Petrol vapor emissions are the main source of pollution for&nbsp;both standard and hybrid vehicles. It is mainly generated by&nbsp;gasoline evaporation from the fuel tank of both running and&nbsp;parked vehicles; it is mostly driven by fuel temperature variation&nbsp;due to daily temperature changes (if parked) and heat from&nbsp;engine (if running). To prevent its dispersion in the environment,&nbsp;the vapor generated in the fuel tank is usually stored in a carbon&nbsp;canister filter that must be periodically “purged” in order to prevent&nbsp;its saturation, by venting it to the intake manifold. Canister&nbsp;management, made by the Engine Control Unit (ECU), becomes&nbsp;even more critical for hybrid-electric vehicles because thermal&nbsp;engine is often off, thus purging cannot take place. A pressurized&nbsp;fuel tank is often used for hybrid applications, to further isolate&nbsp;vapor from environment, making the fuel system even more&nbsp;complex to model. System design optimization is usually based&nbsp;on experience and experimental correlations, which require time&nbsp;and cost. Thus, comes the need for a comprehensive predictive&nbsp;model useful for both vehicle components (fuel tank and carbon&nbsp;canister) and ECU software design. 
A 0D Matlab®model is proposed, which is able to predict&nbsp;vapor generation from an arbitrary tank in standard and arbitrary 
thermal cycles, with arbitrary tank capacity, geometry&nbsp;and construction and at different filling levels. It is based on a&nbsp;system of thermo-fluid-dynamic differential equations and semiempirical&nbsp;correlations that is iteratively solved in time. Model&nbsp;calibration has been performed by using a small size test tank&nbsp;and validation has been completed on full size tanks for both&nbsp;standard and hybrid-electric applications. The main driving&nbsp;force for vapor generation has been shown to be the amount of&nbsp;empty volume on top of the tank; other significant effects come&nbsp;from tank volume, material, external surface as well as fuel properties.&nbsp;On-going work is to develop and integrate a carbon canister&nbsp;loading/purging model, with the aim to build a full model of&nbsp;the vapor system.

0D Modeling of Fuel Tank for Vapor Generation

Water hammer being the scientist interest since 120 years. In that times the great works of Frizell, Joukovsky, Allievi or Gibson were published. Since then many works were written about this phenomenon, but in none of them, the full analytical solution were presented of a set of partial differential equations (continuity equation and the equation of motion) describing this type of flow. This study compares analytical models of water hammer (quasi-steady solutions as Rich and Jović one, as well as solutions taking into account frequency-dependent friction: Holmboe, Muto-Takahashi and Mei-Jing) with the results simulated with the help of the in-house water hammer modeling program based on the method of characteristics. Mei-Jing's solution has been revised to include the impact of line packing. For all analytical models, formulas for wall shear stress were determined and compared with the results of numerical simulations. Additionally, the usability of the newly developed analytical water hammer solution for the flow accelerating from rest was tested. This type of solution was not known before. Selected inverse Laplace transformations of complex functions appearing in a complete analytical solution, which may allow for the development of a complete analytical solution in the future, will also be presented and discussed.

Progress in Analytical Modeling of Water Hammer

Hydraulic turbines are now subjected to operating points different from the design point. The flow field inside the draft tube of a Francis turbine depends on the operating point. At off-design operations, flow instabilities such as vortex breakdown, reverse flows, and stagnant regions are observed. These flow instabilities are detrimental to the turbine life and also result in hydraulic losses and pressure pulsations in the draft. The study of turbine flow field can be helpful in devising measure which may help to alleviate the effects of these flow instabilities.The present work shows the numerical flow field investigations by employing a vortex identification algorithm. The algorithm works by analyzing the local velocity gradients in the flow field. The algorithm helps in the identification of the local vortex center, shear layers, and pure rotational zones. The analysis has been performed at various locations in the draft tube by extracting the velocity fields at different time steps of the simulation.&nbsp;The analysis has been performed on two operating regions of interest. The first operating point involves a fully developed rotating vortex rope (RVR) in the draft tube which precesses at a frequency of 0.28 times of the runner rotation. This vortical structure is responsible for severe pressure pulsations and involves a shear layer between the stagnant region and the main flow. The present algorithm is able to identify those regions along with an eccentric local rotation center.&nbsp;The second operating regime shows characteristics of deep part load with central solid body rotation in the draft tube flow field. The results show highly swirling flows with very low axial velocity. The flow is confined primarily near the walls. The analysis shows that the extent of the stagnation region at deep part load is more and no inner shear layer is present as compared to the other part-load operations.

