The interaction between a high-frequency gust and a blade row

1992 ◽  
Vol 241 ◽  
pp. 261-289 ◽  
Author(s):  
N. Peake
Keyword(s):  
Flat Plates ◽  
Rotating Blade ◽  
Reduced Frequency ◽  
Blade Row ◽  
Method Of Solution ◽  
Physical Insight ◽  
Formal Limit ◽  
Underlying Mechanisms ◽  
High Level ◽  
Unsteady Lift

The ingestion of convected vorticity by a high-solidity rotating blade row is a potent noise source in modern aeroengines, due largely to the high level of mutual aerodynamic interactions between adjacent blades. In order to model this process we solve the problem of determining the unsteady lift on an infinite cascade of finite-chord flat plates due to an incident vorticity wave. The method of solution is the Wiener–Hopf technique, and we consider the case of the reduced frequency, Ω, being large, allowing application of asymptotic analysis in the formal limit Ω → ∞. This approach yields considerable simplification, both in allowing the truncation of an infinite reflection series to just two terms, and in allowing algebraic expressions for the Wiener–Hopf split functions to be found. The unsteady lift distribution is derived in closed form, and the accuracy of the asymptotic Wiener–Hopf factorization demonstrated for even modest values of Ω by comparison with exact (but less tractable) methods. Our formulae can easily be incorporated into existing noise prediction codes: the advantage of our scheme is that it handles a regime in which conventional numerical approaches become unwieldy, as well as providing significant physical insight into the underlying mechanisms.

A uniform asymptotic approximation for high-frequency unsteady cascade flow

1995 ◽  
Vol 449 (1935) ◽  
pp. 177-186 ◽  
Keyword(s):  
High Frequency ◽  
Asymptotic Approximation ◽  
Model Problem ◽  
Noise Generation ◽  
Flat Plates ◽  
Infinite Products ◽  
Cascade Flow ◽  
Reduced Frequency ◽  
Physical Insight ◽  
Exact Factorization

The scattering of harmonic gusts by a two-dimensional, infinite cascade of flat plates is a model problem which is relevant to the prediction of noise generation by rotating turbomachinery. The problem can be solved analytically using the Wiener‒Hopf technique, and the key step involves the exact factorization of a certain generic kernel function, K , using infinite products. An approximate fac­torization, based on the realistic asymptotic limit of large reduced frequency, has been derived by Peake, and this approach has the advantages of both providing more physical insight and being significantly easier to compute than the exact factors. An important limitation of Peake’s approximation, however, is that it be­ comes invalid when any of the acoustic modes in the system are close to cut-off, and in this paper we therefore present new asymptotic factors which overcome this non-uniformity. The accuracy of this new approximation, across a whole range of operating parameters, is demonstrated by comparison with the exact results, with typical errors of the order of only 3% even for very modest values of the reduced frequency.

The Unsteady Response of a Blade Row From Measurements of the Time-Mean Total Pressure

1973 ◽  
Author(s):  
R. E. Henderson
Keyword(s):  
Experimental Data ◽  
Theoretical Analysis ◽  
Total Pressure ◽  
Theoretical Data ◽  
Two Dimensional ◽  
Interference Effects ◽  
Experimental Procedure ◽  
Rotating Blade ◽  
Reduced Frequency ◽  
Blade Row

An experimental procedure is described which permits the unsteady response of a rotating blade row to spatial variations in its inlet flow to be determined from measurements of the time-mean total pressure. This procedure has been employed to determine the unsteady circulation of a non-lifting rotor as a function of reduced frequency for two values of space-chord ratio. Comparisons of these experimental data are made with a recent theoretical analysis of the indirect or design problem of unsteady lift in a moving two-dimensional cascade. Both the experimental and theoretical data are shown to exhibit the same trends with variations in space-chord ratio and reduced frequency. These results demonstrate that the unsteady blade interference effects are significant, and that the representation of the unsteady response of a turbomachine blade row as an isolated airfoil is not valid for reduced frequencies less than 1.2.

