Sanford Fleeter

Bio: Sanford Fleeter is an academic researcher from Purdue University. The author has contributed to research in topics: Aerodynamics & Airfoil. The author has an hindex of 20, co-authored 321 publications receiving 1902 citations. Previous affiliations of Sanford Fleeter include General Motors.

Multi-Blade Row Interactions in a Transonic Axial Compressor: Part I — Stator Particle Image Velocimetry (PIV) Investigation

Abstract: Multi-blade row interactions in an advanced design 1&1/2 stage axial-flow compressor are experimentally investigated at both subsonic and transonic rotor operating conditions using particle image velocimetry (PIV). Transonic rotor operation had a significant impact on the downstream stator unsteady flow field due to phenomena associated with the intra-stator transport of the chopped rotor wake segments. In the stator reference frame, the rotor wakes have a slip velocity relative to the mean flow that causes the low momentum wake fluid to migrate across the vane passage and accumulate on the stator pressure surface as the chopped wake segments are transported downstream. This results in the generation of counter-rotating vortices on each side of the chopped wake segment that convect downstream with the mean flow and act as an additional source of unsteadiness to the vane pressure surface. These interaction phenomena are not evident in the PIV data at the part-speed compressor operating condition due to the much lower velocity deficit and hence slip velocity associated with the subsonic rotor wakes.Copyright © 2001 by ASME

Rotor blade pressure measurement in a high speed axial compressor using pressure and temperature sensitive paints

Abstract: Pressure and temperature sensitive paints have been utilized for the measurement of blade surface pressure and temperature distributions in a high speed axial compressor environment. Four blades were painted, two with temperature sensitive paints and two with pressure sensitive paints. This combination allows temperature distributions to be accounted for when determining the blade suction surface pressure distribution. Measurements were taken and pressure maps on the suction surface of a blade were obtained over a range of rotational speeds. The formation of a suction surface shock was detected at the higher speeds. Introduction Pressure and temperature sensitive paints (PSP and TSP) offer a unique and inexpensive means of determining surface pressure and temperature distributions. Continuous surface pressure and temperature distributions, impossible to obtain using conventional measurement techniques, are critical for understanding complex flow mechanism and allow direct comparisons with results from computational fluid dynamic calculations (CFD). Cost for a PSP/TSP measurement system can be justified when one considers the cost of a single permanently installed pressure f Postdoctoral Research Assistant, Member AIAA * Graduate Research Assistant, Student Member AIAA t Professor, Member AIAA Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All Right Reserved. transducer. Not only is the cost of installing these conventional probes an issue, but the aerodynamics and structural dynamics of the model can be seriously altered by modifications to accommodate the transducers and static pressure taps. Data rates for PSP and TSP are several orders of magnitude faster than data rates for conventional techniques. The theory and applications of PSP and TSP techniques are detailed in the later sections. Aerodynamic loads on turbomachine blade rows result in fatigue failure of rotating components. Increased fatigue life of all internal components would lead to reduced costs incurred by the owner. Hence, advancement in the fundamental understanding of blade surface pressure distribution will lead to improved designs and reduced costs in both development and maintenance of a gas turbine engine. Pressure measurements obtained with pressure sensitive paints will provide not only the variations in pressure on the whole blade surface, but will provide a large data base of pressure data which will be useful in development of advanced forced response models for use in turbomachine design. Recently, PSP measurements on rotating machinery were conducted by Burns and Sullivan [1.] with a laser-PMT based system. They obtained pressure distributions on a small wooden propeller and a TRW Hartzell propeller. Their PSP-derived pressure distributions across the blades show reasonable trends. In this study, the PSP and TSP techniques are further used to measure pressure and temperature distributions on rotor blades in a high speed axial compressor. Axial Compressor Facility The Purdue Research Axial Fan Facility features a 30.48 cm (12 in.) diameter, 2/3 hubtip ratio compressor rotor which is integral with the shaft. The drive system consists of a 400 horsepower AC motor driving a magnetic clutch with a variable speed output that drives a gearbox, as shown in Figure 1. Eighteen inlet guide vanes are twisted to produce a free vortex whirl into a 19 blade axial flow rotor. Both the inlet guide vanes and the rotor blades are designed with NACA 65 series airfoil sections on circular arc meanlines. The aluminum rotor blades have 2 in. chord and 2 in. span from the hub to tip. Located downstream of the rotor are eight aerodynamic struts that support the rotor bearing housing. Axial spacing between the trailing edge of the rotor and the leading edge of one of the struts nondimensionalized by the rotor chord CR is L/CR = 3.47. For these experiments, axial IGV-to-rotor spacing to chord ratio is set at Z/CR = 0.6 (10° IGV stagger angle). Note that the selection of rotor speeds is dictated by th&vibrational level of the machine. The velocity measurements have been made using hot-film sensors between the IGV and rotors. Typical spanwise distrtbjjjfions of relative Mach numbers and absolute flow angles at 14,750 rpm are shown in Fig, 2 (a) and (b), where %U/CR is the relative upstream distance from the rotors. A detailed discussion about hot-film measurements in the compressor is given by Johnston and Fleeter [2], PSP and TSP Theory and Measurement Techniques The physical processes involved in behavior of PSP and TSP have been thoroughly presented in literature [3-11], but will be covered briefly in this section for completeness. A probe molecule embedded in a polymer^ binder is elevated to an excited state by absorbing light of a particular wavelength. The molecule will return to the ground state by releasing the excitation energy. Energy can be dissipated via emission of light (fluorescence and phosphorescence) or through radiation less deactivation processes such as oxygen quenching and thermal quenching. For pressure sensitive paints (PSPs), the excess energy can be absorbed by oxygen molecules through a process in which energy is transferred to oxygen molecules in a collisional manner. This process, known as oxygen quenching, depends upon the concentration of oxygen molecules. Since the concentration of oxygen molecules is proportional to the partial pressure of oxygen, luminescence is sensitive to pressure due to the oxygen quenching process and can be modeled with the Stern-Volmer relation:

Rotating Stall Acoustic Signature in a Low-Speed Centrifugal Compressor: Part 1—Vaneless Diffuser

Abstract: An experimental study is performed to identify spatially coherent pressure waves, which would serve as precursors to the development of an instability in the Purdue Low-Speed Centrifugal Research Compressor when configured with a vaneless diffuser. To achieve this, sensitive electret microphones were uniformly distributed around the circumference in the inlet and diffuser sections of the compressor. Fourier analysis of simultaneously sampled data from these microphone arrays was employed to identify the development of dominant spatial modes in the pressure field in the compressor. The transition to stall was observed to be a gradual process, with the growth of the pressure waves into those corresponding to a large-scale stall condition occurring over a time span of 26 impeller revolutions. The excitation of the pressure waves, as indicated by spatial Fourier analysis, occurred 14 impeller revolutions before small changes were evident in the microphone signals, and 26 revolutions before the stall condition could be considered fully developed

Shunted piezoelectrics for passive control of turbomachine blading flow-induced vibrations

Abstract: The application of shunted piezoelectric elements to provide passive structural damping is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. An array of piezoelectric elements is bonded to an airfoil in the stator row. This airfoil is excited in a chordwise bending mode by the wakes generated by an upstream rotor. As the wakes drive the airfoil vibrations, the piezoelectrics experience a strain and in response produce an electric field. Tuned electrical circuits connected to the piezoelectrics as shunts dissipate this electrical energy, with multiple shunting techniques utilized. This electrical energy dissipation and the corresponding reduction in the airfoil mechanical energy result in a reduction in the magnitude of the resonant vibrations.

An Experimental Study of Vane Clocking Effects on Embedded Compressor Stage Performance

Abstract: Previous research has shown that vane clocking, the circumferential indexing of adjacent vane rows with similar vane counts, can be an effective means to increase stage performance, reduce discrete frequency noise, and/or reduce the unsteady blade forces that can lead to high cycle fatigue. The objective of this research was to experimentally investigate the effects of vane clocking in an embedded compressor stage, focusing on stage performance. Experiments were performed in the intermediate-speed Purdue three-stage compressor, which consists of an IGV followed by three stages. The IGV, Stator 1, and Stator 2 vane rows have identical vane counts, and the effects of vane clocking were studied on Stage 2. Much effort went into refining performance measurements to enable the detection of small changes in stage efficiency associated with vane clocking. At design loading, the change in stage efficiency between the maximum and minimum efficiency clocking configurations was 0.27 points. The maximum efficiency clocking configuration positioned the Stator 1 wake at the Stator 2 leading edge. This condition produced a shallower and thinner Stator 2 wake compared with the clocking configuration that located the wake in the middle of the Stator 2 passage. At high loading, the change in Stage 2 efficiency associated with vane clocking effects increased to 1.07 points; however, the maximum efficiency clocking configuration was the case where the Stator 1 wake passed through the middle of the downstream vane passage. Thus, impingement of the upstream vane wake on the downstream vane leading edge resulted in the best performance at design point but provided the lowest efficiency at an off-design condition.

A new controller architecture for high performance, robust, and fault-tolerant control

Abstract: We propose a new feedback controller architecture. The distinguished feature of our new controller architecture is that it shows structurally how the controller design for performance and robustness may be done separately which has the potential to overcome the conflict between performance and robustness in the traditional feedback framework. The controller architecture includes two parts: one part for performance and the other part for robustness. The controller architecture works in such a way that the feedback control system can be solely controlled by the performance controller when there is no model uncertainties and external disturbances and the robustification controller can only be active when there are model uncertainties or external disturbances.

A review of pressure-sensitive paint for high-speed and unsteady aerodynamics

Abstract: The current paper describes the development of pressure-sensitive paint (PSP) technology as an advanced measurement technique for unsteady flow fields and short-duration wind tunnels. Newly developed paint formulations have step response times approaching 1 μs, making them suitable for a wide range of unsteady testing. Developments in binder technology are discussed, which have resulted in new binder formulations such as anodized aluminium, thin-layer chromatography plate, polymer/ceramic, and poly(TMSP) PSP. The current paper also details modeling work done to describe the gas diffusion properties within the paint binder and understand the limitations of the paint response characteristics. Various dynamic calibration techniques for PSP are discussed, along with summaries of typical response times. A review of unsteady and high-speed PSP applications is presented, including experiments with shock tubes, hypersonic tunnels, unsteady delta wing aerodynamics, fluidic oscillator flows, Hartmann tube o...

Modeling and Analysis of Mistuned Bladed Disk Vibration: Status and Emerging Directions

Abstract: The literature on reduced-order modeling, simulation, and analysis of the vibration of bladed disks found in gas-turbine engines is reviewed. Applications to system identification and design are also considered. In selectively surveying the literature, an emphasis is placed on key developments in the last decade that have enabled better prediction and understanding of the forced response of mistuned bladed disks, especially with respect to assessing and mitigating the harmful impact of mistuning on blade vibration, stress increases, and attendant high cycle fatigue. Important developments and emerging directions in this research area are highlighted.

Flutter and Resonant Vibration Characteristics of Engine Blades

Abstract: This paper presents an in-depth study of blade vibration problems that seriously impact development of advanced gas turbine configurations. The motivation for this study arises from the author's conviction that structural integrity of power plants is the dominant factor that influences the quality, reliability, and marketability of the product. Implications of this study in the context of potential R&D challenges and opportunities of interest to industry, governments, and academia are discussed.