Scholarly Works, Mechanical Engineering

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https://hdl.handle.net/10919/23262

Research articles, presentations, and other scholarship

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Development of an OpenFOAM Solver for Hydroacoustic Simulations: An Application for Acoustic Fish Deterrence
George, Edwin; Palmore, John A., Jr.; Alexander, William Nathan; Politano, Marcela; Smith, David; Woodley, Christa (2023-11-20)
DNS of n-heptane droplet vaporization and combustion
Palmore, John A., Jr. (2019-03-27)
This paper presents fully resolved numerical simulations of droplet vaporization and combustion using a finite volume solver. The work was developed to study the influence of droplet vaporization on spray combustion phenomena. The flow solver is designed for simulating turbulent, multiphase flows under the low-Mach assumption. Simulations are performed on a Cartesian grid, and are able to track the freely deforming liquid droplets using a Volume of Fluid method. Transport of momentum and scalars is performed using an algorithm designed for liquid-gas flows with high density ratio. Vaporization is handled automatically based on the local requirements of mass and energy conservation at the interface and the requirement of thermodynamic equilibrium between the two phases. N-Heptane is chosen as the fuel because of its common use a fuel surrogate. Initial results are demonstrated for individual burning droplets in quiescent and uniform flows. These results are compared to classical correlations for the vaporization rate and flame stand off ratio. Finally, droplet-droplet interaction is studied through simulations of co-burning droplets.
Effect of straining flow and droplet shape on vaporization rate of liquid fuel droplet
Setiya, Meha; Palmore, John A., Jr. (2020-11-24)
This study focuses on the effect of planar straining flow on the vaporization of droplets. This work is motivated by spray combustion in gas turbines where the turbulence inside the combustor leads to the presence of both significant flow strain and droplet deformation. While a small amount of literature exists on the effect of droplet deformation on vaporization, there are no systematic investigations of the effect of flow strain on the vaporization of freely-deforming droplets. Recent theoretical studies on ellipsoidal droplets suggest that deformation enhances the vaporization rate. Additionally, our initial studies suggest that flow strain can also impact the vaporization rate. Therefore, a complete understanding of droplet vaporization requires studying the interaction between both droplet deformation and flow strain. This study uses an in-house code for interface-resolved direct numerical simulations of vaporizing multiphase flows. It mimics a freely-deforming droplet falling at its terminal velocity with an imposed strain rate. The influence of the deformation and flow strain on vaporization will be investigated by varying the relevant non-dimensional groups such as the Weber number and the non-dimensional strain rate.
Friction of Extensible Strips: an Extended Shear Lag Model with Experimental Evaluation
Mojdehi, Ahmad R.; Holmes, Douglas P.; Williams, Christopher B.; Long, Timothy E.; Dillard, David A. (2016-02-22)
A gravity update scheme using PID controller for droplet traveling at terminal velocity in air flow
Lin, Yushu; Palmore, John A., Jr. (2021-05-26)
To improve the combustion efficiency in gas turbines, it will be important to find out positions of droplets and the evaporated fuel vapors in the combustion chamber. In our study, we investigate the drag coefficient of droplets, because drag force will affect droplet dynamics. In practice, simple drag correlations are commonly used in DNS, which are single-parameter dependent on Reynolds number. However, if droplets have complex interactions with the flow, more parameters should be taken into consideration. For example, in gas turbine combustion, it is natural to think that deformation, evaporation and internal circulation of droplets have impact on drag coefficient as well. Therefore, drag coefficient will have a dependence on related parameters (effective diameter, Weber number, density ratio, etc.). To reveal the dependence of drag coefficient on probable parameters, we perform simulations of an evaporating droplet traveling at its terminal velocity in high-temperature air by using the numerical framework developed by our research group. This framework uses an interface-capturing DNS for vaporizing multiphase flows. Since the drag force is dynamically changing, an algorithm which updates the gravity to balance the drag force is developed. We incorporate PID controller in our scheme to mimic the difference between gravity and drag force in a more robust manner compared to our previous work [Setiya and Palmore, ESSCI, 2020]. The resultant gravity is then used to characterize the behavior of drag coefficient.
