Download or read book Reduction of Tonal Propeller Noise by Means of Uneven Blade Spacing written by Tae Young Kim and published by . This book was released on 2016 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study was conducted on the noise characteristics of four-bladed general aviation propellers with uneven blade spacing. The subscale propeller designs were inspired by the fourbladed McCauley propellers used on the Beechcraft King Air 350 series aircraft. The 4-inch diameter (1:22.5 scale) propellers were manufactured using high-resolution stereolithography and were powered by a high performance, radio controlled brushless electric motor. Acoustic measurements were taken with a 24-microphone array. The use of uneven blade spacing created additional tones over which the acoustic intensity was distributed. Large amounts of acoustic intensity were shifted into the lowest frequency tone (occuring at half of the blade passage frequency of the propeller with evenly spaced blades), resulting in reductions of A-weighted overall sound pressure levels of up to 5 dB for polar angles near 90°. These reduction are partly offset by increases in A-weighted overall sound pressure levels of up to 4 dB at polar angles less than 50°. Although the theory used to predict propeller noise does not show good agreement with experiments, it does show this trend of increasing noise at low polar angles. Since noise at low polar angles are weighted less in noise metrics such as flyover noise, the use of uneven blade spacing has potential for providing noise reduction without adding excessive complexity to propeller design.
Download or read book Propeller Noise at Low Tip Speeds written by David Brown and published by . This book was released on 1971 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study comprises an analytical and experimental investigation of the vortex noise generated by low-tip speed propellers. Initally, the treatment of the subject is focussed on an examination of the origins of broadband noise and the methods by which these can be analytically represented. Subsequent noise measurements on simple-design propellers indicate how the typical spectra in the Strouhal frequency range are significantly influenced by an extensive range of high order harmonics of the blade passage frequency, and a treatment of this harmonic content is included in this study report. The broadband and harmonic components of noise data, obtained from propellers with blade number and blade angle variations, have been analyzed in detail and noise prediction methods have been derived for each. It is postulated that the noise source mechanisms may be associated with unstable laminar flow separation (or transition) at the blade surfaces. The report also includes a set of graphical procedures by which both harmonic and random spectral details of the radiated noise can be calculated by tip Mach numbers in the range 0.2 to 0.6. (Author).
Download or read book A Method for Calculation of Free space Sound Pressures Near a Propeller in Flight Including Considerations of the Chordwise Blade Loading written by Charles E. Watkins and published by . This book was released on 1956 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: The general expressions of NACA Report 1198 for determining the sound-pressure field for a rotating propeller in uniform subsonic flight are reviewed for the case of a propeller with uniform chordwise forces. Consideration is given to effects of nonuniform chordwise and radial blade loading. Tabulated values of certain definite integrals that are involved in the calculation of a near-field propeller noise regardless of the form of the chordwise forces are presented. These tabulations cover a wide range of operating conditions and are useful for estimating propeller noise when either the concept of an effective radius or radial distributions of forces are considered. In order to illustrate their use, the tabulations are used in conjunction with the concept of an effective radius to make evaluations for some specific propellers. Results of these evaluations are presented and discussed.
Download or read book Some Design Philosophy for Reducing the Community Noise of Advanced Counter rotation Propellers written by and published by . This book was released on 1985 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effect of Front to rear Propeller Spacing on the Interaction Noise of a Model Counterrotation Propeller at Cruise Conditions written by and published by . This book was released on 1987 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effect of Front To Rear Propeller Spacing on the Interaction Noise at Cruise Conditions of a Model Counterrotation Propeller Having a Reduced Diameter Aft Propeller written by National Aeronautics and Space Adm Nasa and published by . This book was released on 2018-10-12 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of forward-to-aft propeller spacing on the interaction noise of a counterrotation propeller with reduced aft diameter was measured at cruise conditions. In general, the tones at 100 percent speed decreased from close to nominal spacing as expected from a wake decay model. However, when the spacing was further increased to the far position, the noise did not decrease as expected and in some cases increased. The behavior at the far spacing was attributed to changing forward propeller performance, which produced larger wakes. The results of this experiment indicate that simple wake decay model is sufficient to describe the behavior of the interaction noise only if the aerodynamic coupling of the two propellers does not change with spacing. If significant coupling occurs such that the loading of the forward propeller is altered, the interaction noise does not necessarily decrease with larger forward-to-aft propeller spacing. Dittmar, James H. and Gordon, Eliott B. and Jeracki, Robert J. Glenn Research Center RTOP 535-03-01...
