There has been lots of interest in designing more fuel efficient aircraft using concepts such as boundary layer ingestion (BLI) that cause large amounts of pressure and swirl distortion that enter the jet engines. To enable ground testing the performance of these engines in different distortion patterns, the StreamVane and ScreenVane systems have been developed. A StreamVane consists of a complex vane pack that is custom designed for each distortion profile and the ScreenVane combines the StreamVane with a pressure distortion screen for testing engines under both pressure and swirl distortions. The complexity and uniqueness of these devices make predicting their structural integrity and propensity to flutter a challenge, necessitating the need for studying flutter in these complex vane packs. In order to study flutter of these complex vane packs, a methodology was created to obtain trailing edge displacements and frequencies from high speed video of a StreamVane and was used on a quad swirl StreamVane and a Simplified model. Unsteady CFD with periodic mesh deformation based off of its modal analysis was used to validate if it can predict the flutter velocity as well as understanding what the unsteady aerodynamic response to flutter is. A parameter study was then conducted along with oilflow visualization to better understand the potential causes of flutter and the impact of different design parameters. A harmonic response analysis was conducted on each of these designs and a correlation between the amplitude from the harmonic response and the flutter Mach number was obtained that can be used to predict when a StreamVane will flutter. A new series of StreamVanes were designed and based off of computational analysis, two were selected for manufacture. They both successfully avoided fluttering in flutter tests and were found to accurately replicate the goal swirl profile when measured with a 5 hole probe. These results provide a basis for understanding and predicting flutter in StreamVanes. / Master of Science / There has been lots of interest in designing more fuel efficient aircraft using concepts such as boundary layer ingestion (BLI) that cause large amounts of pressure and swirl distortion that enter the jet engines. To enable ground testing the performance of these engines in different distortion patterns, the StreamVane and ScreenVane systems have been developed. A StreamVane consists of a complex vane pack that is custom designed for each distortion profile and the ScreenVane combines the StreamVane with a pressure distortion screen for testing engines under both pressure and swirl distortions. The complexity and uniqueness of these devices make predicting their structural integrity and propensity to flutter a challenge, necessitating the need for studying flutter in these complex vane packs. Flutter is when a structure experiences excess vibration when exposed to unsteady aerodynamic loads. In order to study flutter of these complex vane packs, a methodology was created to obtain trailing edge displacements and frequencies from high speed video of a StreamVane and was used on a quad swirl StreamVane and a Simplified model. Unsteady computation fluid dynamics (CFD) with periodic mesh deformation was used to validate if it can predict the flutter velocity as well as understanding what the unsteady aerodynamic response to flutter is. A parameter study was then conducted along with oilflow visualization to better understand the potential causes of flutter and the impact of different design parameters. A harmonic response analysis, which consists of a dynamic structural analysis with sinusoidal loading applied, was conducted on each of these designs. A correlation between the amplitude from the harmonic response and the flutter Mach number was obtained that can be used to predict when a StreamVane will flutter. A new series of StreamVanes were then designed and based off of computational analyses, two were selected for manufacture. They both successfully avoided fluttering in flutter tests and were found to accurately replicate the goal swirl profile when measured with a 5 hole probe downstream of the StreamVane. These results provide a basis for understanding and predicting flutter in StreamVanes and other complex vane packs.

