Browsing by Author "Yu, Huidan (Whitney)"
Now showing 1 - 10 of 15
Results Per Page
Sort Options
Item Coupled thermal-fluid analysis with flowpath-cavity interaction in a gas turbine engine(2013-12) Fitzpatrick, John Nathan; Wasfy, Tamer; Nalim, M. Razi; Yu, Huidan (Whitney); Anwar, SohelThis study seeks to improve the understanding of inlet conditions of a large rotor-stator cavity in a turbofan engine, often referred to as the drive cone cavity (DCC). The inlet flow is better understood through a higher fidelity computational fluid dynamics (CFD) modeling of the inlet to the cavity, and a coupled finite element (FE) thermal to CFD fluid analysis of the cavity in order to accurately predict engine component temperatures. Accurately predicting temperature distribution in the cavity is important because temperatures directly affect the material properties including Young's modulus, yield strength, fatigue strength, creep properties. All of these properties directly affect the life of critical engine components. In addition, temperatures cause thermal expansion which changes clearances and in turn affects engine efficiency. The DCC is fed from the last stage of the high pressure compressor. One of its primary functions is to purge the air over the rotor wall to prevent it from overheating. Aero-thermal conditions within the DCC cavity are particularly challenging to predict due to the complex air flow and high heat transfer in the rotating component. Thus, in order to accurately predict metal temperatures a two-way coupled CFD-FE analysis is needed. Historically, when the cavity airflow is modeled for engine design purposes, the inlet condition has been over-simplified for the CFD analysis which impacts the results, particularly in the region around the compressor disc rim. The inlet is typically simplified by circumferentially averaging the velocity field at the inlet to the cavity which removes the effect of pressure wakes from the upstream rotor blades. The way in which these non-axisymmetric flow characteristics affect metal temperatures is not well understood. In addition, a constant air temperature scaled from a previous analysis is used as the simplified cavity inlet air temperature. Therefore, the objectives of this study are: (a) model the DCC cavity with a more physically representative inlet condition while coupling the solid thermal analysis and compressible air flow analysis that includes the fluid velocity, pressure, and temperature fields; (b) run a coupled analysis whose boundary conditions come from computational models, rather than thermocouple data; (c) validate the model using available experimental data; and (d) based on the validation, determine if the model can be used to predict air inlet and metal temperatures for new engine geometries. Verification with experimental results showed that the coupled analysis with the 3D no-bolt CFD model with predictive boundary conditions, over-predicted the HP6 offtake temperature by 16k. The maximum error was an over-prediction of 50k while the average error was 17k. The predictive model with 3D bolts also predicted cavity temperatures with an average error of 17k. For the two CFD models with predicted boundary conditions, the case without bolts performed better than the case with bolts. This is due to the flow errors caused by placing stationary bolts in a rotating reference frame. Therefore it is recommended that this type of analysis only be attempted for drive cone cavities with no bolts or shielded bolts.Item Experimental Investigation of Pressure Development and Flame Characteristics in a Pre-Combustion Chamber(2024-08) Miller, Jared; Nalim, Mohamed Razi; Larriba-Andaluz, Carlos; Yu, Huidan (Whitney)This study contributes to research involving wave rotor combustors by studying the development of a hot jet issuing from a cylindrical pre-combustion chamber. The pre-chamber was developed to provide a hot fuel-air mixture as an ignition source to a rectangular combustion chamber, which models the properties of a wave rotor channel. The pre-combustion chamber in this study was rebuilt for study and placed in a new housing so that buoyancy effects could be studied in tandem with other characteristics. The effectiveness of this hot jet is estimated by using devices and instrumentation to measure properties inside the pre-chamber under many different conditions. The properties tracked in this study include maximum pressure, the pressure and time at which an aluminum diaphragm ruptures, and the moment a developed flame reaches a precise location within the chamber. The pressure is tracked through use of a high-frequency pressure transducer, the diaphragm rupture moment is captured with a high-speed video camera, and the flame within the pre-chamber is detected by a custom-built ionization probe. The experimental apparatus was used in three configurations to study any potential buoyancy effects and utilized three different gaseous fuels, including a 50%-50% methane-hydrogen blend, pure methane, and pure hydrogen. Additionally, the equivalence ratio within the pre-chamber was varied from values of 0.9 to 1.2, and the initial pressure was set to either 1.0, 1.5, or 1.75 atm. In all cases, combustion was initiated from a spark plug, causing a flame to develop until the diaphragm breaks, releasing a hot jet of fuel and air from the nozzle inserted into the pre-chamber. In the pressure transducer tests, it was found that hydrogen produced