High Stokes Number Droplets in Homogeneous Isotropic Turbulent Flow
Miranda, Cairen J.; Palmore, John A., Jr. (2020-03-11)
Understanding sprays in turbulent flow is important to help improve the performance of gas turbine engines, and can be achieved by simulating liquid droplets in turbulent flow. Introduction of liquid droplets into homogeneous isotropic turbulent (HIT) flow requires forcing of the Navier- Stokes equations to counteract decay caused by energy dissipation. A source term (consisting of a forcing coefficient multiplied with the local velocity field) is added to the momentum equation in order to induce constant turbulent kinetic energy. We will study the effect of such a source in this work. In turbulent flow, vortices within the flow tend to affect the path of the droplet. Stokes number is used in determining these effects on a droplet’s motion. Smaller droplets (St < 0:5) may tend to follow the streamlines however the larger droplets (0:5 < St < 5) are subjected to centrifugal force generated by the turbulent eddies and will be pushed away from the vortex core. However droplets with significantly higher Stokes Number (~ 50) have high inertia and therefore do not deviate significantly in the presence of a vortex. In fact, the droplet response time may be longer than the life of the characteristic turbulent eddy, and as such special care must be exercised to study these types of flows in HIT. In this study, an Eulerian framework is used to solve the gas phase transport equations and Lagrangian equations are used to solve the liquid phase. We study high Stokes Number droplets in HIT using a triply periodic cubic domain. The forcing scheme combines the feedback control approach of Bassenne et. al. [1], with the filtered linear forcing technique of Palmore and Desjardins [2]. We study the effects of HIT forcing algorithm on high Stokes Number droplet sprays in turbulent flow.
L2OrkMote: Reimagining a Low-Cost Wearable Controller for a Live Gesture-Centric Music Performance
Tsoukalas, Kyriakos D.; Kubalak, Joseph R.; Bukvic, Ivica Ico (ACM, 2018-06)
Laptop orchestras create music, although digitally produced, in a collaborative live performance not unlike a traditional orchestra. The recent increase in interest and investment in this style of music creation has paved the way for novel methods for musicians to create and interact with music. To this end, a number of nontraditional instruments have been constructed that enable musicians to control sound production beyond pitch and volume, integrating filtering, musical effects, etc. Wii Remotes (WiiMotes) have seen heavy use in maker communities, including laptop orchestras, for their robust sensor array and low cost. The placement of sensors and the form factor of the device itself are suited for video games, not necessarily live music creation. In this paper, the authors present a new controller design, based on the WiiMote hardware platform, to address usability in gesture-centric music performance. Based on the pilot-study data, the new controller offers unrestricted two-hand gesture production, smaller footprint, and lower muscle strain.
Learning Human Objectives from Sequences of Physical Corrections
Li, Mengxi; Canberk, Alper; Losey, Dylan P.; Sadigh, Dorsa (IEEE, 2021-05-30)
When personal, assistive, and interactive robots make mistakes, humans naturally and intuitively correct those mistakes through physical interaction. In simple situations, one correction is sufficient to convey what the human wants. But when humans are working with multiple robots or the robot is performing an intricate task often the human must make several corrections to fix the robot’s behavior. Prior research assumes each of these physical corrections are independent events, and learns from them one-at-a-time. However, this misses out on crucial information: each of these interactions are interconnected, and may only make sense if viewed together. Alternatively, other work reasons over the final trajectory produced by all of the human’s corrections. But this method must wait until the end of the task to learn from corrections, as opposed to inferring from the corrections in an online fashion. In this paper we formalize an approach for learning from sequences of physical corrections during the current task. To do this we introduce an auxiliary reward that captures the human’s trade-off between making corrections which improve the robot’s immediate reward and long-term performance. We evaluate the resulting algorithm in remote and in-person human-robot experiments, and compare to both independent and final baselines. Our results indicate that users are best able to convey their objective when the robot reasons over their sequence of corrections.
