The effects of trailing edge flow control on the wakes of a linear cascade of idealized fan blades was investigated experiments with a view to the likely effects on broadband aircraft engine interaction noise. Single and three-component hotwire velocity measurements were made downstream of the cascade for a chord Reynolds number of 390,000 and a Mach number of 0.07. Measurements of the two-point velocity correlation were used extensively to evaluate the impact of various flow control strategies on the organization of the coherent structures of the wakes and their potential to generate noise. A baseline flow was established by measuring the wake downstream of unmodified GE-Rotor-B blades. Four sets of serrated trailing edge blades (with two different serration sizes and with two trailing edge cambers) and three sets of blades with trailing edge blowing (a simple rectangular slot, rectangular slot with Kuethe-vane vortex generators, and rectangular slot with serrated lips) were tested. The serrated trailing edges introduce corrugations into the wake, increase the wake decay and width as well as turbulence levels (possibly because of the blunt trailing edge created at the serration valley). The serrated trailing edges also increase the turbulence scales in the direction perpendicular to the plane of the wake because of the injection of streamwise vorticity. In almost all cases the serrations reduce the spanwise and streamwise turbulence scales. Serrations do not, however, affect the apparent time scale of quasi-periodic structures in the wake, and this appears to limit the potential of this trailing edge treatment to reduce broadband noise. The analysis of the characteristic eddies (obtained from proper orthogonal decomposition combined with linear estimation) revealed that the serrations do not change the qualitative form of the eddies. Trailing edge blowing was found to significantly decrease the wake deficit and width as well as the turbulence levels at all blowing rates. Blowing through the simple rectangular slot, at mass flow rates between 1.4 and 2.0% of the total passage through flow, was shown to significantly affect the size, the organization and the strength of the coherent structures. For small blowing rates the strong spanwise eddies near the trailing edge actually appear to be enhanced. For larger blowing rates, however, the turbulent scales are reduced in all directions. The addition of Kuethe vanes on the suction side of the blowing blade results in a low momentum region just downstream of the vanes that may result from flow separation there. This further enhances the shedding and increases the blowing rate needed to overcome it. The serrated blowing blades show the greatest potential to reduce broadband noise as they reduce the turbulence levels and scales without creating potentially detrimental structures. While no acoustic measurements were made, analysis of hypothetical perpendicular and parallel interactions of blades with these wakes has made possible to characterize for the first time the impact of the changes in the eddy structure of these wakes on their potential to generate broadband noise. The serrated trailing edges (especially the larger serrations) actually increase the potential of the wake to generate broadband noise (a direct consequence in the overall increase in turbulence scale and intensity). In contrast, every trailing edge blowing configuration was found to produce large reductions in the potential noise (a maximum of 6dB reduction was obtained at 2.0% blowing). The addition of Kuethe vanes on the suction side of the blowing blades significantly reduced the efficiency of the simple blowing configuration (a result of the increased coherency associated with the shedding of streamwise vorticity by the vanes). The serrated blowing configuration was found to yield reductions similar to the simple blowing configuration. / Ph. D.

A series of experiments were conducted in a F109 turbofan engine to investigate the unsteady wake profiles of an Inlet Guide Vane (IGV) at a typical spacing to the downstream fan at subsonic and transonic relative blade velocities. The sharp trailing-edge vanes were designed to produce a wake profile consistent with modern IGV. Time averaged baseline measurements were first performed with the IGV located upstream of the aerodynamic influence of the fan. Unsteady experiments were performed with an IGV-fan spacing of 0.43 fan chords. High-frequency on-vane pressure measurements showed strong peak-to-peak amplitudes at the blade passing frequency (BPF) of 4.7 psi at the transonic fan speeds. High-frequency total pressure measurements of the IGV wake were taken between the IGV and fan. Results showed that the total pressure loss coefficient of the time averaged IGV wake is reduced by 30% for the subsonic fan, and increased by a factor of 2 for the transonic fan compared to the baseline. Time resolved wake profiles for subsonic fan speeds show constructive and destructive interactions over each blade pass generated by the fan potential flow field. Time resolved wake profiles for the transonic fan speeds show that shock interactions with the IGV surface result in the wake shedding off of the vane at the BPF. Furthermore, the effectiveness of trailing edge blowing (TEB) flow control was investigated. TEB is the method of injecting air aft of the IGV to reduce the low pressure regions (deficits) in the viscous wakes shed by the vanes. Minimizing the IGV wakes reduces the forcing function on the downstream fan blades, thereby reducing high cycle fatigue. The TE span of the vane contains discrete holes at the axial centerline for TEB. Baseline results showed that TEB eliminates the IGV wake, while using only 0.03% of the total engine mass flow per IGV. TEB for the subsonic fan at the close spacing shows complete wake filling using the same mass flow as the baseline. TEB for the transonic fan shows a reduction of 68% in the total pressure loss coefficient, while requiring 2.5 times the mass flow as the baseline. / Ph. D.