the highest pressures and fastest rupture times, and methane produced the lowest pressures and slowest rupture times. The methane-hydrogen blend provided a middle ground between the two pure fuels. An equivalence ratio of 1.1 consistently provided the highest pressure values and fastest rupture out of all tested values. It was also found that the orientation has a noticeable impact on both the pressure development and rupture moment as higher maximum pressures were achieved when the chamber was laid flat in the “vertical jet” orientation as compared to when it was stood upright in the “horizontal jet” orientation. Additionally, increasing the initial pressure strongly increased the maximum developed pressure but had minimal impact on the rupture moment. The tests done with the ion probe demonstrated that an equivalence ratio of 1.1 produces a flame that reaches the ion probe faster than an equivalence ratio of 1.0 for the methane-hydrogen blend. In its current form, the ion probe setup has significant limitations and should continue to be developed for future studies. The properties analyzed in this study deepen the understanding of the processes that occur within the pre-chamber and aid in understanding the conditions that may exist in the hot jet produced by it as the nozzle ruptures. The knowledge gained in the study can also be applied to develop models that can predict other parameters that are difficult to physically measure.Item Experimental investigation on traversing hot jet ignition of lean hydrocarbon-air mixtures in a constant volume combustor(2013-12) Chinnathambi, Prasanna; Nalim, M. Razi; Yu, Huidan (Whitney); Zhu, Likun; Anwar, SohelA constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.Item Experimental Measurement of Blood Pressure in 3-D Printed Human Vessels(2022-05) Talamantes, John, Jr.; Yu, Huidan (Whitney); Chen, Jie; Zhu, LikunA pulsatile flow loop can be suitable for measurement of in vitro blood pressure. The pressure data collected from such a system can be used for evaluating stenosis in human arteries, a condition in which the arterial lumen size is reduced. The objective of this work is to develop an experimental system to simulate blood flow in the human arterial system. This system will measure the in vitro hemodynamics using 3-D prints of vessels extracted from patient CT images. Images are segmented and processed to produce 3-D prints of vessel geometry, which are mounted in the loop. Control of flow and pressure is made possible by the use of components such as a pulsatile heart pump, resistance, and compliance elements. Output data is evaluated by comparison with CFD and invasive measurement. The system is capable of measurement of the pressures such as proximal, Pa, and distal, Pd, pressures to evaluate in vivo conditions and to assess the severity of stenosis. This is determined by use of parameters such as fractional flow reserve (FFR=Pd/Pa) or trans-stenotic pressure gradient (TSPG=Pa-Pd). This can be done on a non-invasive, patient specific basis, to avoid the risk and high cost of invasive measurement. In its operation, the preliminary measurement of blood pressures demonstrates agreement with the invasive measurement as well as the CFD results. These preliminary results are encouraging and can be improved upon by continuing development of the experimental system. A working pulsatile loop has been reached, an initial step taken for continued development. This loop is capable of measuring the flow and pressure from in a 3-D printed artery. Future works will include more life-like material for the artery prints, as well as cadaver vessels.Item Fully parallelized Lattice Boltzmann scheme for fast extraction of biomedical geometry(Elsevier, 2019-06) Wang, Zhiqiang; Zhao, Ye; Yu, Huidan (Whitney); Lin, Chen; Sawchuck, Alan P.; Mechanical and Energy Engineering, School of Engineering and TechnologyWe develop a fully parallel numerical method which quickly performs 2D and 3D segmentation on GPU to extract anatomical structures from medical images. The algorithm solves the level set equations completely within a Lattice Boltzmann model (LBM). Compared with existing LBM-based segmentation approaches, a parallel distance field regularization is added to the LBM computing scheme to keep computation stable with large time step iteration. This approach also avoids external regularization which has been a major impediment to direct parallelization of level set evolution with LBM. It allows the whole computing process to be efficiently executed on GPU. Moreover, the method can be incorporated with different image features to adopt in various image segmentation tasks. Therefore, our method enables fully GPU accelerated geometric extraction from medical images, leading to high computing performance which is demanded in many practical applications. This method is used to exactly accurate 2D and 3D anatomical structures from many real world CT and MRI images. The achieved results can also directly feed required boundary information to LBM-based hemodynamics simulation.Item General power-law temporal scaling for unequal-size microbubble coalescence(APS, 2020) Chen, Rou; Yu, Huidan (Whitney); Zeng, Jianhuan; Zhu, Likun; Mechanical and Energy Engineering, School of Engineering and TechnologyWe systematically study the effects of liquid viscosity, liquid density, and surface tension on global microbubble coalescence using lattice Boltzmann simulation. The liquid-gas