Access Control Models for Online Social Networks

2014 ◽  
pp. 451-484
Author(s):  
Rula Sayaf ◽  
Dave Clarke
Keyword(s):  
Social Networks ◽  
Access Control ◽  
Online Social Networks ◽  
Personal Data ◽  
Security And Privacy ◽  
Open Problems ◽  
Access Control Models ◽  
Control Models ◽  
Underlying Mechanisms ◽  
High Level

Access control is one of the crucial aspects in information systems security. Authorizing access to resources is a fundamental process to limit potential privacy violations and protect users. The nature of personal data in online social networks (OSNs) requires a high-level of security and privacy protection. Recently, OSN-specific access control models (ACMs) have been proposed to address the particular structure, functionality and the underlying privacy issues of OSNs. In this survey chapter, the essential aspects of access control and review the fundamental classical ACMs are introduced. The specific OSNs features and review the main categories of OSN-specific ACMs are highlighted. Within each category, the most prominent ACMs and their underlying mechanisms that contribute enhancing privacy of OSNs are surveyed. Toward the end, more advanced issues of access control in OSNs are discussed. Throughout the discussion, different models and highlight open problems are contrasted. Based on these problems, the chapter is concluded by proposing requirements for future ACMs.

SEARCHING AND MINING VISUALLY OBSERVED PHENOTYPES OF MAIZE MUTANTS

2007 ◽  
Vol 05 (06) ◽  
pp. 1193-1213 ◽  
Author(s):  
CHI-REN SHYU ◽  
JATURON HARNSOMBURANA ◽  
JASON GREEN ◽  
ADRIAN S. BARB ◽  
TONI KAZIC ◽  
...  
Keyword(s):  
Cell Biology ◽  
Species Conservation ◽  
Genetic Maps ◽  
Cell Physiology ◽  
Complex Processes ◽  
Intimate Knowledge ◽  
Scientific Challenge ◽  
Underlying Mechanisms ◽  
Mutant Phenotypes ◽  
High Level

There are thousands of maize mutants, which are invaluable resources for plant research. Geneticists use them to study underlying mechanisms of biochemistry, cell biology, cell development, and cell physiology. To streamline the understanding of such complex processes, researchers need the most current versions of genetic and physical maps, tools with the ability to recognize novel phenotypes or classify known phenotypes, and an intimate knowledge of the biochemical processes generating physiological and phenotypic effects. They must also know how all of these factors change and differ among species, diverse alleles, germplasms, and environmental conditions. While there are robust databases, such as MaizeGDB, for some of these types of raw data, other crucial components are missing. Moreover, the management of visually observed mutant phenotypes is still in its infant stage, let alone the complex query methods that can draw upon high-level and aggregated information to answer the questions of geneticists. In this paper, we address the scientific challenge and propose to develop a robust framework for managing the knowledge of visually observed phenotypes, mining the correlation of visual characteristics with genetic maps, and discovering the knowledge relating to cross-species conservation of visual and genetic patterns. The ultimate goal of this research is to allow a geneticist to submit phenotypic and genomic information on a mutant to a knowledge base and ask, "What genes or environmental factors cause this visually observed phenotype?".

About Transonic Compressor Tandem Design: A Principle Study

2015 ◽  
Author(s):  
A. Hergt ◽  
U. Siller
Keyword(s):  
Industrial Application ◽  
Design Space ◽  
Research Work ◽  
Design Principles ◽  
Compressor Blade ◽  
Tandem Arrangement ◽  
Axial Compressors ◽  
Transonic Compressor ◽  
Blade Row ◽  
High Level

The development of modern axial compressors has already reached a high level. Therefore an enlargement of the design space by means of new or advanced aerodynamic methods is necessary in order to achieve further enhancements of performance and efficiency. The tandem arrangement of profiles in a transonic compressor blade row is such a method. For an efficient industrial application the knowledge of the fundamental design principles is needed. This paper presents the recent research work on transonic compressor tandem profiles at DLR Institute of Propulsion Technology. It deals with the fundamental description of the operation principles of a modern transonic compressor tandem cascade. By considering these principles and based on an optimization database with over 1200 members design recommendations are developed.