Flow Field Investigation in Draft Tube of Francis Turbine at Off-Design Operation Using a Vortex Identification Algorithm

The parachute is widely used in aerospace engineering due to its high performance as a kind of &nbsp;&nbsp;decelerator dragged by aerodynamic forces. The aerodynamic forces acting on the parachute suspension lines and uninflated canopy during the parachute deployment play a key role in the parachute pre-inflation/inflation &nbsp;behavior. The parachute deployment is the first step for parachute to begin decelerating. As one of design conditions the deploy direction should be parallel to the wind direction. In case the deployment direction is not aligned with the relative wind, the phenomenon of line sail can be observed, the line sail gets its name from resemblance of the line curvature to that of sail. In this case the lines and canopy tend to move away from the vehicle faster than the bag and exit the bag from the side or the back. Once the line sail appears there is a tendency for bull whipping, false venting or unsymmetrical inflation to cause high localized stresses in the canopy. These characteristics are undesirable and should be minimized or at least well understood. Moreover, the line sail would result in significant changes in the time sequence to bag strip and therefore the ability to predict conditions at parachute inflation. The entry vehicle attitude is influenced by the direction of the inelastic line load during this time period, and therefore its rate response to the parachute opening load is significantly altered.&nbsp;A numerical model is developed to study the effects of aerodynamics on line sail during the bag stripping process. The model consists of breaking the suspension lines and canopy into several point masses, each acted upon by the aerodynamic drag of a line segment. The point masses are elastically coupled in chain-like fashion between the deployment bag and the vehicle, both of which are modeled in 6 degree-of-freedom. By tracking the line masses relative to the vehicle, the extent of line sail at any time can be presented to check its progress. In addition, the direction of inelastic line loads is accounted for in both vehicle and bag dynamics. The model is helpful in exposing system problems early in the development phase and therefore contributes to minimizing parachute development costs.&nbsp;This work is to numerically simulate the dynamic parachute deploying process. As the result, the effects of aerodynamics on line sail during the process are investigated. Several key parameters are considered such as parachute ejection velocity, angle of attack of spacecraft, Mach number and air density.

Effects of Aerodynamics on Line Sail During Parachute Deployment

The parachute deceleration has an irreplaceable role in aeronautic and astronautic engineering. Its typical applications are in spacecraft recovery, fighter plane pilots for lifesaving, aircraft landing and airdrop. Compared with experiments, numerical simulations can offer significant advantages of expense and turn-around time for parachute design and analysis.During the deployment and subsequent inflation, parachute fabric materials can undergo large and arbitrary deformation in a very short time with sustaining a small stress and strain. such kind of thin and flexible membrane–rope structure poses unavoidable challenges for all of computational structure dynamics (CSD), computational fluid dynamics (CFD) and computational mesh dynamics (CMD).Due to inherent poor accuracy of empirical techniques some computational methods have been developed to predict the dynamic deployment and subsequent inflation. At the early stage the flow around parachute is often treated as incompressible, pressure-based approaches are used for CFD, CMD approaches include spring-analog method, solid elasticity analog method, immersed boundary method and the front tracking method. Recently numerical simulations were conducted on some practical parachute configurations, in which the finite element method was employed to solve both the structure and fluid dynamic leading to the space–time fluid structure interaction (FSI) technique. On the other hand, commercial software LS-DYNA provided some new features to simulate parachute deployment and subsequent inflation, which is based on the coupled &nbsp;arbitrary Lagrangian-Eulerian (ALE) method and penalty algorithm.&nbsp;In this paper, a new numerical FSI simulation technique is proposed and developed to simulate a highly folded parachute configuration by combining the advantages of the nonlinear finite element method and the preconditioning finite volume method. Applying an incompressible fluid solver to study parachute FSI problems has been investigated by many researchers, but the application of a density-based method has been poorly investigated, and the combination of an implicit structure algorithm and an implicit fluid scheme also needs to be developed. Based on these purposes, the code is consisted of three independent modules which are designed to solve the unique problem according to their own strengths. The first module is CSD and an implicit nonlinear structural dynamic module which is based on membrane–rope elements. Different from commercial software, a tangent stiffness matrix for fabric materials has been introduced and derived in detail to formulate the nonlinear implicit structural dynamic equatio

