Fluid Mechanics with Analysis Using Computations and Experiments
- Aerodynamic Modeling of Wind Turbines
- Bio-inspired Boundary Layer Control
- Internal Combustion Engine Flows
- Morphing Blades for Wind Energy Conversion
- Numerical Study of Acoustic Cavity and Sonic Boom Mitigation using Counter-Flowing Jets
- Physiological Fluid Shear Stress and Cancer Stem Cells
- Rainbow Schlieren Deflectometry
- Rapid Prototyping of Aircraft Aerodynamics
- Rapidly-prototyped, highly-flexible, low-Re wings
- 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.
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.
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.
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.
Rapid Prototyping of Aircraft Aerodynamics
The goal of this project is to evaluate computational fluid dynamics (CFD) methodologies for rapid aerodynamic analysis of aircraft and aerodynamic systems. Modern high performance computing allows for the computational simulation of fluid flow to augment traditional wind-tunnel experiments. One of the challenging and more expensive necessities of CFD involves the interaction between the human generated vehicle geometry, the core CFD numerical algorithm, and the resulting solution visualizations. In this summer project, simplified prototypes of CFD tools will be developed and evaluated for future use in a high-performance computing environment.
REU Participant’s Role: The participant will work in a university research team developing, evaluating, and using CFD. The ability to work interactively and quickly in a group is required. Intensive use and understanding of numerical methods and mathematics is necessary. Programming knowledge is strongly encouraged. The participant is expected to write and present a formal paper regarding the research.
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.
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.