There is a present need for simulation and measuring the inlet swirl distortion generated by airframe/engine system interactions to identify potential degradation in fan performance and operability in a full-scale, ground testing environment. Efforts are described to address this need by developing and characterizing methods for complex, prescribed distortion patterns. A relevant inlet swirl distortion profile that mimics boundary layer ingesting inlets was generated by a novel new method, dubbed the StreamVane method, and measured in a sub scale tunnel using stereoscopic particle image velocimetry (SPIV) as a precursor for swirl distortion generation and characterization in an operating turbofan research engine. Diagnostic development efforts for the distortion measurements within the research engine paralleled the StreamVane characterization. The system used for research engine PIV measurements is described. Data was obtained in the wake of a total pressure distortion screen for engine conditions at idle and 80% corrected fan speed, and of full-scale StreamVane screen at 50% corrected fan speed. The StreamVane screen was designed to generate a swirl distortion that is representative for hybrid wing body applications and was made of Ultem*9085 using additive manufacturing. Additional improvements to the StreamVane method are also described. Data reduction algorithms are put forth to reduce spurious velocity vectors. Uncertainty estimations specific to the inlet distortion test rig, including bias error due to mechanical vibration, are made. Results indicate that the methods develop may be used to both generate and characterize complex distortion profiles at the aerodynamic interface plane, providing new information about airframe/engine integration. / Master of Science

A comprehensive computational and experimental analysis has been conducted to characterize the flow dynamics and periodic structures formed in the wake of complex turning vanes. The vane packs were designed by the StreamVane swirl distortion generator technology, a design system that can efficiently reproduce swirl distortion for compressor rig and full turbofan engine testing. StreamVanes consist of an array of turning vanes that commonly contain variations in turning angle along their span, a nonaxisymmetric profile about the centerline, and vane-to-vane intersections or junctions to accurately generate the desired distortion. In this study, vane packs are considered complex if they contain two out of three of these features, a combination seen in other turbomachinery components outside of StreamVane design. Similar to all stator vanes or rotor blades, StreamVane vane packs are constructed using a series of cross-sectional airfoil profiles with blunt trailing edges and finite thicknesses. This, in turn, introduces periodic vortex structures in the wake, commonly known as trailing edge vortex shedding. To fully understand how the dynamics and coherent wake formations within vortex shedding impact both the flow distortion and structural durability of StreamVanes, it is first necessary to characterize the corresponding wakes in three dimensions. The current study provides an in-depth analysis to predict and measure the trailing edge vortex development using high-fidelity computational fluid dynamics and stereoscopic time-resolved particle image velocimetry experiments. Two testcase StreamVane geometries were specifically designed with complex features to evaluate their influence on the dynamics and coherence of the respective vane wakes. Fully three-dimensional, unsteady computational fluid dynamics simulations were performed using a Reynolds-Averaged Navier-Stokes solver coupled with a standard two-equation turbulence model and a hybrid, scale-resolving turbulence model. Both models predicted large-scale wake frequencies within 1—14% of experiment, with a mean difference of less than 3.2%. These comparisons indicated that lower fidelity simulations were capable of accurately capturing such flows for complex vane packs. Additionally, structural and modal analyses were conducted using finite element models to determine the correlations between dominant structural modes and dominant wake (flow) modes. The simulations predicted that vortex shedding modes generally contained frequencies 300% larger than dominant structural modes, and therefore, vortex induced vibrations were unlikely to occur. Lastly, mode decomposition methods were applied to the experimental results to extract energy ratios and reveal dynamic content across high-order wake modes. The vortex shedding modes generated more than 80% of the total wake energy for both complex vane packs, and dynamic decomposition methods revealed unique structures within the vane junction wake. In all analyses, comparisons were made between different vane parameters, such as trailing edge thickness and turning angle, where it was found that trailing edge thickness was the dominant vortex shedding parameter. The motivation, methodology, and results of the following research is presented to better understand the wake interactions, computational predictive capabilities, and structural dynamics associated with vortex shedding from complex vane packs. Although the results directly relate to StreamVane distortion generator technology, the qualitative and quantitative comparisons between the selected methods, geometry parameters, and flow conditions can be extrapolated to modern turbomachinery components in general. Therefore, this dissertation aims to benefit distortion generator and turbomachinery designers by providing insight into the underlying physics and overall modeling techniques of the wake dynamics in highly three-dimensional, complex components. / Doctor of Philosophy / A comprehensive analysis has been completed to characterize the unsteady wake flow produced by complex turning vane systems in three dimensions. Turning vanes are a common component utilized in the field of fluid dynamics and aerospace propulsion to effectively turn and manipulate the working fluid to the desired condition. For propulsion applications, similar vanes can alleviate performance losses by improving the overall aerodynamics and mitigating flow distortions entering the compressor of a jet engine. Conversely, complex turning vanes can also be used to reproduce the distortion for engineers to evaluate jet engine components when subjected to nonuniform flow ingestion. The distinct geometry features that make these vanes complex are also present in other turbomachinery systems outside of distortion generation. In any case, the cross-sectional profiles of the turning vanes commonly contain blunt ends or trailing edges due to engineering limitations and/or restrictions. This geometric feature introduces periodic wake structures, known as vortex shedding, that can negatively effect the performance of the overall system. It is therefore a necessity to characterize both the dynamics and coherence of vortex shedding to fully understand the flow features in highly three-dimensional flows. In the presented research, this is achieved by applying computational simulations and experimental measurements to extract the corresponding wake dynamics of complex vane packs. The selected testcases where designed using the StreamVane technology, a mature system that generates tailored turning vanes to reproduce flow distortion in jet engine or fan rig ground-testing facilities. The fluid simulations captured the expected wake flow and largescale structures convecting downstream of the vane packs. A comparison between two different flow models and the experimental results revealed minimal quantitative differences in the large-scale dynamics, which gave insight into the model selection to predict such flows. Additional structural simulations were performed to estimate the forcing and response of the vane packs when subjected to the aerodynamic loading. The results showed vortex shedding was highly unlikely to cause large amplitude vibrations and structural failures. In all analyses, the primary results were correlated with common vane parameters and operating conditions to evaluate their impact on the wake dynamics. The motivation, methodology, and results of the following research is presented to better understand the wake interactions, computational predictive capabilities, and structural dynamics associated with vortex shedding from complex vane packs. Although the results directly relate to StreamVane distortion generator technology, the qualitative and quantitative comparisons between the selected methods, geometry parameters, and flow conditions can be extrapolated to modern turbomachinery components in general. Therefore, this dissertation aims to benefit distortion generator and turbomachinery designers by providing insight into the underlying physics and overall modeling techniques of the wake dynamics in highly three-dimensional, complex components.

