Fluid Mechanics with Analysis Using Computations and Experiments
- Aerodynamic Modeling of Wind Turbines
- Bio-inspired Boundary Layer Control
- Dynamic pressure and strain aerodynamic testing using luminescent coatings
- Internal Combustion Engine Flows
- Laser Diagnostics of Oxy-combustion Flames
- Measurements of reacting fuel sprays using high speed imaging
- Morphing Blades for Wind Energy Conversion
- Numerical Study of Acoustic Cavity and Sonic Boom Mitigation using Counter-Flowing Jets
- Rainbow Schlieren Deflectometry
- Rockets are Hard!
Aerodynamic Modeling of Wind Turbines
Wind energy has seen drastic increase in research and installment globally in the last decade. Th enthusiasm in this renewable, green energy source is driven by the increase of energy cost and people’s concern in pollution caused by traditional energy sources in coal and nuclear power-plants. One challenge in wind energy is that the predicted power output of wind turbine has seen large degradation, sometimes more than 30%. Part of the cause lies in the uncertainties in modeling the complex aerodynamics of wind turbines, the interference between turbine and turbine, atmosphere and turbine, and atmosphere and terrain. This research is to apply Computational Fluid Dynamics (CFD) tools in modeling aerodynamics of wind turbines and its wakes. The objective is to develop a high-fidelity computer modeling tool in supporting wind turbine design.
REU Participant’s Role: The student will participate in building and testing the required libraries of the CFD tool on a high performance Linux Workstation. The student will conduct literature search to identify proper test cases for validation purpose, and may involve in developing the test models and carrying out the correlation study.
Bio-inspired Boundary Layer Control
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
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
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.
Laser Diagnostics of Oxy-combustion Flames
Description: Oxy-combustion techniques eliminate the emission of greenhouse gas CO2 into atmosphere and explore alternative uses of CO2. The challenge is to achieve oxy-combustion with minimum energy penalty due to oxygen extraction from air. New technologies studied for oxy-combustion include pure O2/CO2 combustion with fuels, Chemical Looping Combustion (CLC) and Ion Transport Membrane (ITM) combustion. The oxy-combustion flames behave completely different from air-fuel combustion due to the reactive presence of CO2. The goal is to study oxy-combustion flames in a burner to be assembled, using advanced laser diagnostics techniques.
REU Participant’s Role: The student will participate in setup of metal structures for setting up high speed cameras, spectrometer etc for study of oxy-combustion flame in a “plug flow” counter flow burner to be designed and using laser diagnostic techniques. CFD will be used to optimize the counter flow burner exit velocities to a “plug flow” profile. Raman scattering and OH PLIF will be used to study the oxy-combustion flame.
Measurements of reacting fuel sprays using high speed imaging
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.
Morphing Blades for Wind Energy Conversion
Faculty Advisor: Dr. David MacPhee
Description: Many engineering devices are designed to operate optimally at a specific set of conditions, termed the “design point.” As an unfortunate side effect of this design practice, wind turbine efficiency can drop drastically in varying wind loads, especially when speeds fall outside the operational envelope. This project involves flexible blade design for wind turbines, wherein the blade acts as a passive pitch control mechanism, effectively adjusting its geometry in response to varying loading. This adaptability has proven to offer two major advantages over rigid blade designs: 1) higher efficiency, especially away from the design point and 2) an increased operational envelope, allowing for greater energy capture especially in locations experiencing high wind variance.
REU Participant’s Role: The student will utilize computational techniques to help design an optimized wind turbine blade that incorporates flexibility into the design process. Students will gain desirable skills in computational techniques and programming applicable to a vast array of engineering problems in the process.
Numerical Study of Acoustic Cavity and Sonic Boom Mitigation using Counter-Flowing Jets
Flow generated noise, in addition to causing serious human discomfort (e.g. noise from aircraft engines, and sonic boom from the shock wave), can also interact with structures around it causing damage to them (stores and electronic equipment in aircraft weapon bays). By nature of its importance, along with availability of computational resources, flow generated noise has spawned a whole new area of research called computational aeroacoustics (CAA). However, CAA is still in its novice stage because it requires the employed numerical scheme to have very low numerical dissipation and dispersion for resolving delicate acoustic waves, while have enough numerical dissipation to capture shock waves if present. Given the complication in formulating such a scheme, many researchers have resorted to using indirect methods where in the computation of the flow is decoupled from the computation of the sound. However, this approach is less accurate because of its decoupled nature. Lately, advances have been made in the area of computing sound directly along with its flow source, by solving the compressible Navier-Stokes equations. Though some successes have been claimed, the numerical accuracy and computational efficiency of CAA has remained an on-going research topic. Prof. Gary Cheng, a faculty member of the Department of the Aerospace Engineering and Mechanics at UA, has been collaborating with NASA researchers to develop an innovative numerical methodology, a Space-Time Conservation Element Solution Element (CESE) method, for solving conservation laws without using empirical artificial numerical damping. His particular interests in CAA and unsteady aerodynamics are (1) the shear-driven acoustic cavity (such as sunroof of automobiles and aircraft weapon bays), (2) sonic boom from shock systems around supersonic and hypersonic vehicles and its mitigation using counter-flowing jets, and (3) shock-vortices-boundary layer interactions.
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.
Rockets are Hard!
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.