Future commercial transport aircraft will feature more aerodynamic architectures to accommodate stringent design goals for higher fuel efficiency, reduced cruise and taxi NOx emissions, and reduced noise. Airframe designs most likely to satisfy the first goal feature architectures that lead to the formation of non-uniform flow introduced to the engine through boundary layer ingesting (BLI) inlets, creating a different operational environment from which the engines were originally designed. The goal of this study was to explore the effects such non-uniform flow would have on the behavior and performance of a transonic fan in a full scale engine test environment. This dissertation presents an experimental study of the interaction between a full scale transonic fan and a total pressure distortion representative of a boundary layer ingesting serpentine inlet. A five-hole pneumatic probe was traversed directly in front of and behind a fan rotor to fully characterize the inlet and outlet fan profile. The distortion profile was also measured at the aerodynamic interface plane (AIP) with an SAE standard total pressure rake, which has historically been accepted as the inlet profile to the fan. This provided a comparison between the present work and current practice. Accurate calculation of local fan performance metrics such as blade loading, pressure rise, and efficiency were obtained. The fan inlet measurement profile greatly enhanced the understanding of the fan interaction to the flow distortion and provided a more complete explanation of the fan behavior. Secondary flowfield formation due to the accelerated flow redistribution directly upstream of the fan created localized bulk co- and counter- rotating swirl regions that were found to be correlated with localized fan performance phenomena. It was observed that the effects of the distortion on fan performance were exaggerated if the assumed fan inlet profiles were data taken only at the AIP. The reduction in fan performance with respect to undistorted inlet conditions is also explored, providing insight into how such distortions can be compared to baseline conditions. The dissertation closes with several recommendations for improving distortion tolerant fan design in the context of experimental research and development. / Ph. D.

Distortion tolerant fans represent the enabling technology for the successful implementation of highly integrated airframe propulsion system vehicles. This investigation extends the study of fan-distortion interactions to an actual turbofan engine with a total pressure distortion profile representative of a boundary-layer ingesting (BLI) embedded engine. The goal was to make a series of flow measurements that contribute to the overall physical understanding of this complex flow situation. Proper uncertainty analysis is critical to extracting meaning from the data measured in this study. The important information in the measurements is contained in small differences that lead to large impacts on the fan performance. In some cases, these differences were measured to a useful degree of accuracy, while in others they were not. One important application of the uncertainty analysis techniques developed in this work is the identification of the dominant error sources that resulted in unacceptable uncertainties. This dissertation presents an experimental study of transonic fan response to inlet total pressure distortion. A Pratt and Whitney JT15D-1 turbofan engine was subjected to a total pressure distortion representative of a boundary layer ingesting serpentine inlet. A 5-hole probe measured the aerodynamic response of the fan rotor in terms of flow angles, total pressure, and static pressure. A thermocouple embedded in the probe measured the rotor outlet total temperature. These measurements enabled the full characterization of the flow condition at each measurement point. The results indicate that a trailing edge separation and reattachment cycle experienced by the blades caused variations in the work input to the flow and resulted in a non-uniform rotor outlet flow profile. The details of the aerodynamic process and several means for improving distortion response are presented in this context. As a second theme, the modern measurement and uncertainty analysis techniques required to obtain useful information in this situation are developed and explored. Uncertainty analysis is often treated as a less glamorous afterthought in experimental research. However, as technology develops along lines of ever increasing system-level integration, simply suggesting the solution to a single flow situation does not repre- sent closure to the larger problem. In addition to frameworks for developing distortion tolerant fans, frameworks for developing frameworks are required. Uncertainty-drivenexperimental techniques represent the enabling methodology for the discovery and un- derstanding of the subtle phenomena associated with such coupled performance. These considerations are required to extend the usefulness of the results to the overarching issue of integrating the complex performance of individual components into an overall superior system. The experimental methods and uncertainty analysis developed in this study are presented in this context. / Ph. D.

An experimental investigation into the effects of inlet temperature transients on the stall and stall recovery aerodynamics of a low speed multi-stage axial flow compressor has been presented. Experiments were conducted on a low speed multi-stage axial flow compression system to demonstrate how a compressor dynamically stalls or recovers from a rotating stall operating condition during an inlet temperature transient. The specific effects of the inlet temperature transients on the compressor rotor blade flow physics during the dynamic stall or rotating stall recovery events of the axial flow compression system have been presented. In one experiment, a full recovery from a rotating stall operating condition was successfully accomplished on the low speed multistage axial flow compressor. Explanations for the axial flow compression system dynamic stall and rotating stall recovery processes during inlet temperature transients have been presented. The method utilized for inducing the rotating stall recovery on the compression system has been proposed as a possible new technique for active recovery from rotating stall for single and multi-stage axial flow compression systems. / Ph. D.