Significant effort in the current technological development of aircraft is aimed at improving engine efficiency, while reducing fuel burn, emissions, and noise levels. One way to achieve these is to better integrate airframe and propulsion system. Tighter integration, however, may also cause adverse effects to the flow entering the engines, such as total pressure, total temperature, and swirl distortions. Swirl distortions are angular non-uniformities in the flow that may alter the functioning of specific components of the turbomachinery systems. To investigate the physics involved in the ingestion of swirl, pre-determined swirl distortion profiles were generated through the StreamVane method in a low-speed wind tunnel and in a full-scale turbofan research engine. Stereoscopic particle image velocimetry (PIV) was used to collect three-component velocity fields at discrete planes downstream of the generation of the distortions with two main objectives in mind: identifying the physics behind the axial development of the distorted flow; and describing the generation of the distortion by the StreamVane and its impact to the flow as a distortion generating device. Analyses of the mean velocity, velocity gradients, and Reynolds stress tensor components in these flows provided significant insight into the driving physics. Comparisons between small-scale and full-scale results showed that swirl distortions are Mach number independent in the subsonic regime. Reynolds number independence was also verified for the studied cases. The mean secondary flow and flow angle profiles demonstrated that the axial development of swirl distortions is highly driven by two-dimensional vortex dynamics, when the flow is isolated from fan effects. As the engine fan is approached, the vortices are axially stretched and stabilized by the acceleration of the flow. The flow is highly turbulent immediately downstream of the StreamVane due to the presence of the device, but that vane-induced turbulence mixes with axial distance, so that the device effects are attenuated for distances greater than a diameter downstream, which is further confirmed by the turbulent length scales of the flow. These results provide valuable insight into the generation and development of swirl distortion for ground-testing environments, and establishes PIV as a robust tool for engine inlet investigations. / Ph. D.

The aerodynamic integration of an aero-engine intake system with the airframe can pose some notable challenges. This is particularly so for many military air- craft and is likely to become a more pressing issue for both new military systems with highly embedded engines as well as for novel civil aircraft configurations. During the late 1960s with the advent of turbo-fan engines, industry became in- creasingly aware of issues which arise due to inlet total pressure distortion. Since then, inlet-engine compatibility assessments have become a key aspect of any new development. In addition to total temperature and total pressure distortions, flow angularity and the associated swirl distortion are also known to be of notable con- cern. The importance of developing a rigorous methodology to understand the effects of swirl distortion on turbo-machinery has also become one of the major concerns of current design programmes. The goal of this doctoral research was to further the current knowledge on swirl distortion, and its adverse effects on engine performance, focusing on the turbo-machinery components (i.e. fans or compressors). This was achieved by looking into appropriate swirl flow descriptors and by correlating them against the compressor performance parameters (e.g loss in stability pressure ratios). To that end, a number of high-fidelity three-dimensional Computational Fluid Dynamics (CFD) models have been developed using two sets of transonic rotors (i.e. NASA Rotor 67 and 37), and a stator (NASA Stator 67B). For the numerical purpose, a boundary condition methodology for the definition of swirl distortion patterns at the inlet has been developed. Various swirl distortion numerical parametric studies have been performed using the modelled rotor configurations. Two types of swirl distortion pattern were investigated in the research, i.e. the pure bulk swirl and the tightly-wound vortex. Numerical simulations suggested that the vortex core location, polarity, size and strength greatly affect the compressor performance. The bulk swirl simula- tions also showed the dependency on swirl strength and polarity. This empha- sized the importance of quantifying these swirl components in the flow distortion descriptors. For this, a methodology have been developed for the inlet-engine compatibility assessment using different types of flow descriptors. A number of correlations have been proposed for the two types of swirl distortion investigated in the study.