system is characterized by Ohnesorge number Oh ≡ ηh/√ρhσrF with ηh, ρh, σ, and rF being viscosity and density of liquid, surface tension, and the radius of the larger parent bubble, respectively. This study focuses on the microbubble coalescence without oscillation in an Oh range between 0.5 and 1.0. The global coalescence time is defined as the time period from initially two parent bubbles touching to finally one child bubble when its half-vertical axis reaches above 99% of the bubble radius. Comprehensive graphics processing unit parallelization, convergence check, and validation are carried out to ensure the physical accuracy and computational efficiency. From 138 simulations of 23 cases, we derive and validate a general power-law temporal scaling T ∗ = A0γ−n, that correlates the normalized global coalescence time (T ∗) with size inequality (γ ) of initial parent bubbles. We found that the prefactor A0 is linear to Oh in the full considered Oh range, whereas the power index n is linear to Oh when Oh < 0.66 and remains constant when Oh > 0.66. The physical insights of the coalescence behavior are explored. Such a general temporal scaling of global microbubble coalescence on size inequality may provide useful guidance for the design, development, and optimization of microfluidic systems for various applications.Item Image Segmentation, Parametric Study, and Supervised Surrogate Modeling of Image-based Computational Fluid Dynamics(2022-05) Islam, Md Mahfuzul; Yu, Huidan (Whitney); Du, Xiaoping; Wagner, DianeWith the recent advancement of computation and imaging technology, Image-based computational fluid dynamics (ICFD) has emerged as a great non-invasive capability to study biomedical flows. These modern technologies increase the potential of computation-aided diagnostics and therapeutics in a patient-specific environment. I studied three components of this image-based computational fluid dynamics process in this work. To ensure accurate medical assessment, realistic computational analysis is needed, for which patient-specific image segmentation of the diseased vessel is of paramount importance. In this work, image segmentation of several human arteries, veins, capillaries, and organs was conducted to use them for further hemodynamic simulations. To accomplish these, several open-source and commercial software packages were implemented. This study incorporates a new computational platform, called InVascular, to quantify the 4D velocity field in image-based pulsatile flows using the Volumetric Lattice Boltzmann Method (VLBM). We also conducted several parametric studies on an idealized case of a 3-D pipe with the dimensions of a human renal artery. We investigated the relationship between stenosis severity and Resistive index (RI). We also explored how pulsatile parameters like heart rate or pulsatile pressure gradient affect RI. As the process of ICFD analysis is based on imaging and other hemodynamic data, it is often time-consuming due to the extensive data processing time. For clinicians to make fast medical decisions regarding their patients, we need rapid and accurate ICFD results. To achieve that, we also developed surrogate models to show the potential of supervised machine learning methods in constructing efficient and precise surrogate models for Hagen-Poiseuille and Womersley flows.Item Mechanism of damped oscillation in microbubble coalescence(Elsevier, 2019-04) Chen, Ron; Zeng, Jianhuan; Yu, Huidan (Whitney); Mechanical and Energy Engineering, School of Engineering and TechnologyThis work is part of our continuous research effort to reveal the underlying physics of bubble coalescence in microfluidics through the GPU-accelerated lattice Boltzmann method. We numerically explore the mechanism of damped oscillation in microbubble coalescence characterized by the Ohnesorge (Oh) number. The focus is to address when and how a damped oscillation occurs during a coalescence process. Sixteen cases with a range of Oh numbers from 0.039 to 1.543, varying in liquid viscosity from 0.002 to 0.08kg/(m · s) correspondingly, are systematically studied. First, a criterion of with or without damped oscillation has been established. It is found that a larger Oh enables faster/slower bubble coalescence with/without damped oscillation when (Oh < 0.477)/(Oh > 0.477) and the fastest coalescence falls at Oh ≈ 0.477. Second, the mechanism behind damped oscillation is explored in terms of the competition between driving and resisting forces. When Oh is small in the range of Oh < 0.477, the energy dissipation due to viscous effect is insignificant, sufficient surface energy initiates a strong inertia and overshoots the neck movement. It results in a successive energy transformation between surface energy and kinetic energy of the coalescing bubble. Through an analogy to the conventional damped harmonic oscillator, the saddle-point trajectory over the entire oscillation can be well predicted analytically.Item Mechanisms of axis-switching and saddle-back velocity profile in laminar and turbulent rectangular jets(2013-08) Chen, Nan; Yu, Huidan (Whitney); Nalim, M. Razi; Zhu, Likun; Anwar, SohelWe numerically investigate the underlying physics of two peculiar phenomena, which are axis-switching and saddle-back velocity profile, in both laminar and turbulent rectangular jets using lattice Boltzmann method (LBM). Previously developed computation protocols based on single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann equations are utilized to perform direct numerical simulation (DNS) and large eddy simulation (LES) respectively. In the first study, we systematically study the axis-switching behavior in low aspect-ratio (AR), defined as the ratio of width over height, laminar rectangular jets with AR=1 (square jet), 1.5, 2, 2.5, and 3. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the streamwise velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. The 45° and 90° axis-switching occur in characteristic decay (CD) region consecutively at the early and late stage. The half-width contour (HWC) reveals that 45° axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when 45° axis-switching occurs. The close examinations of flow pattern and vorticity contour, as well as the correlation between streamwise velocity and vorticity, indicate that 90° axis-switching results from boundary effect. Specific flow patterns for 45° and 90° axis-switching reveal the mechanism of the two types of axis-switching respectively. In the second study we develop an algorithm to generate a turbulent velocity field for the boundary condition at jet inlet. The turbulent velocity field satisfies incompressible continuity equation with prescribed energy spectrum in wave space. Application study of the turbulent velocity profile is on two turbulent jets with Re=25900. In the jets with AR=1.5, axis-switching phenomenon driven by the turbulent inlet velocity is more profound and in better agreement with experimental examination over the laminar counterpart. Characteristic jet development driven by both laminar and turbulent inlet velocity profile in square jet (AR=1) is also examined. Overall agreement of selected jet features is good, while quantitative match for the turbulence intensity profiles is yet to be obtained in future study. In the third study, we analyze the saddle-back velocity profile phenomenon in turbulent rectangular jets with AR ranging from 2 to 6 driven by the developed turbulent inlet velocity profiles with different turbulence intensity (I). Saddle-back velocity profile is observed in all jets. It has been noted that the saddle-back's peak velocities are resulted from the local minimum mixing intensity. Peak-center difference &Deltapc and profound saddle-back (PSB) range are defined to quantify the saddle-back level and the effects of AR and I on saddle-back profile. It is found that saddle-back is more profound with larger AR or slimmer rectangular jets, while its relation with I is to be further determined.Item Modeling and design optimization of a microfluidic chip for isolation of rare cells(2013-12) Gannavaram, Spandana; Zhu, Likun; Yu, Huidan (Whitney); Xie, Jian; Anwar, SohelCancer is still among those diseases that prominently contribute to the numerous deaths that are caused each year. But as technology and research is reaching new zeniths in the present times, cure or early detection of cancer is possible. The detection of rare cells can help understand the origin of many diseases. The current study deals with one such technology that is used for the capture or effective separation of these rare cells called Lab-on-a-chip microchip technology. The isolation and capture of rare cells is a problem uniquely suited to microfluidic devices, in which geometries on the cellular length scale can be engineered and a wide range of chemical functionalizations can be implemented. The performance of such devices is primarily affected by the chemical interaction between the cell and the capture surface and the mechanics of cell-surface collision and adhesion. This study focuses on the fundamental adhesion and transport mechanisms in rare cell-capture microdevices, and explores modern device design strategies in a transport context. The biorheology and engineering parameters of cell adhesion are defined; chip geometries are reviewed. Transport at the microscale, cell-wall interactions that result in cell motion across streamlines, is discussed. We have concentrated majorly on the fluid dynamics design of the chip. A simplified description of the device would be to say that the chip is at micro scale. There are posts arranged on the chip such that the arrangement will lead to a higher capture of rare cells. Blood consisting of rare cells will be passed through the chip and the posts will pose as an obstruction so that the interception and capture efficiency of the rare cells increases. The captured cells can be observed by fluorescence microscopy. As compared to previous studies of using solid microposts, we will be incorporating a new concept of cylindrical shell micropost. This type of micropost consists of a solid inner core and the annulus area is covered with a forest of silicon nanopillars. Utilization of such a design helps in increasing the interception and capture efficiency and reducing the hydrodynamic resistance between the cells and the posts. Computational analysis is done for different designs of the posts. Drag on the microposts due to fluid flow has a great significance on the capture efficiency of the chip. Also, the arrangement of the posts is important to contributing to the increase in the interception efficiency. The effects of these parameters on the efficiency in junction with other factors have been studied and quantified. The study is concluded by discussing design strategies with a focus on leveraging the underlying transport phenomena to maximize device performance.