Fluid-Structure Interaction Simulations of Parachute Deployment and Inflation

In the present energy scenario, hydropower accounts for about one-sixth of energy generation worldwide. Apart from being a clean, renewable, and highly efficient energy source, modern hydraulic turbines are supposed to provide grid stability. They are subjected to less efficient operating conditions far from their design point or best efficiency point (BEP). This off-design operation may lead to flow instabilities such as vortices, stagnant regions, or flow reversals in the draft tube.Francis turbines are singly regulated turbines and have fixed pitch blades. They are worst affected by changes in operating point. At part-load (PL) operation, a spiral rotating vortex rope (RVR) develops in the draft tube cone due to swirling flow at the runner exit. This RVR rotates in the direction of runner rotation and has a precession frequency in the range of 0.2-0.4 times the rotational frequency of the runner. The formation of RVR is accompanied by severe pressure pulsations, power swings, fatigue damage, and torque fluctuations in the turbine unit. These detrimental effects may lead to runner failure in extreme cases.Over the years, researchers proposed different methodologies to either mitigate the vortex rope or to reduce its adverse effects for broadening the turbine operating range. Air and water injection in the draft tube are two such methods. The main advantage of these methods is that they may be varied with the variation of turbine operating point. Air injection in the draft tube is one of the most widely used and effective methods to reduce the pressure fluctuations in the draft tube. It leads to the damping of low-frequency pressure pulsations and affects the water flow topology by softening the central core of the RVR. The water jet injection was reported to increase the momentum in the central region and to suppress the pressure fluctuations associated with the RVR. However, water injection was only studied on simplified test rigs, and its implementation in prototypes requires further investigations.The present work reports the numerical simulations performed to compares the effect of axial air and water injections on the flow field in a Francis turbine unit at PL operation. A small turbine test rig is under erection at IIT Roorkee, India, with the aim to study the flow field characteristics during RVR formation and air/water injection methods to mitigate it. The work presents the simulation results of this turbine unit at the part-load operation at which a fully developed RVR is estimated. The simulations have been performed using commercial software ANSYS CFX. The results compare the effect of fluid injections on the pressure pulsations in the draft tube and their influence on the turbine operation.

Comparison of Axial Water and Air Injections in the Draft Tube of a Francis Turbine for RVR Mitigation