The aerodynamic integration of an aero-engine intake system with the airframe can pose some notable challenges. This is particularly so for many military air- craft and is likely to become a more pressing issue for both new military systems with highly embedded engines as well as for novel civil aircraft configurations. During the late 1960s with the advent of turbo-fan engines, industry became in- creasingly aware of issues which arise due to inlet total pressure distortion. Since then, inlet-engine compatibility assessments have become a key aspect of any new development. In addition to total temperature and total pressure distortions, flow angularity and the associated swirl distortion are also known to be of notable con- cern. The importance of developing a rigorous methodology to understand the effects of swirl distortion on turbo-machinery has also become one of the major concerns of current design programmes. The goal of this doctoral research was to further the current knowledge on swirl distortion, and its adverse effects on engine performance, focusing on the turbo-machinery components (i.e. fans or compressors). This was achieved by looking into appropriate swirl flow descriptors and by correlating them against the compressor performance parameters (e.g loss in stability pressure ratios). To that end, a number of high-fidelity three-dimensional Computational Fluid Dynamics (CFD) models have been developed using two sets of transonic rotors (i.e. NASA Rotor 67 and 37), and a stator (NASA Stator 67B). For the numerical purpose, a boundary condition methodology for the definition of swirl distortion patterns at the inlet has been developed. Various swirl distortion numerical parametric studies have been performed using the modelled rotor configurations. Two types of swirl distortion pattern were investigated in the research, i.e. the pure bulk swirl and the tightly-wound vortex. Numerical simulations suggested that the vortex core location, polarity, size and strength greatly affect the compressor performance. The bulk swirl simula- tions also showed the dependency on swirl strength and polarity. This empha- sized the importance of quantifying these swirl components in the flow distortion descriptors. For this, a methodology have been developed for the inlet-engine compatibility assessment using different types of flow descriptors. A number of correlations have been proposed for the two types of swirl distortion investigated in the study.

<p>The purpose of this research was to determine what components of a complex centrifugal  compression system inlet needed to be modelled to accurately predict the swirl and total pressure  distortions at the compressor face. Two computational models were developed. A full-fidelity case  where all the inlet geometry was modelled and a reduced model where a small portion of the inlet  was considered. Both the numerical cases were compared with experimental data from a research  compressor rig developed by Honeywell Aerospace. The test apparatus was designed with a  modular inlet system to develop swirl distortion patterns. The modular inlet system utilized  transposable baffles within the radial-to-axial section of the inlet and blockage plates of varying  sizes and geometries at the inlet to this section.  Discerning the dominant inlet component that dictates distortion behavior at the compressor  face would allow the reduced modelling of inlet components for compression systems and would  allow coupling with more tortuous systems. Furthermore, it would reduce the design iteration and  simulation time of the inlet systems. Several investigations utilizing a reduced model only  considering a radial-to-axial inlet are available in literature, but no comprehensive justification has  been presented as to the impact this has on the distortion behavior.   Experimental surveys of flow conditions just upstream of the inducer of the centrifugal  compressor were conducted at several operating conditions. The highest and lowest mass flow  rates of these operating points were simulated using ANSYS CFX 2020R1 for both the  computational models. Multiple inlet configurations were simulated to test the robustness of the  reduced model in comparison to the full fidelity. The numerical simulations highlighted  shortcomings of the instrumentation used to characterize the experimental flow field at the inducer,  particularly with respect to total pressure distortion. Furthermore, transient pressure data were  measured in experiment and indicated unsteady fluctuations in the inlet that would not be captured  by steady computational fluid dynamic simulations. These data matched locations of disagreement  with swirl distortion behavior at high mass flow rates. This suggested that transient vortex  movement occured at the aerodynamic interface plane in certain configurations.   The total pressure distortion metrics between the two models were remarkably comparable.  Furthermore, the simplified model accurately predicted the mixing losses associated with the  blockage plates at the inlet to the radial-to-axial inlet using a simple inlet extension. Swirl  18  distortion was dictated by the radial-to-axial inlet. The reduced model data trends were comparable  with experiment for both the baffle and blocker plate configurations. The swirl intensities for all  configurations were comparable between the two models. The reduced model swirl directivity  trends matched those of experiment. The most notable deviations between the full-fidelity model  and the reduced model were observed with swirl directivity numerics. </p>