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Author: Cody R. Ground Publisher: ISBN: Category : Aerodynamics, Supersonic Languages : en Pages : 172
Book Description
The scramjet engine offers the unique capability to enable sustained air breathing flight at hypersonic speeds. However, in order to reach its full application potential, further technological maturation of several system level components is necessary. One such component is the fuel injection system. The flow conditions characteristic of the scramjet combustor are such that the rate-limiting step in the fuel injection/mixing/combustion process is the mixing of the fuel and air. For this reason, the fuel injection system must be designed with the goal of enhancing the rate of fuel/air mixing. One method that has shown potential to enhance fuel/air mixing in supersonic flows is the introduction of streamwise vorticity into the mixing field, yet there are many fundamental aspects of this concept that remain relatively uninvestigated. One such aspect is the capability to use specific streamwise vortex interaction modes to synergistically increase mixing in the flow. However, in order to target specific vortex interactions which act to enhance mixing in the design stage of a fuel injection system a better foundational knowledge of streamwise vortex interactions in supersonic flows must be obtained. To this end, this dissertation presents a fundamental experimental investigation into two elemental modes of vortex interaction, the merging and non-merging of a pair of co-rotating streamwise vortices. The experimental investigations were all conducted at the University of Texas at Arlington Aerodynamics Research Center in the blow-down Supersonic Wind Tunnel Facility which delivered a Mach 2.5 free stream flow for all of the experiments detailed herein. To create the targeted vortex interaction modes specific configurations of vortex generating ramps were affixed to the trailing edge of a strut injector. The experiments detailed in this dissertation accomplish two tasks in the continuation of the group's previous research on the merging and non-merging modes of streamwise vortex interaction. The first task that will be presented is the analysis of the fluctuating velocity flow fields of the two studied vortex interactions with the proper orthogonal decomposition (POD) technique. This analysis is approached in order to quantify the organization and relative turbulent kinetic energy content of the various scales of turbulent coherent structures of the flow. The results of the POD analysis revealed that the vortex merging process reorients and redistributes the turbulent kinetic energy content towards the larger coherent structures captured in the low-order eigenmodes of the POD. The second task presented in this dissertation is the non-intrusive laser-based quantification of the mixing performance of the two vortex interactions using the filtered Rayleigh scattering (FRS) technique. Applying the FRS technique to retrieve mixture composition measurements in highly complex flows such as the flows studied here is a nontrivial task. For this reason, experiments were initially performed in a canonical two-dimensional planar shear layer to compare the relative accuracy of filtered Rayleigh scattering measurements with intrusive gas-sampling based mixture composition measurements. With this comparison yielding good levels of agreement between the two techniques, the FRS technique was able to be confidently applied in the vortical flows of primary interest. The main conclusion obtained from the FRS experiments was the finding that the non-merging vortex interaction more rapidly mixes the fuel and air due to its increased rate of entrainment with respect to the merging vortex interaction. Taken together, the results of the two analyses presented in this dissertation highlight the necessity of considering streamwise vortex interactions in the design stage of scramjet fuel injection systems since all differences in the flowfields of the two studied cases arise solely due to the different vortex interaction modes generated. Most importantly, this work has laid the foundation for future fundamental vortex dynamics studies which seek to optimize these (and other) modes of interaction by using the analysis and measurement techniques described herein.
