With the advent of smart materials it is becoming possible to alter the structural characteristics of turbomachine airfoils. This change in structural characteristics can include, but is not limited to, changes in the shape (morphing) of the airfoil. Through changes in the airfoil shape, aerodynamic performance can be improved. Moreover, this technique has the potential to act as a flutter suppressant. In this investigation changes in the airfoil front camber while maintaining the airfoil thickness distribution are made to increase airfoil stability. The airfoil section is representative of current low aspect ratio fan blade tip sections. To assess the influence of the change in airfoil shape on stability the work-per-cycle was evaluated for torsion mode oscillations around the mid-chord at an inlet Mach number of 0.5 with an interblade phase angle of 180 degree Cchordal incidence angles of both 0 degree and 10 degree, and a reduced frequency of 0.4.

Inlet total pressure non-uniformities in axial flow fans and compressors can contribute to the loss of component structural integrity through high cycle fatigue (HCF) induced by the excitation of blade vibratory modes. As previous research has shown total pressure distortion to be the dominant HCF driver in aero engines [Manwaring et al, 1997], an understanding of its transfer through, and impact on, subsequent turbomachine stages and engine components is an important topic for assessment. Since current modeling techniques allow for total pressure distortion magnitudes to be directly related to blade vibratory response, the prediction of downstream distortion patterns from an upstream measurement would allow for the inference of the vibratory response of downstream blade rows to an inlet total pressure distortion. Nonlinear Volterra theory can be used to model any periodic nonlinear system as an infinite sum of multidimensional convolution integrals. A semi-empirical model has been developed using this theory by assuming that a distortion waveform is a periodic signal that is being presented to a nonlinear system, the compressor being the system. The use of Volterra theory in nonlinear system modeling relies on the proper identification of the Volterra kernels, which make up the transfer function that defines the system's impulse response characteristics. Once the kernels of a system are properly identified, the system's response can be calculated for any arbitrary input. This model extracts these kernels from upstream and downstream total pressure distortion measurements of a transonic rotor of modern design. The resulting transfer function is then applied to predict distortion transfer at new operating points on the same rotor and compared with the measured data. The judicious choice of distortion measurement data allows predictions of the downstream distortion content based on a measured non-uniform inlet flow at conditions different from those at which the transfer function was derived. This allows for the determination of downstream total pressure distortion that has the potential to excite blade vibratory modes that could lead to HCF under operating conditions other than those at which the data was taken, such as varying inlet distortion patterns, mass flow settings, rotational speeds, and inlet geometry. This report presents the creation of a Volterra model in order to predict distortion transfer in axial flow fans and compressors. This model, in three variations, is applied to a variety of distortions and compressor operating conditions as measured in the ADLARF tests at the Compressor Research Facility. Predictions are compared with data from the test and final results are also compared with two previous studies conducted at Virginia Tech using the same experimental data. Using the Volterra model it is shown that, with appropriate limitations, distortion transfer can be predicted for flow conditions different from those used for calibration. The model is considered useful for both performance and HCF investigations. / Master of Science

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The research effort presented in this dissertation consists of employing active trailing edge blowing control to reduce the unsteady stator-rotor interaction in a turbofan simulator. Two active flow control systems with different wake sensing approaches are successfully implemented on the engine simulator. The first flow control system utilizes Pitot probes as flow sensors. Use of Pitot probes as sensors is appropriate as a first step toward a more in depth investigation of active trailing edge blowing control. An upper performance limit in terms of wake-filling can be obtained and serves as the baseline in evaluating other control systems with indirect wake sensors. The ability of the system to achieve effective wake filling when subjected to a change in inlet flow conditions demonstrates the feasibility and advantage of active flow control. Significant tonal noise reductions in the far field are also obtained. The second control system involves using microphones as indirect wake sensors. The significance of these acoustic sensing approaches is to provide a practical TEB approach for realistic engines implementations. Microphones are flush mounted on the inlet case to sense the tonal noise at the blade passing frequency. The first sensing approach only uses the tone magnitude while the second novel sensing approach utilizes both the tone magnitude and phase as error information. The convergence rate of the second sensing approach is comparable with that of the Pitot-probe based experiments. The acoustic results obtained from both sensing approaches agree well with those obtained using Pitot probes as sensors. In addition to the experimental part of this research, analytical studies are also conducted on the trailing edge blowing modeling using an aeroacoustic code. An analytical model for trailing edge blowing is first proposed. This model is then introduced into the two-dimensional aeroacoustic code to investigate effect of various trailing edge blowing managements in the tonal sound generation. / Ph. D.

