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

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...

https://journals.sagepub.com/doi/pdf/10.1243/09544100JAERO243

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

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.

/pdf/modeling-and-analysis-of-mistuned-bladed-disk-vibration-380rrehfek.pdf

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

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.

Flutter and Resonant Vibration Characteristics of Engine Blades

Applications of the unsteady vortex-lattice method in aircraft aeroelasticity and flight dynamics

Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the torsion mode unsteady aerodynamics of a biconvex airfoil cascade at realistic values of the reduced frequency for all interblade phase angles at a specified mean flow condition. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized in which only one airfoil in the cascade is oscillated at a time and the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at a specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillation cascade data are correlated with data obtained in this cascade with all airfoils oscillating at several interblade phase angle values. The influence coefficients are then utilized to determine the unsteady aerodynamics of the cascade for all interblade phase angles, with these unique data subsequently correlated with predictions from a linearized unsteady cascade model.

Investigation of oscillating cascade aerodynamics by an experimental influence coefficient technique

Linear theory unsteady aerodynamics - Stator row response to combined vortical/potential forcing functions

HCF of turbomachinery blading is a significant design problem because fatigue failures can result from resonant vibratory stresses sustained over a relatively short time. Fatigue failure result from a combination of steady stress, vibratory stress, and material imperfections. However, the size of microscopic imperfections is difficult to control. Hence, stress-range diagrams are used to quantify the allowable vibratory stress amplitudes to avoid fatigue damage. Advanced turbomachinery blading is designed to have high steady stress levels. Thus, HCF occurs because of high mean stress low amplitude vibratory loading of the airfoils. The prediction of the vibratory stress level for input to the stress-range diagram requires the analysis of the blade row unsteady aerodynamics, structural characteristics, and resonant vibration response. This is because the root cause of the vibratory stress is flowinduced vibrations. Introduction High cycle fatigue (HCF) resulting in the loss of gas turbine engine blades or disks is currently the predominant surprise engine failure mode after the completion of engine development. This is a direct result of the introduction of high thrust-to-weight ratio engines, accomplished by increasing the mass flow and utilizing fewer parts. The required compressor designs featured fewer stages comprised of closely spaced rows of thin low aspect ratio balding with high tip speeds. The increased mass flow then results in a significant increase in the aerodynamic loading and the steady state stress. Also, the mechanical damping is considerably reduced in newer rotor designs. As a result, the low aspect ratio balding of advanced high thrust-to-weight ratio engines have experienced unexpected reliability issues, with HCF of particular concern. HCF is metal fatigue that results from cracking or fracture phenomenon generally characterized by the failure of small cracks at stress levels substantially lower than stresses associated with steady loading. Namely, HCF results from a combination of steady stress, vibratory stress, and material imperfections. It is initiated by the formation of a small, often microscopic, crack. The vibratory stress levels required to produce a fatigue crack at a specific mean stress level are then determined from stress-range diagrams, Figure 1.

/pdf/fatigue-life-prediction-of-turbomachine-blading-24lc95jbkx.pdf

Fatigue Life Prediction of Turbomachine Blading

Turbomachine discrete frequency tones are a signi® cant environmental concern. These tones are generated by periodic blade row interactions, with only speci® c circumferential acoustic modes generated. This research is directed at active control of discrete frequency noise generated by subsonic blade rows through cancellation of the propagating acoustic waves, accomplished by utilizing airfoil surface mounted oscillating actuators to generate additional control propagating pressure waves. These control waves interact with the propagating acoustic waves, thereby canceling the acoustic waves and thus the far-® eld discrete frequency tones. A series of experiments are described, directed at investigating the fundamentals of this active discrete frequency noise control technique as well as verifying basic modeling assumptions. Both an isolated vane and a three-vane row are utilized, with the

Active Control of Turbomachine Discrete Frequency Noise Utilizing Oscillating Flaps and Pistons

Results are presented from an experiment designed to actively suppress a rotating stall condition in a low speed centrifugal compressor. The control system uses a circumferential array of twelve air injection jets located in the endwall of the compressor inlet. The system is able to suppress the eruption of a one-cell rotating stall condition in the compressor during stall initiation, but the eruption of high order stall conditions limits stable operating range extension. The controller is also capable of destabilizing the compressor and accelerating the eruption of the first spatial mode.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Sanford Fleeter

Papers

Investigation of oscillating cascade aerodynamics by an experimental influence coefficient technique

Linear theory unsteady aerodynamics - Stator row response to combined vortical/potential forcing functions

Fatigue Life Prediction of Turbomachine Blading

Active Control of Turbomachine Discrete Frequency Noise Utilizing Oscillating Flaps and Pistons

Active control of rotating stall in a low-speed centrifugal compressor