Author: Cody R. Ground Publisher: ISBN: Category : Aerodynamics, Supersonic Languages : en Pages : 172
Book Description
The scramjet engine offers the unique capability to enable sustained air breathing flight at hypersonic speeds. However, in order to reach its full application potential, further technological maturation of several system level components is necessary. One such component is the fuel injection system. The flow conditions characteristic of the scramjet combustor are such that the rate-limiting step in the fuel injection/mixing/combustion process is the mixing of the fuel and air. For this reason, the fuel injection system must be designed with the goal of enhancing the rate of fuel/air mixing. One method that has shown potential to enhance fuel/air mixing in supersonic flows is the introduction of streamwise vorticity into the mixing field, yet there are many fundamental aspects of this concept that remain relatively uninvestigated. One such aspect is the capability to use specific streamwise vortex interaction modes to synergistically increase mixing in the flow. However, in order to target specific vortex interactions which act to enhance mixing in the design stage of a fuel injection system a better foundational knowledge of streamwise vortex interactions in supersonic flows must be obtained. To this end, this dissertation presents a fundamental experimental investigation into two elemental modes of vortex interaction, the merging and non-merging of a pair of co-rotating streamwise vortices. The experimental investigations were all conducted at the University of Texas at Arlington Aerodynamics Research Center in the blow-down Supersonic Wind Tunnel Facility which delivered a Mach 2.5 free stream flow for all of the experiments detailed herein. To create the targeted vortex interaction modes specific configurations of vortex generating ramps were affixed to the trailing edge of a strut injector. The experiments detailed in this dissertation accomplish two tasks in the continuation of the group's previous research on the merging and non-merging modes of streamwise vortex interaction. The first task that will be presented is the analysis of the fluctuating velocity flow fields of the two studied vortex interactions with the proper orthogonal decomposition (POD) technique. This analysis is approached in order to quantify the organization and relative turbulent kinetic energy content of the various scales of turbulent coherent structures of the flow. The results of the POD analysis revealed that the vortex merging process reorients and redistributes the turbulent kinetic energy content towards the larger coherent structures captured in the low-order eigenmodes of the POD. The second task presented in this dissertation is the non-intrusive laser-based quantification of the mixing performance of the two vortex interactions using the filtered Rayleigh scattering (FRS) technique. Applying the FRS technique to retrieve mixture composition measurements in highly complex flows such as the flows studied here is a nontrivial task. For this reason, experiments were initially performed in a canonical two-dimensional planar shear layer to compare the relative accuracy of filtered Rayleigh scattering measurements with intrusive gas-sampling based mixture composition measurements. With this comparison yielding good levels of agreement between the two techniques, the FRS technique was able to be confidently applied in the vortical flows of primary interest. The main conclusion obtained from the FRS experiments was the finding that the non-merging vortex interaction more rapidly mixes the fuel and air due to its increased rate of entrainment with respect to the merging vortex interaction. Taken together, the results of the two analyses presented in this dissertation highlight the necessity of considering streamwise vortex interactions in the design stage of scramjet fuel injection systems since all differences in the flowfields of the two studied cases arise solely due to the different vortex interaction modes generated. Most importantly, this work has laid the foundation for future fundamental vortex dynamics studies which seek to optimize these (and other) modes of interaction by using the analysis and measurement techniques described herein.
Author: Davide Viganó Publisher: ISBN: Category : Aerodynamics, Supersonic Languages : en Pages : 137
Book Description
The development of effective mixing strategies of air/fuel mixtures in supersonic flows has been the subject of a significant body of research for the last 60 years due to the hindering effects of compressibility. Particular attention has been focused on the introduction of streamwise vortices as a way to enhance molecular mixing both in terms of added source for hydrodynamic instabilities on classical shear-layer flows as well as for transverse jet configurations, aero-ramps and hypermixers. However, a large portion of fundamental knowledge for these complex flows is still missing. This work is centered on a numerical and experimental study of turbulence transport and dynamics associated with pre-selected modes of vortex interactions. A numerical study was initially performed to engineer a unique interaction between supersonic streamwise vortices such as the production of turbulent kinetic energy is maintained at a positive level. This analysis was conducted by using the in-house developed VorTx code after been upgraded by the author to allow for the correct calculation of derived quantities such as strain rates via a new application of vortex-blob methods in supersonic flows. The successive experimental investigation of the selected vortex interaction has successfully confirmed a positive turbulent kinetic energy production for all sampled stations, thus confirming the initial prediction. No other case investigated to this date in our research group or in the available literature, to the best knowledge of the author, has ever shown these results. A detailed analysis on the interaction of the resulting mean ow strain rates and the Reynolds stresses is presented in this work as well as the contribution of this analysis on the augmented understanding of these complex flows. It was found that turbulence anisotropy plays a critical role for turbulent kinetic energy production. The results of this work are critical for the design of efficient hypersonic air-breathing propulsion systems.