An innovative application of existing technology is proposed for attenuating the effects of transient phenomena, such as rotor-stator and rotor-strut interactions, linked to noise and fatigue failure in turbomachinery environments. A computational study was designed to assess the potential of Passive Porosity Technology as a mechanism for alleviating interaction effects and radiated noise by reducing the fluctuating forces acting on the vane surfaces. The study involved a typical high bypass fan stator airfoil immersed in a subsonic free field and exposed to the effects of a transversely moving wake. Time histories of the primitive aerodynamic variables obtained from Computational Fluid Dynamics (CFD) calculations were input into an acoustic prediction code to estimate noise levels at a radial distance of ten chords from the stator airfoil. This procedure was performed on the solid airfoil to obtain a baseline, and on approximately fifty porous configurations in order to isolate those that would yield maximum noise reductions without compromising the aerodynamic performance of the stator. It was found that, for a single stator immersed in a subsonic flow field, communication between regions of high pressure differential - made possible by the use of passive porosity - tends to induce a time-dependent oscillatory pattern of small inflow-outflow regions near the stator leading edge (LE), which is well established before wake effects come into play. The oscillatory pattern starts at the LE, and travels downstream on both suction and pressure sides of the airfoil. The amplitude of the oscillations seemed to be proportional to the extension of the porous patch on the pressure side. Regardless of this effect, which may not have occurred if the airfoil were placed within a stator cascade, communication between regions of high pressure differential is necessary to significantly alter the noise radiation pattern of the stator airfoil. Whether those changes result in noise abatement or enhancement depends primarily on the placement and extension of the porous patches. For most viable configurations, porosity reduced loading noise but increased thickness noise. Variations in nominal porosity were of secondary importance. In general, the best aerodynamic performers (i.e., those configurations that were able to reduce unsteady lift without severely altering the lift and/or drag characteristics of the solid airfoil) were also the best acoustic performers. As a result of using passive surface porosity, overall peak radiated noise was reduced by approximately 1.0 dB. This reduction increased to about 2.5 dB when the effects of loading noise alone were considered. / Ph. D.

With the growing need to meet aggressive emissions targets in the aerospace industry in the coming decades, the electrification of propulsion systems has become an area of great research and commercial interest. In order to achieve full electrification of larger commercial aircraft, it is critical to improve power and energy densities of components within the propulsion system. The power densities of electric motors are steadily rising to meet this requirement. Among the various motor designs available, the high-speed radial flux permanent magnet motor is presented as an architecture capable of achieving high efficiencies and power densities. Increasing power densities, however, poses challenges for the thermal management system as higher losses need to be dissipated from a relatively small machine package. One of the failure modes specific to permanent magnet motors is the demagnetization of the magnets in the rotor at higher temperatures which leads to a loss in performance. Therefore it is critical that the thermal management system of the rotor must effectively dissipate the losses generated in the magnets and other components within the rotor. This thesis discusses the mechanical and thermal design of a 150 kW high-speed radial flux surface mounted permanent magnet motor for aerospace propulsion applications. The thesis first introduces the current landscape of aerospace electrification, focusing specifically on electric and hybrid propulsion architectures, currently available electric motors for aerospace propulsion, and ongoing aircraft electrification projects. A review is then provided of the current state-of-the-art in rotor cooling designs for high-speed speed radial flux motors for traction applications before introducing the design of the motor proposed in this thesis. The discussion of the mechanical design provides a high level overview of the design, manufacturing, and assembly of the stator and rotating assemblies while the thermal design provides a brief overview of the stator cooling design and a deep dive on the rotor cooling design. Computational Fluid Dynamics (CFD) is used along with the Taguchi method for robust design to optimize the rotor cooling design for minimizing the magnet temperatures. Analysis for the optimized rotor cooling discussed is provided before providing recommendations for future work. / Thesis / Master of Applied Science (MASc)