A new method for predicting forced vibratory blade response to total pressure distortion has been developed using modal and harmonic analysis. Total pressure distortions occur in gas turbine engines when the incoming airflow is partially blocked or disturbed. Distorted inlet conditions can have varying effects on engine performance and engine life. Short-term effects are often in the form of performance degradation where the distorted airflow causes a loss in pressure rise, and a reduction in mass flow and stall margin. Long-term effects are a result of vibratory blade response that can ultimately lead to high cycle fatigue (HCF), which in turn can quickly cause partial damage to a single blade or complete destruction of an entire compressor blade row, leading to catastrophic failure of the gas turbine engine. A better understanding and prediction of vibratory blade response is critical to extending engine life and reducing HCF-induced engine failures. This work covers the use of finite element modeling coupled with computational fluid dynamics-generated pressure fields to create a generalized forcing function. The first three modes of a low-aspect-ratio, transonic, first stage blade of a two-stage fan were examined. The generalized forcing function was decomposed to the frequency domain to identify the dominant harmonic magnitude present, as well as other contributing harmonics. An attempt to define the relationship between modal force with varying total pressure distortion levels produced a sensitivity factor that describes the relationship in the form of a simple multiplier. A generalized force was applied to the blade and varied harmonically across a frequency range known to contain the first natural frequency. The mean rotor stress variation was recorded and compared to experimental results to validate the accuracy of the model and verify its ability to predict vibratory blade response accurately. / Master of Science

A new method and mechanism for generating non-uniform, or distorted, aircraft engine inlet flow is being developed in order to account for dynamic changes during the creation and propagation of the distortion. Total pressure distortions occur in gas turbine engines when the incoming flow is disturbed. Dynamic total pressure changes may happen slowly, or may occur very rapidly. The disturbance of the incoming flow can change engine operating characteristics, including lowering the surge limit and creating High Cycle Fatigue incidents. In order to create a distorted flow with dynamic characteristics, a mechanism must be developed that when actuated, can change the distortion pattern and intensity with respect to time. This work covers the initial design of both the distorting and actuating device. The design chosen is a low force design that is practically independent of flow forces. This allows the system to be easily sized for all flow conditions. The study also includes developing the working design into an overall prototype. Testing is also performed to validate the design as the most advantageous choice. / Master of Science

Next generation aircraft design focuses on highly integrated airframe/engine architectures that exploit advantages in system level efficiency and performance. One such design concept incorporates boundary layer ingestion which locates the turbofan engine inlet near enough to the lifting surface of the aircraft skin that the boundary layer is ingested and reenergized. This process reduces overall aircraft drag and associated required thrust, resulting in fuel savings and decreased emissions; however, boundary layer ingestion also creates unique challenges for the turbofan engines operating in less than optimal inlet flow conditions. The engine inlet flow profiles predicted from boundary layer ingesting aircraft architectures contain complex distortions that affect the engine operability, durability, efficiency, and performance. One component of these complex distortion profiles is off-axial secondary flow, commonly referred to as swirl. As a means to investigate the interactions of swirl distortion with turbofan engines, an experiment was designed to measure distorted flow profiles in an operating turbofan research engine. Three-dimensional flow properties were measured at discrete planes immediately upstream and immediately downstream of the fan rotor, isolating the component for analysis. Constant speed tests were conducted under clean and distorted test conditions. For clean tests, a straight cylindrical inlet duct was attached to the fan case; for distorted tests, a StreamVane swirl distortion generator was inserted into the inlet duct. The StreamVane was designed to induce a swirl distortion matching results of computation fluid dynamics models of a conceptual blended wing body aircraft at a plane upstream of the fan. The swirl distortion was then free to develop naturally within the inlet duct before being ingested by the engine. Results from the investigation revealed that the generated swirl profile developed, mixed, and dissipated in the inlet duct upstream of the fan. Measurements immediately upstream of the fan rotor leading edge revealed 50% reduction in measured flow angle magnitudes along with evidence of fanwise vortex convection when compared to the StreamVane design profile. The upstream measurements also indicated large amounts of secondary flow entered the fan rotor. Measurements immediately downstream of the fan rotor trailing edge demonstrated that the fan processed the distortion and further reduced the intensity of the swirl; however, non-uniform secondary flow persisted at this plane. The downstream measurements confirmed that off-design conditions entered the fan exit guide vanes, likely contributing to cascading performance deficiencies in downstream components and reducing the performance of the propulsor system. / Master of Science

The rising interest in fan performance in the presence of total pressure distortion, a topic of fundamental interest for integrated airframe/engine architectures, has led to increased research in ground based testing environments. Included in these studies is the generation of simulated total pressure distortion profiles using wire mesh screens. Although the inlet duct development of total pressure distortion patterns has been studied in a historical context when distortion effects on engine performance were first of interest, these were typically simplified experimental studies for low-speed flows. To aid in the understanding of total pressure distortion development approaching a transonic fan face, a series of experiments were conducted to detail the development of such a profile downstream of the screen plane in the absence and presence of fan effects. Presented is an extensive experimental set to detail (1) the evolution of a screen-generated total pressure distortion profile as it develops in a constant diameter inlet duct and (2) the effect that a single stage transonic fan has on the distortion development. Included is a detailed analysis of the distortion profile characteristics for increasing development length, and the behavioral changes of the profile when fan blockage is present near the screen plane. Recommendations are made regarding the placement of total pressure distortion screens relative to the fan face, and insights are given into the expected profile evolution. This work is a contributing part of an ongoing systematic investigation of fan performance when subjected to screen-generated total pressure inlet distortion. / Master of Science