Author: Fabrizio Vergine Publisher: ISBN: Category : Aerodynamics, Supersonic Languages : en Pages : 213
Book Description
Despite the recognized importance of streamwise vortices in the enhancement of fuel/air mixing processes in scramjet combustors, the effects of their interactions and dynamics on mixing and associated total pressure losses are still relatively unexplored. This work presents the first systematic effort to find answers to fundamental questions such as: can selected vortex interactions be identified and effectively used in an injection system for scramjets? Is the increase of streamwise vorticity content, regardless of its spatial distribution in the flow, always beneficial for entrainment and molecular mixing? Is it possible to apply vortex dynamics concepts in reacting flows? For this reason the dissertation covers the study of selected vortex interaction scenarios both in cold and high enthalpy reacting flows. Specifically, the experimental results and the analysis of the flowfields resulting from two selected supersonic vortex interaction modes in a Mach 2.5 cold flow are presented. Additionally, the experiment design based on vortex dynamics concepts and the reacting plume survey of two pylon injectors in a Mach 2.4 high enthalpy flow are shown. The cold flow experiments were conducted in the supersonic wind tunnel of the Aerodynamics Research Center at the University of Texas at Arlington. A strut injector equipped with specified ramp configurations was designed and used to produce the flowfields of interest. The reacting flow experiments were conducted in the Expansion Tube Facility located in the High Temperature Gasdynamics Laboratory of Stanford University. A detailed description of the supersonic wind tunnel, the instrumentation, the strut injector and the supersonic wake flow downstream is shown as part of the characterization of the facility. As stereoscopic particle image velocimetry was the principal flow measurement technique used in this work to probe the streamwise vortices shed from ramps mounted on the strut, this dissertation provides a deep overview of the challenges and the application of the aforementioned technique to the survey of vortical flows. Moreover, the dissertation provides a new and comprehensive analysis of the flow physics associated with these complex supersonic vortical interactions. The mean and fluctuating velocity flowfields of two selected vortex dynamics scenarios, chosen based on the outcomes of the simulations of an inviscid reduced order model developed in the research group, are presented. The same streamwise vortices (strength, size and Reynolds number) were used experimentally to investigate both a case in which the resulting dynamics evolve in a vortex merging scenario and a case in which the merging process is voluntarily avoided in order to focus the analysis on the fundamental differences associated with the amalgamation processes alone. The results from the mean flow highlight major differences between the two cases and corroborate the use of an inviscid model for the prediction of the main flow physics in the times scales considered. The analysis is also extended to turbulence quantities and concepts borrowed from incompressible turbulence theory (i.e., fluctuating Mach numbers “ 1) appear to explain interesting features of the fluctuating flowfields. Once the interactions among the vortical structures in cold flow were assessed, these vortex dynamics concepts were probed in a reacting environment. The dissertation describes the design phase of two pylon injectors based on the prediction capabilities of the aforementioned model. Then, the results of a set of combustion experiments conducted utilizing hydrogen fuel injected into a Mach 2.4, high-enthalpy (2.8 MJ/kg) air flow are discussed. The results show that, for the heat release levels considered in this study, the morphology of the plume and its evolution are remarkably close to the results produced by the model, enabling an interpretation based on vortex dynamics considerations. The persistence of the streamwise vortical structures created by the selected ramp configurations is shown together with the effectiveness of the coherent structures in successfully anchoring the flame very close to the injection point. The work shows the possibility of a new approach in the design of injection strategies (not limited to injection devices) suitable for adoption in scramjet combustors based on the ability to predict, with basic vortex dynamics concepts and a highly reduced computational cost, the main features of flows of technological interest.
Author: Vijay Gopal Publisher: ISBN: Category : Airplanes Languages : en Pages : 175
Book Description
Mixing enhancement in supersonic flow is an important domain of research for enabling the realization of efficient and scalable high speed air-breathing engines (scramjet).Introducing streamwise vorticies in supersonic flow and tailoring their interactions for mixing enhancement is the primary motivation for the present research study. Leveraging the research performed in the group at the Aerodynamics Research Center (ARC), systematic experimental studies on mixing enhancement is carried out in supersonic flows by tailoring the selected modes of stream wise vortex interactions with the aid of in-house developed reduced order method VorTX. This method utilizes the lifting line-vortex theory in supersonic flow to perform rapid simulations of streamwise vortex-interactions that serves as a guide to design the mixing experiments. One of the difficulties associated with scaling the simulations to higher Mach numbers (M > 4) arise from the strong influence of the singularities along the Mach cones emanating from the lifting line-vortex that results in physically inconsistent solution. In this work a fundamental study on vorticity distribution in linearized supersonic flow is carried out. The origin of the aforementioned singularities on the Mach cone is discussed in detail, and the potential candidates for vorticity distribution are proposed to