Magnetic bearings support turbomachinery by regulating their forces exerted in relation to the displacement of the machine supported. The regulating control system must be tuned for stable and safe operation of the rotor. The ultimate goal of this study is to determine the effects of changing controller gains on the behavior of the rotor during operation in its normal speed range with a known unbalance load. We also endeavor to confirm the model of the rotor supported the magnetic bearings, as an additional goal. We first investigate the modelling of rotors supported by magnetic bearings, including the model of the control system. We present a finite element model of a magnetic bearing supported rotor, and perform experiments to determine the characteristics of the control system which governs the magnetic forces on the rotor. The experimental control system characteristics confirm the expected characteristics from theory. With this knowledge, we perform simulations and experiments under the same forcing conditions to determine the accuracy of the model in predicting the experimental behavior of an unbalanced rotor. The model exhibits satisfactory ability in predicting the experimental behavior of the rotor under this loading. Our next step is to determine the effects of variation of proportional and integral controller gains on the behavior of the rotor. Both simulations and experiments show that an increase in the proportional controller gain results in an increase in the rotor’s first critical speed. An increase in the integral gain results in a small decrease in the location of the peak response speed in the speed range tested, while leaving the peak amplitude insignificantly changed. Again, simulations and experiments predict this result. We reach the following three conclusions from this study. First, the finite element model of the rotor/bearing system is a viable model for predicting the behavior of the experimental system. Second, tuning of the proportional gain shows a significant effect on the behavior of the rotor during unbalance loading across its speed range, due to considerable change in bearing stiffness caused by the tuning of this gain. Last, tuning of the integral gain has a small effect on the behavior of the rotor due to the change in bearing damping, too small to be considered significant. / Master of Science

Extensive disturbance rejection methods have been established for time-invariant systems. However, the development of these techniques has not focused on application to time-periodic systems in particular until recently. The filtered-X LMS algorithm is regarded as the best disturbance rejection technique for aperiodic systems by many, as has been proven in the acoustics industry for rejecting unwanted noise. Since this is essentially a feedforward approach, we might expect its performance to be good with respect to time-periodic systems in which the disturbance frequency is already known. The work presented in this thesis is an investigation of the performance of the filtered-X LMS algorithm for disturbance rejection in time-periodic systems. Two cases are examined: a generalized linear, time-periodic system and the helicopter rotor blade in forward flight. Results for the generalized system show that the filtered-X LMS algorithm does converge for time-periodic disturbance inputs and can produce very small errors. For the helicopter rotor blade system the algorithm is shown to produce very small errors, with a 96%, or 14 dB, reduction in error from the open-loop system. The filtered-X LMS disturbance rejection technique is shown to provide a successful means of rejecting timeperiodic disturbances for time-periodic systems. / Master of Science