Download or read book A Propeller Skew Optimization Method written by and published by . This book was released on 1987 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: A propeller operating in the turbulent wake of an axisymmetric body with appendages encounters wake non-uniformities which result in spatial and temporal fluctuations of blade angle-of-attack. These angle-of-attack fluctuations result in unsteady blade loadings and the generation of propeller noise, and the noise sources are characterized by three types of unsteady force mechanisms: a) turbulence injestion; b) vortex shedding; and c) blade-rate. The first two mechanisms typically generate continuous spectrum (broadband) radiated noise levels while blade-rate forces generate discrete frequency noise levels at various blade-passage frequencies and harmonics. This paper will address the reduction of blade-rate noise. The hull boundary layer behind an appendage is characterized by a complex velocity field typically having velocity excesses at inner radii and velocity defects at the outer radii. This type of velocity field has a complex harmonic content distribution and its effect on blade-rate noise cannot be predicted without detailed examination of the wake and the radial distribution of propeller blade forces. The reduction of blade-rate noise and thus vehicle vibration provides the motivation for the application of skew in propeller design. Keywords: Turbulence injestion, Vortex shedding, Blade passage frequencies and harmonics, Blade rate.
Download or read book Noise and Performance of Propellers for Light Aircraft written by Massachusetts Institute of Technology. Gas Turbine & Plasma Dynamics Laboratory and published by . This book was released on 1980 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Noise Reduction on Weight and Cost of General Aviation Propellers written by Robert J. Klatte and published by . This book was released on 1979 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of a study are reported in which the influence of noise reduction on weight and cost of propellers used in General Aviation aircraft was evaluated. Aircraft performance was not to be degraded by installation of the reduced noise propellers. Only propeller modifications were permitted. Engine modifications, such as introduction of a gearbox to reduce noise by reduction of RPM, were not permitted in the study. Major factors in noise reduction found promising in the study were (1) optimization of performance by use of the best available airfoils, (2) use of thin airfoils and a narrow elliptical tip blade planform, and (3) increasing the number of blades consistent with maintaining aircraft performance. For the three aircraft studied (a single engine, a light twin and a heavy twin) the flyover noise reduction potential varied from 3 to 8 dBA with no weight or cost penalty. Greater reductions in noise resulted in increased weight and/or cost penalties. Also, in some cases, engine noise would have to be reduced to achieve greater reductions. The progress by General Aviation aircraft manufacturer's in reducing noise is indicated by the finding that the most recent aircraft design had the smallest noise reduction potential. (Author).
Download or read book Propeller Noise Caused by Blade Thickness written by Robert A. Arnoldi and published by . This book was released on 1956 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Optimization Method for the Reduction of Propeller Unsteady Forces written by Thomas S. Mauther and published by . This book was released on 1988 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Based on the work of Greenblatt (1978), an enhanced optimization technique for the reduction of propeller unsteady forces and the determination of skew distributions has been developed. The current method provides an efficient propeller design tool capable of determining a variety of cubic or quadratic skew distributions, subject to constraints, which minimize the unsteady forces produced by the various harmonic components of the input wake. The original skew optimization method was extended to include higher order harmonics, and the original force calculation method was replaced by an extended version of the method developed by Thompson (1976). Calculation of forces and skew distributions associated with a representative propeller show that acceptable reduction of unsteady forces can be obtained without having to place severe restrictions on the model constraints. The problem considered herein is the generation of propeller noise due to non-uniform inflow velocity fields. This has been still is an issue of research in the area of marine propellers, and it is felt that a recently developed method of calculating unsteady forces may also be applicable in the design and analysis of aircraft propellers. Angle-of-attack fluctuations result in unsteady blade loadings and the generation of propeller noise, and the noise sources are characterized by three types of unsteady force mechanisms: a) turbulence injection; b) vortex shedding; and c) blade-rate.
Download or read book Comparison of Sound Emission from Two blade Four blade and Seven blade Propellers written by Chester W. Hicks and published by . This book was released on 1947 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements of sound pressures for static conditions are presented for two-blade, four-blade, and seven-blade propellers in the tip Mach number range 0.3 to 0.9. The experimental results were found to check satisfactorily with those calculated by means of Gutin's formula for the whole Mach number range in the case of the two-blade propeller. Good agreement was obtained in the case of the seven-blade propeller for Mach numbers above 0.5, but large discrepancies were found to exist in the Mach number range below 0.5. Vortex noise is a large part of the total noise at low tip Mach numbers, especially for multiblade propellers, and therefore Gutin's formula is accurate for these conditions. Despite the discrepancies noted, an appreciable sound-pressure reduction may be realized by changing from a two-blade propeller to a seven-blade propeller for comparable operating conditions.