Method to study effect of straining flow on droplet vaporization at low Reynolds number
Setiya, Meha; Palmore, John A., Jr. (2020-03)
Current trends in gas turbine development requires cleaner and efficient combustion. In order to understand the behavior of spray combustion in detail, the numerical study on combustion can give insights about the complete process including fuel injection, droplet breakup, droplet evaporation and its combustion. We use a numerical framework developed by Palmore and Desjardins to simulate this phenomena [1]. This framework uses NGA which is a Direct Numerical Simulation (DNS) code for simulating low-Mach number Navier-Stokes equations. It uses interface-resolved DNS in which dynamics of flow are solved using first principles i.e. conservation of mass, momentum and energy. Matching conditions at the interface of liquid-gas phase ensures the conservation of mass, momentum and energy across the interface. As a result, the deformation of the evaporating droplet, internal flow, boundary layer growth and its separation from the droplet are captured in detail. Although the framework is capable of studying 3D flows fully, this initial study will use 2D simulations to reduce the computation expense. The results of this study will motivate further detailed investigations in 3D in future. The present work involves the method development for inflow boundary condition for single droplet evaporation problem. In addition to this, the paper studies about the effect of planar straining flow on evaporation rate of the fuel droplet. The fuel used for this study is n-Decane.
Pneumatically Balanced Heavy Truck Air Suspensions for Improved Roll Stability
Chen, Yang; Ahmadian, Mehdi; Peterson, Andrew (SAE International, 2015-01-01)
This study provides a simulation evaluation of the effect of maintaining balanced airflow, both statically and dynamically, in heavy truck air suspensions on vehicle roll stability. The model includes a multi-domain evaluation of the truck multi-body dynamics combined with detailed pneumatic dynamics of drive-axle air suspensions. The analysis is performed based on a detailed model of the suspension's pneumatics, from the main reservoir to the airsprings, of a new generation of air suspensions with two leveling valves and air hoses and fittings that are intended to increase the dynamic bandwidth of the pneumatic suspensions. The suspension pneumatics are designed such that they are able to better respond to body motion in real time. Specifically, this study aims to better understand the airflow dynamics and how they couple with the vehicle dynamics. The pneumatic model is coupled with a roll-plane model of the truck to evaluate the effect of the suspension pneumatic dynamics on the body roll, as well as the force transmission to the sprung mass. The results of the study show that maintaining a balanced airflow through the suspension improves the dynamic responsiveness of the suspension to steering, causing less body roll.
Predicting Erosion from Airborne Particles on Surfaces using a Soft-Sphere Collision Model
Miranda, Cairen J.; Palmore, John A., Jr. (American Institute of Aeronautics and Astronautics, 2021-08-02)
In this study, we hypothesize that the soft-sphere collision model has the ability to simulate the erosion that occurs when airborne particles impact a surface. The key insight in this paper is to connect the particle-surface work performed during impact to the amount of erosion on the surface. This can only be done through the introduction of a new collision modeling strategy. This paper borrows the soft-sphere modeling approach from the DEM community, and uses it in a new context to model particle impact and surface erosion. In the aerospace literature, the most commonly used collision approach is the hard-sphere model. Here the trajectories of the particles are determined by momentum-conserving binary collisions characterized by a coefficient of restitution. This model is limited in that it is not capable of predicting the physical interactions that occur simultaneously to particle impact such as surface erosion and any adhesive processes. On the other hand, the soft-sphere model is a physics-based approach which represents the particle as a Kelvin-Voigt material. The approach explicitly resolves the impact by introducing a spring-dashpot force to the governing dynamical equation for particle motion. The spring force is non-zero only when the particle is in contact with the wall. One underexplored consequence of this approach is that it provides a time history of the particle-surface work. This information may be used in turn, to compute the amount of surface erosion. This paper uses the given information to develop a modeling approach that resolves both particle-surface collisions and surface erosion under a single framework. This model is validated using the coefficient of restitution and erosion data of Grant and Tabakoff[1, 2], which was defined for sand particles. The model is then applied to look at particle erosion on a single stage rotor-stator configuration.