The primary purpose of this thesis is to quantify the effects of RANS turbulence modeling on the resolution of free shear vortical flows. The simulation of aerodynamic wing-tip vortices is used as a test bed. The primary configuration is flow over an isolated finite wing with aspect ratio, , and Reynolds number, . Tip-vortex velocity profiles, vortex core and wake turbulence levels, and Reynolds stresses are compared with wind tunnel measurements. Three turbulence models for RANS closure are tested: the Lumley, Reece, and Rodi full Reynolds stress transport model and the Sparlart-Allmaras model with and without a proposed modification. The main finding is that simulations with the full Reynolds stress transport model show remarkable mean flow agreement in the vortex and wake due to the proper prediction of a laminar vortex core. Simulations with the Spalart-Allmaras model did not indicate a laminar core and predicted over-diffusion of the tip-vortex. Secondary investigations in this work include the study of wall boundary layer treatment and simulating the wake-age of an isolated rotorcraft in hover using a steady-state RANS solver. By comparing skin friction plots over the NACA 0012 airfoil, it is shown that wall functions are most effective in the trailing edge half of the airfoil, while high velocity gradient and curvature of the leading edge make them more vulnerable to discrepancies. The rotorcraft simulation uses the modified Spalart-Allmaras turbulence model and shows proper, qualitative, resolution of the interaction between the vortex sheet and the tip vortex. / Master of Science

On-blade hot wire anemometry measurements as well as far field sound measurements at several receiving angles have been previously made for a rotor partially embedded in a boundary layer. The inflow distortion effect on the rotor angle of attack distribution was determined directly from the on-blade measurements, and was found to minimally affect the angle of attack at the blade tips and lower the angle attack in the rotor disk plane as the radial location moves towards the hub. A narrow, sharp increase in angle of attack as the rotor blades approached the wall was also observed, indicating blade interaction with flow reversal. The haystacking pattern, or spectral humps that appear at multiples of the blade passage frequency, was studied for a wide range of advance ratios. At high advance ratios, evidence of vortex shedding from the blade trailing edges was observed. For low advance ratios, the haystacks narrowed, became more symmetric and increased in number. A method of determining the average acoustic signature of an eddy passage through a rotor was developed from time delay aligning multiple microphone signals and eddy passages detected using the continuous wavelet transform. It was found that the eddy passage signatures were similar to a cosine wave with a Gaussian window. It was also found that normalized timescales obtained directly from the eddy passage signatures remained somewhat constant with advance ratio, but increases slightly for fixed free stream velocities with increasing rotor RPM. For advance ratios less than 0.6, the eddy passage signatures were dominated by a tonal component due to rotor ingestion of misaligned flow caused by a boundary layer separation at the wall. This indicates that flow reversal known as the Pirouette Effect is interacting with the rotor blades. / Master of Science

Gas turbine engines provide thrust for aircraft engines and supply shaft power for various applications. They consist of three main components. That is, a compressor followed by a combustion chamber (burner) and a turbine. Both turbine and compressor components are either axial or centrifugal (radial) in design. The combustion chamber is stationary on the engine casing. The type of engine that is of interest here is the gas turbine auxiliary power unit (APU). A typical APU has a centrifugal compressor, burner and an axial turbine. APUs generate mechanical shaft power to drive equipments such as small generators and hydraulic pumps. In airplanes, they provide cabin pressurization and ventilation. They can also supply electrical power to certain airplane systems such as navigation. In comparison to thrust engines, APUs are usually much smaller in design. The purpose of this research was to investigate the possibility of combining the three components of an APU into a single centrifugal rotor. To do this, a set of equations were chosen that would describe the new turbomachinery cycle. They either were provided or derived using quasi-one-dimensional compressible flow equations. A MathCAD program developed for the analysis obtained best design points for various cases with the help of an optimizer called Model Center. These results were then compared to current machine specifications (gas turbine engine, gasoline and diesel generators). The result of interest was maximum specific power takeoff. The results showed high specific powers in the event there was no restriction to the material and did not exhaust at atmospheric pressure. This caused the rotor to become very large and have a disk thickness that was unrealistic. With the restrictions fully in place, they severely limited the performance of the rotor. Sample rotor shapes showed all of them to have unusual designs. They had a combination of unreasonable blade height variations and very large disk thicknesses. Indications from this study showed that the single radial rotor turbomachinery design might not be a good idea. Recommendations for continuation of research include secondary flow consideration, blade height constraints and extending the flow geometry to include the axial direction. / Master of Science

Swedish Hydropower Centre - SVC