prior to ignition in the case of a diesel engine. To enable rapid mixing the fuel is injected at extremely high pressure (~35,000 psi) through nearly invisible holes (<0.1mm). This high pressure, small diameter nozzle creates a finely atomized spray that is able to quickly mix and vaporize in the hot gases in the engine cylinder prior to ignition. To study the spray isolated from the actual engine a constant pressure flow vessel is used with optical grade windows on the sides of the chamber. This allows lighting and camera access to capture high speed (50,000 fps) videos of the sprays to study the penetration speed (>200 mph), spreading angle, liquid and vapor regions, fuel mixture fraction, and other combustion properties throughout the spray. The test chamber is capable of ambient conditions up to of 50 atm and 800°C to study sprays at conditions similar to those near piston top dead center (minimum volume, maximum pressure and temperature) when a typical diesel engine would inject.

REU Participant’s Role: The participant will work with a team of graduate and undergraduate students to perform tests on the using the experimental systems. They will be trained in the system operation, but also the diagnostics including the use of advanced high-speed cameras. The primary experiments are done to support the development and validation of models for numerically predicting the mixture composition at various ambient conditions. There is significant opportunity for data analysis and programming (using Matlab) to develop algorithms for extracting measurements from the spray videos.

Mystery of Turbulence

Faculty Advisor: Dr. Denis Aslangil, Assistant Professor, Aerospace Engineering and Mechanics

This project is motivated by the need to understanding the effects of compressible turbulent mixing observed in hypersonic and supersonic transportation, fusion energy technologies and astrophysical flows. The students’ responsibilities will be performing in-house turbulent flow simulator, postprocessing and saving the generated data, and working with the PhD students in the group to increase our understanding on the compressible turbulent mixing and resolve some mysteries of turbulent flows under extreme conditions. High-fidelity simulations with more than 100 million node points will be performed on the University of Alabama High Performance Computers and NSF machines. Students will be encouraged to attend international conferences, present their work, and publish their findings, in addition to their participation in the APS DFD 2024 Meeting. The project may also include intelligent modeling of turbulent mixing and exploration of machine learning accelerated numerical simulation strategies for compressible flows depending on the participating students’ interests.

REU Participants’ Role: REU students will explore the effects of variation in the material properties on the compressible turbulent mixing. They will work with PhD students and perform high-fidelity high-resolution numerical simulations of turbulent flows on UA and NSF super computers. The project may be paired with theoretical work and physics informed machine learning modeling depending on the students’ strengths and aspirations.

Rainbow Schlieren Deflectometry

Faculty Advisor: Dr. Ajay Agrawal, Professor, Mechanical Engineering

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.

Rockets are Hard!

Faculty Mentor: Dr. Richard Branam, Aerospace Engineering and Mechanics

Current liquid rocket engine cycles face many fluid dynamics challenges in accomplishing their intended purpose, spaceflight. The Dual Expander Cycle Rocket Engine performs its duties by absorbing significant amounts of energy from the combustion process into the propellants. This absorption process is also designed to cool the inner wall of the combustion chamber. The amount of energy is directly related to the thrust level achievable and the survivability of the engine. Current engines use the rocket fuel (liquid hydrogen, RP1, hydrazine, etc.) as the coolant. The Dual Expander will use both the fuel and the oxidizer (liquid oxygen) to cool the engine and then to power the turbopumps used to pump the propellants. Current engines are also built to ease of manufacturing. With employing current casting and machining techniques, several flow path anomalies are introduced; increased pressure loss (efficiency loss), dynamic structural loads (failure modes), combustion chamber cooling limits. This project will employ additive manufacturing design techniques to eliminate such anomalies and improve the overall system performance. Specific focus will be placed on minimizing cooling channel pressure losses, elimination of dynamic structural loads and maximizing the cooling capability of both the fuel and oxidizer flows.

Once the propellants have cooled the combustion chamber walls, they are injected into the combustion chamber. Typically injection designs have been proven over the years using empirical techniques. Design tools are needed to consider new designs for injector geometry for this dual expander cycle. The injectors will be designed and optimized for supercritical fuel and oxider at both maximum operation as well as deep throttling.

The research effort will first employ computational models to optimize critical design parameters and then build subscale models. The models will be water-flow tested to validate the computational model results.

Thermofluidic analysis of multiphase fluid flows in microgeometries

Faculty Advisor: Dr. Hyun Jin Kim, Assistant Professor, Mechanical Engineering

This project will focus on achieving a mechanistic understanding of the heat and mass transfer in complex geometric structures of various length scales. They are found in many thermal transport devices such as plate heat exchangers and microchannel heat sinks. It is difficult to accurately predict their thermal-hydraulic performances with existing knowledge on flow morphology and related transport mechanisms. Heat transfer mechanisms change according to the flow regimes, which is influenced by the channel size and geometry, as well as the thermophysical properties and mass flux of the working fluid. A good understanding of transport characteristics in devices with different geometries and operating conditions is critical for diversifying thermal system portfolios. This project will pursue creative solutions for tough challenges found in HVAC&R (heating, ventilation, air conditioning, & refrigeration), electronics thermal management, energy systems, and environmental conservation.

REU Participants’ Role: REU students with PhD graduate student mentors will conduct thermal-hydraulic measurements, including simultaneous high-speed flow visualization and nonintrusive infrared thermometry to reveal the prevailing flow regimes and their contribution to the thermal transport in various systems. Students will build creative experimental setups to resolve the flow fields inside various complex geometries and illuminate detailed multiphase thermo-fluid operations. Students will also create representational CAD models and use computational fluid dynamics tools for verification and validation.