Rail Surface Measurement And Multi-Scale Modeling Of Wheel-Rail Contact
Alemi, Mohammad Mehdi; Taheri, Saied; Ahmadian, Mehdi (ASME, 2016-01-01)
In railroad industries, one of the most important concepts is the ability to model and estimate the friction between the rail and the wheels. Overall, creating a general friction model is a challenging task because friction is influenced by different factors such as surface metrology, properties of materials in contact, surface contamination, flash temperature, normal load, sliding velocity, surface deformation, inter-surface adhesion, etc. Moreover, increase in the number of interfering factors in the process would add to the complexity of the friction model. Therefore, reliable prediction of the friction both theoretically and empirically is sensitive to how the model parameters are measured. Due to both safety and energy concerns, any attempts towards a better understanding of wheel/rail contact are considered important for the railroad industry. In this study, surface characteristics of four rail surfaces were measured at 20 microns over a rectangular area using a portable Nanovea Jr25 optical surface profilometer and the results were studied using various statistical procedures and Fractal theory. Furthermore, a 2D rectangular area was measured in this study because 1D height profile doesn’t capture all the necessary statistical properties of the surface. For surface roughness characterization, the 3D parameters such as root-mean-square (RMS) height, skewness, kurtosis and other important parameters were obtained according to ISO 25178 standard. To verify the statistical results and fractal analysis, a British Pendulum Skid Resistance Tester was used to measure the average sliding coefficients of friction based on several experiments over a 5 cm contact length for all four rail sections. The results supported this fact that the rail surface with lower fractal dimension number has the lower friction. In effect, the larger fractal dimension number simply would add more microtexture features to the contact surface which potentially increases the friction. This paper will discuss the results and the next steps towards a better understanding of the friction potential between the wheels and the track.
Simulation Evaluation on the Rollover Propensity of Multi-Trailer Trucks at Roundabouts
Chen, Yang; Zheng, Xiaohan; Peterson, Andrew; Ahmadian, Mehdi (SAE International, 2019-01-01)
The main intent of this study is to provide a simulation analysis of rollover dynamics of multi-trailer commercial vehicles in roundabouts. The results are compared with conventional tractor-semitrailer with a single 53-ft trailer for roundabouts that are of typical configuration to those in the U.S. cities. The multi-trailer commercial vehicles that are considered in this study are the A-double trucks commonly operated in the U.S. roads with the trailer length of 28 ft, 33 ft, and 40 ft. The multi-body dynamic models for analyzing the rollover characteristics of the trucks in roundabouts are established in TruckSim®. The models are intended to be used to assess the maximum rollover indexes of each trailer combination subjected to various circulating speeds for two types of roundabouts, 140-ft single-lane and 180-ft double-lane. The simulation results suggest that the 40-ft double has rollover speed thresholds 2-9 mph lower (more vulnerable to rolling over) as compared with the conventional 53-ft semi-trailer-truck. The lower roll stability for the 40-ft A-train configuration is attributed to its pintle-hitch coupling that allows for a certain amount of roll degree of freedom between the front and rear trailers. In addition, the worse tracking performance of the 40-ft double due to its longer wheelbase contributes to the heavier use of truck apron, greatly increasing the chance of rollover. The results also indicate that the 28-ft and 33-ft double-trailer trucks possess better maneuverability (less off-tracking) and can tolerate the rollover speed 1-3 mph higher than that of the 53-ft single-trailer truck. Furthermore, it is found that increasing the trailer from 28 ft to 33 ft results in the truck slightly less prone to rollover crashes, because of their longer wheelbase providing a slight amount of additional roll stability.