Arctic oil spills are particularly detrimental as they could potentially cause extensive ice melting in addition to the overall environmental pollutions they create. A large-scale spill in the Arctic waters, similar to the Deepwater Horizon spill in 2012, could trigger ice sheet deterioration and negatively impact climate cycles globally. Floating oil slicks amongst ice floes absorb ambient energy, i.e., sunlight or energy sources created by cleanup operations such as in situ burning, and transfer that energy to the ice to aggravate melting in thaw season. However, no studies have been undertaken to reveal how oil-ice interaction impacts ice melting. In particular, melting caused by an adjacent immiscible liquid layer and heat transfer to ice in such a condition is not well understood, and basic temperature and velocity field measurements are required to understand the heat transfer mechanisms. This research employs a newly developed simultaneous temperature and velocity field measurement technique to investigate the heat transfer pathways from an oil slick to ice. Temperature measurements are performed by developing a dual-luminescent imaging technique. Two luminescent probes in dual-luminescent imaging have different luminescent characteristics: one probe outputs the temperature-dependent luminescent intensity, another probe outputs the temperature-independent luminescent intensity. Luminescent peaks of the two probes should lie at different wavelengths so that each luminescent output can be acquired by different color images of a high-speed color camera. By taking a ratio of the different color images, spatiotemporal temperature information of oil will be extracted. One challenge in terms of the measurement technique is the dynamic motion of ice as it is melting. The ice-melting moves the geometric position of the ice, especially the interface between the ice-oil. Because of this dynamic motion, dual-luminescent imaging, which is able to capture temperature information over moving objects, is chosen as a unique diagnostic tool. Determining luminescent probes to extract the spatiotemporal temperature of the oil is one of the essential requirements to establish this imaging system. Toluene is selected to represent the spilled fuel, which is immiscible in water as most hydrocarbon petroleum fuels are. The europium-based and pyrene-based luminophore is dissolved into Toluene to result in to be dual-luminescent oil. Seeding particles were also added to Toluene to capture the velocity field of the liquid-phase using particle tracking velocimetry (PTV) technique. A combination of the two techniques for Toluene in a side cooled cavity is performed to capture temperature and velocity field information, respectively. The side cooled cavity simply imitates the ice-oil interface except for the ice melting, which later will be added to future experiments. In the cavity, temperature differences between the cooled side and the oil drive a flow, making a v

Dual-Luminescence Imaging and Particle Tracking Velocimetry for Simultaneous Temperature and Velocity Field Measurements in Hydrocarbons Liquid

The aero-physics of space vehicles entering into atmosphere with orbital and super-orbital velocities is classified as aerothermodynamics which is based on thermally and chemically non-equilibrium gas dynamic models. Development of computational models and tools for description of aerothermodynamics of re-entry into earth atmosphere space vehicles or entry probes has been attempted in the past, as the result some codes have been developed and employed in both scientific and engineering sections. Nowadays numerical simulation of such flows is an integral part in the design process of reentry vehicles. The simulation of weakly ionized gases over reentry vehicles has been performed successfully for a large number of spacecraft, including RAM-C, FIRE, Apollo Command Module, Huygens and Mars Science Laboratory. Computational aerothermodynamics is being routinely used in aerospace community.One of the most important parameters for design is the heat transfer to the spacecraft, which is one of the most difficult to accurately calculate. The heat transfer is mainly composed of two parts: convective and radiative heating. For the stagnation point of a blunt body, the convective heat transfer is roughly proportional to ρ0.5u3.0/RN 0.5 where ρ is the freestream density, u is the freestream speed and RN is the nose radius. The radiative heat transfer is roughly proportional to ρ1.6u8.5RN. The convective heating is usually the largest component, but the previous expressions show that the radiative heating component becomes increasingly important as the size of the spacecraft grows. Because of the increased diameter of modern spacecrafts, there is a lot of interest in the radiative heating component. The FIRE-II flight experiment from the 1960’s is still one of the best set of data available for radiative and total heating measurements. It is commonly used as a validation test case for aerothermodynamics codes.In one of these validation studies, it was observed that two independent NASA codes, DPLR10 (developed at NASA Ames) and LAURA (developed at NASA Langley), showed good agreement for computed convective heating rates with the difference staying below 7% for 11-species air model simulations. That work also showed larger differences in the computed radiative heating rate, on the order of 17 to 25 %. The physical and numerical modeling used in these codes is complex and it is not known which model may be the cause for such differences. A sensitivity analysis may be performed to obtain information on the impact of modeling choices on the results and to explain the differences.This work takes place in the aerothermodynamic analysis of a reentry space vehicle with coupled radiation. The computational method

Computational Study on Radiative Aerothermodynamics of a Reentry Space Vehicle

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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