Download or read book Extensions to a Prediction Model for Propeller Noise Effects of Non uniform Inflow and Structural Blade Radiation written by M. H. A. Janssens and published by . This book was released on 2001 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Aeroacoustics of Low Mach Number Flows written by Stewart Glegg and published by Academic Press. This book was released on 2017-02-15 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aeroacoustics of Low Mach Number Flows: Fundamentals, Analysis, and Measurement provides a comprehensive treatment of sound radiation from subsonic flow over moving surfaces, which is the most widespread cause of flow noise in engineering systems. This includes fan noise, rotor noise, wind turbine noise, boundary layer noise, and aircraft noise. Beginning with fluid dynamics, the fundamental equations of aeroacoustics are derived and the key methods of solution are explained, focusing both on the necessary mathematics and physics. Fundamentals of turbulence and turbulent flows, experimental methods and numerous applications are also covered. The book is an ideal source of information on aeroacoustics for researchers and graduate students in engineering, physics, or applied math, as well as for engineers working in this field. Supplementary material for this book is provided by the authors on the website www.aeroacoustics.net. The website provides educational content designed to help students and researchers in understanding some of the principles and applications of aeroacoustics, and includes example problems, data, sample codes, course plans and errata. The website is continuously being reviewed and added to. Explains the key theoretical tools of aeroacoustics, from Lighthill’s analogy to the Ffowcs Williams and Hawkings equation Provides detailed coverage of sound from lifting surfaces, boundary layers, rotating blades, ducted fans and more Presents the fundamentals of sound measurement and aeroacoustic wind tunnel testing
Download or read book General Aviation Aircraft Design written by Snorri Gudmundsson and published by Butterworth-Heinemann. This book was released on 2013-09-03 with total page 1058 pages. Available in PDF, EPUB and Kindle. Book excerpt: Find the right answer the first time with this useful handbook of preliminary aircraft design. Written by an engineer with close to 20 years of design experience, General Aviation Aircraft Design: Applied Methods and Procedures provides the practicing engineer with a versatile handbook that serves as the first source for finding answers to realistic aircraft design questions. The book is structured in an "equation/derivation/solved example" format for easy access to content. Readers will find it a valuable guide to topics such as sizing of horizontal and vertical tails to minimize drag, sizing of lifting surfaces to ensure proper dynamic stability, numerical performance methods, and common faults and fixes in aircraft design. In most cases, numerical examples involve actual aircraft specs. Concepts are visually depicted by a number of useful black-and-white figures, photos, and graphs (with full-color images included in the eBook only). Broad and deep in coverage, it is intended for practicing engineers, aerospace engineering students, mathematically astute amateur aircraft designers, and anyone interested in aircraft design. - Organized by articles and structured in an "equation/derivation/solved example" format for easy access to the content you need - Numerical examples involve actual aircraft specs - Contains high-interest topics not found in other texts, including sizing of horizontal and vertical tails to minimize drag, sizing of lifting surfaces to ensure proper dynamic stability, numerical performance methods, and common faults and fixes in aircraft design - Provides a unique safety-oriented design checklist based on industry experience - Discusses advantages and disadvantages of using computational tools during the design process - Features detailed summaries of design options detailing the pros and cons of each aerodynamic solution - Includes three case studies showing applications to business jets, general aviation aircraft, and UAVs - Numerous high-quality graphics clearly illustrate the book's concepts (note: images are full-color in eBook only)
Download or read book Hovering Measurements for Twin rotor Configurations with and Without Overlap written by George E. Sweet and published by . This book was released on 1960 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Submarine Hydrodynamics written by Martin Renilson and published by Springer. This book was released on 2015-03-10 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book adopts a practical approach and presents recent research together with applications in real submarine design and operation. Topics covered include hydrostatics, manoeuvring, resistance and propulsion of submarines. The author briefly reviews basic concepts in ship hydrodynamics and goes on to show how they are applied to submarines, including a look at the use of physical model experiments. The issues associated with manoeuvring in both the horizontal and vertical planes are explained, and readers will discover suggested criteria for stability, along with rudder and hydroplane effectiveness. The book includes a section on appendage design which includes information on sail design, different arrangements of bow planes and alternative stern configurations. Other themes explored in this book include hydro-acoustic performance, the components of resistance and the effect of hull shape. Readers will value the author’s applied experience as well as the empirical expressions that are presented for use at the preliminary design stage. A wide range of state-of-the-art material is included, and there are over fifty references to recent publications in the field. Intended for advanced students and professionals working in the specialised field of submarine hydrodynamics, this book brings theoretical and practical knowledge together in one comprehensive work that is particularly valuable to the submarine hydrodynamicist.