The study of droplet internal circulation and its interaction with droplet deformation
Lin, Yushu; Palmore, John A., Jr. (2023-11-19)
The study of liquid droplet is important for applications like spray-painting, fire suppression, and spray combustion. Droplet morphology has a great impact in these applications, for example, in spray conditions, droplets of various sizes are generated from jet atomization, and the large droplets have strong deformation. The highly deformed droplets have very different characteristics compared to spherical droplets, but many studies on droplet dynamics are based on the spherical droplet assumption. To develop a more accurate modeling of liquid droplet in jet simulations, we use numerical approaches to investigate the mechanism of droplet deformation. Weber number, which measures the balance of surface tension and inertia, is a key non-dimensional group that quantifies droplet deformation. However, droplets with same Weber number do not always have an identical shape. For example, our previous work[Lin and Palmore, 2022] demonstrated that internal circulation also influences droplet shape. Therefore, a deeper understanding in droplet internal circulation is needed. In this work, we will explore a wider range of droplet parameters relevant to a wide array of applications for droplets to study the interaction between droplet internal circulation and deformation.
Towards Use And Reuse Driven Big Data Management
Xie, Zhiwu; Chen, Yinlin; Griffin, Julie; Walters, Tyler; Tarazaga, Pablo Alberto; Kasarda, Mary E. (2015-06-03)
We propose a use and reuse driven big data management approach that fuses the data repository and data processing capabilities in a co-located, public cloud. It answers to the urgent data management needs from the growing number of researchers who don’t fit in the big science/small science dichotomy. This approach will allow researchers to more easily use, manage, and collaborate around big data sets, as well as give librarians the opportunity to work alongside the researchers to preserve and curate data while it is still fresh and being actively used. This also provides the technological foundation to foster a sharing culture more aligned with the open source software development paradigm than the lone-wolf, gift-exchanging small science sharing or the top-down, highly structured big science sharing. To materialize this vision, we provide a system architecture consisting of a scalable digital repository system coupled with the co-located cloud storage and cloud computing, as well as a job scheduler and a deployment management system. Motivated by Virginia Tech’s Goodwin Hall instrumentation project, we implemented and evaluated a prototype. The results show not only sufficient capacities for this particular case, but also near perfect linear storage and data processing scalabilities under moderately high workload.
Validating a numerical framework for resolved simulations of vaporizing droplets
Palmore, John A., Jr.; Desjardins, O. (2018-07-26)
Standard practice when simulating spray combustion is to represent the spray as a collection of droplets which vaporize and subsequently combust. Empirical models are used to approximate the process of droplet vaporization, however, these models were largely developed for isolated droplets in uniform flow. These models also typically neglect the influence of droplet deformation and internal heat transfer on vaporization. The impact of these assumptions on the accuracy of model predictions still needs to be evaluated. One natural way to study this, is the comparison of data from direct numerical simulations with that of spray models. The current work demonstrates a direct numerical simulation framework for simulating vaporizing liquid-gas flows with a focus towards spray combustion. The framework builds from first principles as the governing equations are developed directly from the principles of conservation of mass, momentum, and energy without the introduction of empirical models. A VOF method is used for interface transport, which is coupled with a robust momentum solver for high density ratio flows. Scalar transport is performed using BQUICK for advection and an unconditionally stable monotone scheme for diffusion. Thermodynamic equilibrium at the interface is handled using the Clausius-Clapeyron relation. This initial study focuses on validating the framework against known solutions for single droplet vaporization in simple flows. Numerical simulations in three dimensions are compared to analytical solutions and the accuracy of the framework is verified. Comparisons with experimental correlations for vaporizing droplets in uniform flow indicate a good match between numerical and experimental results.

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