Boundary Layer Ingestion (BLI) is currently being researched as a potential method to improve efficiency and decrease emissions for the next generation of commercial aircraft.  While re-energizing the boundary layer formed over the fuselage of an aircraft has many system level benefits, ingesting the low velocity boundary layer flow through a serpentine inlet into a turbofan engine adversely affects the performance of the engine.  The available literature has only yielded studies of the effects of this specific type of inlet distortion on engine performance in the form of numerical simulations.  This work seeks to provide an experimental analysis of the effects of BLI-type distortion on a turbofan engine's performance.  A modified JT15D-1 turbofan engine was investigated in this study.  Inlet flow distortion was created by a layered wire mesh distortion screen designed to create a total pressure distortion profile at the aerodynamic interface plane (AIP) similar to NASA's Inlet A boundary layer ingesting inlet flow profile.  Results of this investigation showed a 15.5% decrease in stream thrust and a 14% increase in TSFC in the presence of BLI-type distortion. Flow measurements at the AIP and the bypass nozzle exit plane provided information about the losses throughout the fan flow path.  The presence of the distortion screen resulted in a 24% increase in mass-averaged entropy production along the entire fan flow path compared to the non-distorted test.  A mass-averaged fan flow path efficiency was also calculated assuming an isentropic process as ideal.  The non-distorted fan flow path efficiency was computed to be 60%, while the distorted fan flow path efficiency was computed to be 50.5%, a reduction in efficiency of 9.5%.  The entropy generation between ambient conditions and the AIP was compared to the entropy production along the entire fan flow path.  It was found that the majority of entropy generation occurred between the AIP and bypass nozzle exit.  Based on flow measurements at the bypass nozzle exit plane, it was concluded that inlet flow distortion should be located away from the tip region of the fan in order to minimize losses in a very lossy region.  It was also determined that the fan and bypass duct process the different regions of the total pressure distortion in different ways.  In some regions the entropy production decreased for the distorted test compared to the clean test, while in other regions the entropy production increased for the distorted test compared to the clean test.  Finally, it was found that small improvements in total pressure and total temperature variation at the bypass nozzle exit plane will greatly improve the fan flow path efficiency and entropy generation, thereby decreasing performance losses. / Master of Science

Highly integrated airframe-propulsion systems featuring ingestion of the airframe boundary layer offer reduced noise, emissions, and fuel consumption. Embedded engine systems are envisioned which require boundary layer ingesting (BLI) serpentine inlets to provide the needed air ow to the engine. These inlets produce distorted flow profiles that can cause aeromechanical, stability, and performance changes in embedded engines. Proper design of embedded engine systems requires understanding of the underlying fluid dynamics that occur within serpentine inlets. A serpentine inlet was tested in a specially designed wind tunnel that simulated boundary layer ingestion in a full-scale realistic environment. The measured total pressure proles at the inlet and exit planes of the duct, and the static pressure distributions along the walls provided useful data related to the flow in BLI serpentine inlet systems. A bleed ow control system was tested that utilized no more than 2% of the total inlet ow. Two bleed slots were employed, one near the first bend of the S-duct and one near second. The bleed system successfully reduced inlet distortions by as much as 30%, implying improvements in stall margin and engine performance. Analysis of the wake shape entering the S-duct showed that the airframe and inlet duct are both important components of a wake-ingesting inlet/diffusion system. Shape effects and static pressure distributions determined flow transport within the serpentine inlet. Flow separation within the S-duct increased distortion at the engine inlet plane. Discussion of airframe/inlet/engine compatibility demonstrates that embedded engine systems require multi-disciplinary collaborative design efforts. An included fundamental analysis provides performance estimates and design guidelines. The ideal airframe performance improvement associated with wake-ingestion is estimated. / Master of Science

Yes / This paper presents an improved mathematical model for calculation of distortion vectors of two aligned surface meshes. The model shows better accuracy when benchmarked to an existing model with exceptional mathematical conditions, such as sharp corners and small radii. The model was implemented into a developed distortion compensation digital tool and applied to an industrial component. The component was made of Inconel 718 and produced by laser powder bed fusion 3D printing technology. The digital tool was utilised to compensate the original design geometry by pre-distortion of its original geometry using the developed mathematical model. The distortion of an industrial component was reduced from approximately ±400 µm to ±100 µm for a challenging thin structure subjected to buckling during the build process.