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Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems
Title
Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems.
Creator
Groves, Curtis, Kassab, Alain, Das, Tuhin, Kauffman, Jeffrey, Moore, Brian, University of Central Florida
Abstract / Description
Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data...
Show moreSpacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data. Quantifying the uncertainty in analytical predictions is imperative to the success of any simulation-based product. The method could provide an alternative to traditional (")validation by test only(") mentality. This method could be extended to other disciplines and has potential to provide uncertainty for any numerical simulation, thus lowering the cost of performing these verifications while increasing the confidence in those predictions.Spacecraft requirements can include a maximum airflow speed to protect delicate instruments during ground processing. Computational Fluid Dynamics can be used to verify these requirements; however, the model must be validated by test data. This research includes the following three objectives and methods. Objective one is develop, model, and perform a Computational Fluid Dynamics analysis of three (3) generic, non-proprietary, environmental control systems and spacecraft configurations. Several commercially available and open source solvers have the capability to model the turbulent, highly three-dimensional, incompressible flow regime. The proposed method uses FLUENT, STARCCM+, and OPENFOAM. Objective two is to perform an uncertainty analysis of the Computational Fluid Dynamics model using the methodology found in (")Comprehensive Approach to Verification and Validation of Computational Fluid Dynamics Simulations("). This method requires three separate grids and solutions, which quantify the error bars around Computational Fluid Dynamics predictions. The method accounts for all uncertainty terms from both numerical and input variables. Objective three is to compile a table of uncertainty parameters that could be used to estimate the error in a Computational Fluid Dynamics model of the Environmental Control System /spacecraft system.Previous studies have looked at the uncertainty in a Computational Fluid Dynamics model for a single output variable at a single point, for example the re-attachment length of a backward facing step. For the flow regime being analyzed (turbulent, three-dimensional, incompressible), the error at a single point can propagate into the solution both via flow physics and numerical methods. Calculating the uncertainty in using Computational Fluid Dynamics to accurately predict airflow speeds around encapsulated spacecraft in is imperative to the success of future missions.
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Date Issued
2014
Identifier
CFE0005174, ucf:50662
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005174
COMPUTATIONAL FLUID DYNAMICS INVESTIGATION OF THE ORIENTATION OF A PEDIATRIC LEFT VENTRICLE ASSIST DEVICE CANNULA TO REDUCE STROKE EVENTS
Title
COMPUTATIONAL FLUID DYNAMICS INVESTIGATION OF THE ORIENTATION OF A PEDIATRIC LEFT VENTRICLE ASSIST DEVICE CANNULA TO REDUCE STROKE EVENTS.
Creator
Guimond, Stephen, Kassab, Alain, University of Central Florida
Abstract / Description
Ventricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta....
Show moreVentricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta. Currently, the implantation angle of the VAD cannula is not taken into consideration. Since the VADs supply a significant amount of blood flow to the aorta, the implantation angle can greatly affect the trajectory of the formed thrombi as well as the cardiac flow field inside of the aortic arch. This study aims to vary the implantation angle of a pediatric Left Ventricle Assist Device (LVAD) through a series of computational fluid dynamics (CFD) software simulations focusing on the aortic arch and its branching arteries of a 20 kg pediatric patient in order to reduce the occurrence of stroke.
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Date Issued
2012
Identifier
CFH0004305, ucf:45044
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0004305
Fluid Dynamics Modeling and Sound Analysis of a Bileaflet Mechanical Heart Valve
Title
Fluid Dynamics Modeling and Sound Analysis of a Bileaflet Mechanical Heart Valve.
Creator
Khalili, Fardin, Mansy, Hansen, Kassab, Alain, Steward, Robert, Zaurin, Ricardo, University of Central Florida
Abstract / Description
Cardiovascular disease (CVD) is one of the main causes of death in the world. Some CVD involve severe heart valve disease that require valve replacement. There are more than 300,000 heart valves implanted worldwide, and about 85,000 heart valve replacements in the US. Approximately half of these valves are mechanical. Artificial valves may dysfunction leading to adverse hemodynamic conditions. Understanding the normal and abnormal valve function is important as it help improve valve designs....
Show moreCardiovascular disease (CVD) is one of the main causes of death in the world. Some CVD involve severe heart valve disease that require valve replacement. There are more than 300,000 heart valves implanted worldwide, and about 85,000 heart valve replacements in the US. Approximately half of these valves are mechanical. Artificial valves may dysfunction leading to adverse hemodynamic conditions. Understanding the normal and abnormal valve function is important as it help improve valve designs. Modeling of heart valve hemodynamics using computational fluid dynamics (CFD) provides a comprehensive analysis of flow, which can potentially help explain clinical observations and support therapeutic decision-making. This detailed information might not be accessible with in-vivo measurements. On the other hand, finite element analysis (FEA), is an efficient way to analyze the interactions of blood flow with blood vessel and tissue layers. In this project both CFD and FEA simulations were performed to investigate the flow-induced sound generation and propagation of sound waves through a tissue-like material. This method is based on mapping the transient pressure (force) fluctuations on the vessel wall and solving for the structural vibrations in the frequency domain. These vibrations would then be detected as sound on the epidermal surface. Advantages of the methods used in the current study include: (a) capability of providing accurate solution with a faster solution time; (b) inclusion of the fluid(-)structure interaction between blood flow and the arterial wall; and (c) accurately capturing some of the spectral features of the velocity fluctuation measured over the epidermal surface.