The largest single cause of failure in fan and compressor components in the cold frontal sections of commercial and military gas turbine engines has been attributed to high cycle fatigue (HCF). Additionally, both high-cycle fatigue (HCF) and lowcycle fatigue (LCF) loadings are widely recognized as unavoidable during operation of these components and because the classic Linear Damage Rule (LDR) neglects to account for the synergistic interaction between these damage contributors, dangerous over predictions of lifetime can result. Combined low-cycle fatigue / high-cycle fatigue (HCF/LCF) loadings were investigated in smooth Ti-6Al-4V. The specimens were subjected to a variable amplitude block loading history comprised of completely-reversed (R = -1) tensioncompression overloads followed by constant-amplitude zero-tension (R = 0) minor cycles. Axial specimens were excised from forgings representative of turbine engine fan blade forgings, and consisted of approximately 60% primary α in a matrix of lamellar α + β. Data are reported for smooth specimens of Ti-6Al-4V subjected to both constant amplitude and variable amplitude loadings. The axial specimens were prepared according to two distinct specimen conditions: low stress ground and longitudinallypolished (LSG+LP) and stress-relieved and chemically milled (SR+CM) conditions. Significantly longer lives were observed for the LSG+LP specimen condition under both constant and variable amplitude loading, due to the presence of a beneficial compressive surface residual stress. The presence of this residual stress was confirmed by x-ray diffraction, and its magnitude was of the order of 180 MPa (~20% of the yield stress). In either specimen condition, no appreciable effect of periodic overloads on the life of subsequent minor cycles was observed. / Master of Science

<p>Two state of the art finite element reduction techniquespreviously validated against the direct finite element method,one based on classical modal analysis and another based oncomponent mode synthesis, are applied for efficient mistunedfree vibration and forced response analysis of several bladeddisk geometries. The methods are first applied to two testcases in order to demonstrate the differences in computationalefficiency as well as to validate the methods againstexperimental data. As previous studies have indicated, nonoticeable differences in accuracy are detected for the currentapplications, while the method based on classical modalanalysis is significantly more efficient. Experimental data(mistuned frequencies and mode shapes) available for one of thetwo test cases are compared with numerical predictions, and agood match is obtained, which adds to the previous validationof the methods (against the direct finite element method).</p><p>The influence of blade-to-blade coupling and rotation speedon the sensitivity of bladed disks to mistuning is thenstudied. A transonic fan is considered with part span shroudsand without shrouds, respectively, constituting a high and alow blade-to-blade coupling case. For both cases, computationsare performed at rest as well as at various rotation speeds.Mistuning sensitivity is modelled as the dependence ofamplitude magnification on the standard deviation of bladestiffnesses. The finite element reduction technique based onclassical modal analysis is employed for the structuralanalysis. This reduced order model is solved for sets of randomblade stiffnesses with various standard deviations, i.e. MonteCarlo simulations. In order to reduce the sample size, thestatistical data is fitted to a Weibull (type III) parametermodel. Three different parameter estimation techniques areapplied and compared. The key role of blade-to-blade coupling,as well as the ratio of mistuning to coupling, is demonstratedfor the two cases. It is observed that mistuning sensitivityvaries significantly with rotation speed for both fans due toan associated variation in blade-to-blade coupling strength.Focusing on the effect of one specific engine order on themistuned response of the first bending modes, it is observedthat the mistuning sensitivity behaviour of the fan withoutshrouds is unaffected by rotation at its resonant condition,due to insignificant changes in coupling strength at thisspeed. The fan with shrouds, on the other hand, shows asignificantly different behaviour at rest and resonant speed,due to increased coupling under rotation. Comparing the twocases at resonant rotor speeds, the fan without shrouds is lessor equally sensitive to mistuning than the fan with shrouds inthe entire range of mistuning strengths considered.</p><p>This thesis’scientific contribution centres on themistuning sensitivity study, where the effects of shrouds androtation speed are quantified for realistic bladed diskgeometries. However, also the validation of two finite elementreduction techniques against experimental measurementsconstitutes an important contribution.</p>

The work presents the research of high-strength cast iron used for manufacturing of large grinding structures with dross layer and with non-homogeneous heat treatment volumes that remains inside during manufacturing process and subjected to high-cycle loading. The original research methodology used for investigations allowed to obtain the results of high-cycle loading. Obtained results have been used to improve the structural elements calculation methods.

The work presents the research of high-strength cast iron used for manufacturing of large grinding structures with dross layer and with non-homogeneous heat treatment volumes that remains inside during manufacturing process and subjected to high-cycle loading. The original research methodology used for investigations allowed to obtain the results of high-cycle loading. Obtained results have been used to improve the structural elements calculation methods.

An accelerated high cycle fatigue testing approach is presented to determine the fatigue endurance limit of materials at high frequencies. Base excitation of a tapered plaque driven into a high frequency resonance mode allows the test to be completed in a significantly shorter time. This high cycle fatigue testing is performed using the tracked sine resonance search and dwell strategy. The controller monitors the structural health during the test. Any change in the dynamic response indicates crack initiation in the material. In addition, a shape optimization finite element model is conducted for the design of the tapered plaques. An integrated neural (Neural-Network) genetic (NSGA_II) optimization technique is implemented to carry out the shape optimization for this component. This process results in a significant reduction in the computational cost. A Pareto set is then produced that meets the designer&rsquo;s requirements and provides the decision maker several alternatives to choose from.