eliminate the singularities and to provide a physically consistent solution of the flow field in supersonic flow. This study presents the successful solution for the elimination of the singularities that has allowed to extend the capability of VorTX to simulate vortex-interactions at higher Mach numbers. Experimental studies on supersonic mixing were carried out using a strut injection platform with vortex generating ramps to introduce streamwise voriticies in supersonic flow. The geometrical configuration of the ramps are chosen using the upgraded VorTX simulations to target the experimental study of two selected modes of vortex interactions. One is the merging of two co-rotating vorticies and the other is the non-merging case where the vorticies interact but do not merge. Mixing measurements in supersonic flow were carried out using the Filtered Rayleigh Scattering (FRS)technique. The measurement yields the mole-fraction of helium (injectant) in a binary mixture of air and helium in supersonic flow. The distributions of helium mole-fraction in the cross flow planes are used to draw conclusions on the level of mixing in the two modes of vortex-interaction. The FRS technique requires two independent experiments. One with helium injection in supersonic air flow and the other with air injection in an identical supersonic air flow. At a given cross-flow plane, to obtain the helium mole-fraction distribution using the FRS signals it is assumed that the total number density is matched in both the experiments. To enhance the reliability of the FRS measurement technique, it is important to minimize and quantify the systematic errors that arise from the assumptions made, particularly, the assumption on matching the total number density. In this work, a method to reduce the systematic errors in FRS experiments is proposed for a canonical case study of a rectangular jet in supersonic flow. To do this, a reduced order model for a rectangular jet in supersonic air flow is successfully developed in order to guide the selection of appropriate injector's plenum conditions to minimize the systematic errors in the future FRS experiments and to retrospectively evaluate and correct the FRS measurements for systematic errors in previously available FRS data on parallel strut injection in supersonic flow.
Author: Alexander J. Smits Publisher: Springer Science & Business Media ISBN: 0387263055 Category : Science Languages : en Pages : 418
Book Description
A good understanding of turbulent compressible flows is essential to the design and operation of high-speed vehicles. Such flows occur, for example, in the external flow over the surfaces of supersonic aircraft, and in the internal flow through the engines. Our ability to predict the aerodynamic lift, drag, propulsion and maneuverability of high-speed vehicles is crucially dependent on our knowledge of turbulent shear layers, and our understanding of their behavior in the presence of shock waves and regions of changing pressure. Turbulent Shear Layers in Supersonic Flow provides a comprehensive introduction to the field, and helps provide a basis for future work in this area. Wherever possible we use the available experimental work, and the results from numerical simulations to illustrate and develop a physical understanding of turbulent compressible flows.
Author: Thomas Paul Fetterhoff Publisher: ISBN: Category : Aerodynamics Languages : en Pages : 145
Book Description
This study presents results of innovative integration of passive and active flow physics to accomplish effective supersonic mixing. The study is continuing cavity flow control research in the supersonic wind tunnel at the University of Tennessee Space Institute (UTSI). Initially numerical simulations were employed in support of choosing and refining the experimental configuration designs. Mixing enhancement was achieved through innovative coupling of aerodynamics of corner vortex flows and cavity flow control jets. The two geometries were chosen for their potential to generate strong streamwise vortices, weaker shock losses, low drag, and cavity recirculation zones. Another consideration was that the two physically different concepts would be studied to provide better understanding of the innovative mixing. Jets, simulating fuel injection, were used for flow control provided through penetrations in the front face and side walls of the cavity. Flow visualization, dynamic pressure (sound pressure level) data are measured and PIV measurements are presented and compared with computational predictions for several geometries. High frequency dynamic pressure data were recorded to determine the cavity flow acoustic patterns. Measurements were acquired by a digital data acquisition system from two dynamic pressure transducers, located at different locations on the floor of the cavity. PIV measurements of selected configurations were performed. Schlieren and PIV images, pressure spectra and 2-D PIV data obtained are used as a basis for understanding the flow processes involved and comparison for improving the overall mixing and penetration performance. Streamwise vortices were generated using two different innovatively designed geometries, strategically located upstream of selected cavity configurations, including various jet arrangements, simulating fuel flow and control. Both configurations tested developed relatively strong streamwise vortex flows and weakened or lofted shear layers, indicating that mixing was enhanced. The two configurations exhibited flow changes with the simulated fuel injection. However, different injection arrangements by the simulated fuel jets resulted in different details in the flow fields and their resulting acoustic spectra. The resulting flow fields show improved potential for fuel flow mixing and increased penetration while amplifying or attenuating flow unsteadiness in the cavity.
Author: Cody R. Ground
Author: Cody R. Ground
Author: Davide Viganó
Author: Fabrizio Vergine
Author: Vijay Gopal
Author: Alexander J. Smits
Author: 
Author: 
Author: 
Author: 
Author: Thomas Paul Fetterhoff