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Date Issued
2018
Identifier
CFE0007029, ucf:52038
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007029
FUNDAMENTAL UNDERSTANDING OF INTERACTIONS AMONG FLOW, TURBULENCE, AND HEAT TRANSFER IN JET IMPINGEMENT COOLING
Title
FUNDAMENTAL UNDERSTANDING OF INTERACTIONS AMONG FLOW, TURBULENCE, AND HEAT TRANSFER IN JET IMPINGEMENT COOLING.
Creator
Hossain, Md. Jahed, Kapat, Jayanta, Ahmed, Kareem, Gordon, Ali, Wiegand, Rudolf, University of Central Florida
Abstract / Description
The flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on...
Show moreThe flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on three particular geometric configurations (a narrow wall, an array impingement configuration and a curved surface impingement configuration) that shows up in a typical gas turbine impingement problem in relation to heat transfer. Impingement problems are difficult to simulate numerically using conventional RANS models. It is worth noting that the typical RANS model contains a number of calibrated constants and these have been formulated with respect to relatively simple shear flows. As a result typically these isotropic eddy viscosity models fail in predicting the correct heat transfer value and trend in impingement problem where the flow is highly anisotropic. The common RANS-based models over predict stagnation heat transfer coefficients by as much as 300% when compared to measured values. Even the best of the models, the v^2-f model, can be inaccurate by up to 30%. Even though there is myriad number of experimental and numerical work published on single jet impingement; the knowledge gathered from these works cannot be applied to real engineering impingement cooling application as the dynamics of flow changes completely. This study underlines the lack of experimental flow physics data in published literature on multiple jet impingement and the author emphasized how important it is to have experimental data to validate CFD tools and to determine the suitability of Large Eddy Simulation (LES) in industrial application. In the open literature there is not enough study where experimental heat transfer and flow physics data are combined to explain the behavior for gas turbine impingement cooling application. Often it is hard to understand the heat transfer behavior due to lack of time accurate flow physics data hence a lot of conjecture has been made to explain the phenomena. The problem is further exacerbated for array of impingement jets where the flow is much more complex than a single round jet. The experimental flow field obtained from Particle Image Velocimetry (PIV) and heat transfer data obtained from Temperature Sensitive Paint (TSP) from this work will be analyzed to understand the relationship between flow characteristics and heat transfer for the three types of novel geometry mentioned above.There has not been any effort made on implementing LES technique on array impingement problem in the published literature. Nowadays with growing computational power and resources CFD are widely used as a design tool. To support the data gathered from the experiment, LES is carried out in narrow wall impingement cooling configuration. The results will provide more accurate information on impingement flow physics phenomena where experimental techniques are limited and the typical RANS models yield erroneous resultThe objective of the current study is to provide a better understanding of impingement heat transfer in relation to flow physics associated with it. As heat transfer is basically a manifestation of the flow and most of the flow in real engineering applications is turbulent, it is very important to understand the dynamics of flow physics in an impingement problem. The work emphasis the importance of understanding mean velocities, turbulence, jet shear layer instability and its importance in heat transfer application. The present work shows detailed information of flow phenomena using Particle Image Velocimetry (PIV) in a single row narrow impingement channel. Results from the RANS and LES simulations are compared with Particle Image Velocimetry (PIV) data. The accuracy of LES in predicting the flow field and heat transfer of an impingement problem is also presented the in the current work as it is validated against experimental flow field measured through PIV.Results obtained from the PIV and LES shows excellent agreement for predicting both heat transfer and flow physics data. Some of the key findings from the study highlight the shortcomings of the typical RANS models used for the impingement heat transfer problem. It was found that the stagnation point heat transfer was over predicted by as much as 48% from RANS simulations when compared to the experimental data. A lot of conjecture has been made in the past for RANS' ability to predict the stagnation point heat transfer correctly. The length of the potential core for the first jet was found to be ~ 2D in RANS simulations as oppose to 1D in PIV and LES, confirm the possible underlying reason for this discrepancy. The jet shear layer thickness was underpredicted by ~ 40% in RANS simulations proving the model is not diffusive enough for a flow like jet impingement. Turbulence production due to shear stress was over predicted by ~130% and turbulence production due to normal stresses were underpredicted by ~40 % in RANS simulation very close to the target wall showing RANS models fail where both strain rate and shear stress plays a pivotal role in the dynamics of the flow. In the closing, turbulence is still one of the most difficult problems to solve accurately, as has been the case for about a century. A quote below from the famous mathematician, Horace Lamb (1849-1934) express the level of difficulty and frustration associated with understanding turbulence in fluid mechanics. (")I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.(")Source: http://scienceworld.wolfram.com/biography/Lamb.htmlThis dissertation is expected to shed some light onto one specific example of turbulent flows.
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Date Issued
2016
Identifier
CFE0006463, ucf:51424
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006463