Fuzzy Model for Human Color Perception and Its Application in E-Commerce

2016 ◽  
Vol 24 (Suppl. 2) ◽  
pp. 47-70 ◽  
Author(s):  
Pakizar Shamoi ◽  
Atsushi Inoue ◽  
Hiroharu Kawanaka
Keyword(s):  
Image Retrieval ◽  
Color Perception ◽  
Fuzzy Model ◽  
Visual Features ◽  
Perceptual Categorization ◽  
Purchasing Behavior ◽  
User Query ◽  
Hsi Space ◽  
Underlying Mechanisms ◽  
High Level

Although image retrieval for e-commerce field has a huge commercial potential, e-commerce oriented content-based image retrieval is still very raw. Modern online shopping systems have certain limitations. In particular, they use conventional tag-based retrieval and lack making use of visual content. The paper presents a methodology to retrieve images of shopping items based on fuzzy dominant colors. People regard color as an aesthetic issue, especially when it comes to choosing the colors of their clothing, apartment design and other objects around. No doubt, color inuences purchasing behavior — to a certain extent, it is a reection of human's likes and dislikes. The fuzzy color model that we are proposing represents the collection of fuzzy sets, providing the conceptual quantization of crisp HSI space having soft boundaries. The proposed method has two parts: assigning a fuzzy colorimetric profile to the image and processing the user query. We also use underlying mechanisms of attention from a theory of visual attention, like perceptual categorization. Subjectivity and sensitivity of humans in color perception and bridging the semantic gap between low-level color visual features and high-level concepts are major issues that we plan to tackle in this research.

Influence of mean loading on noise generated by the interaction of gusts with a flat-plate cascade: upstream radiation

1997 ◽  
Vol 347 ◽  
pp. 315-346 ◽  
Author(s):  
N. PEAKE ◽  
E. J. KERSCHEN
Keyword(s):  
Incidence Angle ◽  
Outer Region ◽  
Leading Edge ◽  
Mean Flow ◽  
Flat Plates ◽  
Flow Distortion ◽  
Reduced Frequency ◽  
Flow Interactions ◽  
Source Mechanisms ◽  
Harmonic Components

The sound generated by the interaction between convected vortical and entropic disturbances and a blade row is a significant component of the total noise emitted by a modern aeroengine, and the blade geometry has an important effect on this process. As a first step in the development of a general prediction scheme, we model in this paper just the action of the blade mean loading by treating the blades as flat plates aligned at a non-zero incidence angle, δ, to the oncoming stream, and consider harmonic components of the incident field with reduced frequency k. We then use asymptotic analysis in the realistic limit k[Gt ]1, δ[Lt ]1 with kδ=O(1) to make a consistent asymptotic expansion of the compressible Euler equations. The flow is seen to consist of inner regions around each leading edge, in which sound is generated by the local gust–airfoil and gust–flow interactions, and an outer region in which both the incident gust is distorted according to rapid distortion theory and the out-going sound is refracted by the non-uniform mean flow. The complicated multiple interactions between the sound and the cascade are included to the appropriate asymptotic order, and analytical expressions for the forward radiation are derived. It is seen that even a relatively small value of δ can have a significant effect, thanks to both the O(δk1/2) change in the amplitudes and the O(kδ) change in the phases of the various radiation components, corresponding to the additional source mechanisms associated with the flow distortion around each leading edge and the effects of propagation through the non-uniform flow, respectively. Further work will extend this analysis to include the effects of camber and thickness.

Sign in / Sign up

Export Citation Format

Share Document