New Design of the Reversible Jet Fan

This paper presents two designs of the axial reversible jet fan, with the special focus on the impeller. The intention was to develop a reversible axial jet fan which operates in the same way in both rotating directions while generating thrust as high as possible. The jet fan model with the outer diameter 499.2 +/- 0.1 mm and ten adjustable blades is the same, while it is in-built in two different casings. The first construction is a cylindrical casing, while the second one is profiled as a nozzle. Thrust, volume flow rate, consumed power and ambient conditions were measured after the international standard ISO 13350. Results for both constructions are presented for three impeller blade angles: 28 degrees, 31 degrees and 35 degrees, and rotation speed in the interval n = 400 to 2600 rpm. The smallest differences in thrust, depending on the fan rotation direction, as well as the highest thrust are achieved for the first design with the cylindrical casing and blade angle at the outer diameter of 35 degrees. Therefore, it was shown that fan casing significantly influences jet fan characteristics. In addition, the maximum thrust value and its independence of the flow direction is experimentally obtained for the angle of 39 degrees in the cylindrical casing

New Design of the Reversible Jet Fan

This paper presents two designs of the axial reversible jet fan, with the special focus on the impeller. The intention was to develop a reversible axial jet fan which operates in the same way in both rotating directions while generating thrust as high as possible. The jet fan model with the outer diameter 499.2 +/- 0.1 mm and ten adjustable blades is the same, while it is in-built in two different casings. The first construction is a cylindrical casing, while the second one is profiled as a nozzle. Thrust, volume flow rate, consumed power and ambient conditions were measured after the international standard ISO 13350. Results for both constructions are presented for three impeller blade angles: 28 degrees, 31 degrees and 35 degrees, and rotation speed in the interval n = 400 to 2600 rpm. The smallest differences in thrust, depending on the fan rotation direction, as well as the highest thrust are achieved for the first design with the cylindrical casing and blade angle at the outer diameter of 35 degrees. Therefore, it was shown that fan casing significantly influences jet fan characteristics. In addition, the maximum thrust value and its independence of the flow direction is experimentally obtained for the angle of 39 degrees in the cylindrical casing

Investigation of the Muffling Problem for Airplane Engines

The experimentation presented in this report falls in two divisions: first, the determination of the relation between back pressure in the exhaust line and consequent power loss, for various combinations of speed and throttle positions of the engine; second, the construction and trial of muffler designs covering both type and size. Report deals with experiments in the development of a muffler designed on the principle which will give the maximum muffling effect with a minimum loss of power. The main body of the work has been done on a Curtiss OX eight-cylinder airplane engine, 4 by 5 inches, rated 70 horsepower at 1,200 revolutions per minute. For estimation of the muffling ability and suppression of "bark" of individual exhausts, the "Ingeco" stationary, single cylinder, 5 1/2 by 10 inch, throttling governed gasoline engine, and occasionally other engines were used

Shock-cell noise investigation on a subsonic/supersonic coaxial jet

The work is aimed at the experimental investigation of shock-cell noise on a coaxial jet with subsonic primary stream and supersonic secondary stream. This kind of noise is nowadays an important component of the total noise emitted by aeronautic engines, particularly affecting cabin noise in cruise conditions. In this thesis, the design and commissioning of a new supersonic coaxial jet rig, at the von Karman Institute for Fluid Dynamics (BE), are discussed, with a specific focus on the design choices that have been made to obtain good flow quality, low background noise and the possibility to perform a variety of flow and acoustic measurements. The maximum achievable Mach number at the outlet of the primary (central) and secondary (annular) nozzles is equal to 2.2, with a baseline operating point being M_p=0.89, M_s=1.21. To commission the facility, several test campaigns on a supersonic single stream jet were conducted using PIV in synchronous with microphones mounted on a polar antenna. Multiple screech harmonics and subharmonics tones have been documented, showing a directivity pattern similarly to the supersonic broadband noise (BBSAN). Turbulence integral length scales have been computed using correlation functions. The average of Reynolds shear stress fields shows the presence of lobes in the jet near field which are the trace of a standing wave caused by the screech. Following the commissioning, the coaxial jet has been investigated. Multiple combinations of pressure conditions for the primary and secondary flows have been tested. Acoustic measurements have been performed in synchronous with the PIV, which has been applied for the first time in the literature on a supersonic coaxial flow. The presence of both screech and broadband noise was recorded in the majority of the tests, and a directivity pattern was recognized for the latter. For a certain pressure conditions, the screech tone naturally disappeared. Experimental evidences suggest this may be related to a complex shock interaction occurring at the end of the primary nozzle. A simple method to infer the screeching dynamics from the spatial correlation functions was proposed. The correlation suggests the presence of a pulsation (or breathing) motion of the internal jet, which is cause/effect of the screech. A second screech mode was also retrieved from acoustic data, for which, the correlation functions suggest the presence of a sinusoidal motion of the internal jet

Numerical Simulation of Shock Wave Propagation in Ducts with Grooves

The pressure attenuation of moving shocks when they propagate in ducts, is of great importance in a wide variety of applications, such as health, safety, and transportation. The objective of this research is to simulate the propagation of shock waves in ducts with roughness. The roughness is added in the form of grooves as in an existing experiment. Different shapes are considered in order to better understand the physics behind the evolution of the complex shock patterns resulting from diffraction, reflection and refraction of the primary moving shock. The contribution of grooves and duct shape on these phenomena and pressure attenuation is investigated. The numerical method is validated through several test cases, and the results are compared against the theory and the experimental measurements. Good agreement between high resolution computations and the experiment is obtained for the shock speeds and complex wave patterns created by the grooves. Time histories of pressure at various locations are also compared. It is found that accurate pressure history agreement requires a close representation of the full experimental setup to fully capture boundary layer development, and pressure losses associated with unsteady moving shocks in long ducts. Different groove geometries have been tested in the numerical computation in order to identify the shape that will diminish shock strength, hence pressure extrema more effectively. Analysis and animations of the computed results are employed to reveal salient features of the unsteady flowfield

Handbook for industrial noise control

The basic principles of sound, measuring techniques, and instrumentation associated with general purpose noise control are discussed. Means for identifying and characterizing a noise problem so that subsequent work may provide the most efficient and cost effective solution are outlined. A methodology for choosing appropriate noise control materials and the proper implementation of control procedures is detailed. The most significant NASA sponsored contributions to the state of the art development of optimum noise control technologies are described including cases in which aeroacoustics and related research have shed some light on ways of reducing noise generation at its source

Acoustic investigation of perforated liners in gas turbine combustors

Modern combustion systems in industrial applications, from the gas turbine to aero or rocket engines, have become more critical during the last few years due to an exponential increase in commercial air traffic, resulting in an elevated level of atmospheric pollution in the form of exhaust smoke. To develop an efficient combustion system under variable load conditions, bias flow has been introduced progressively in the flame tube to decrease the temperature of the combustor liner in a consistent manner. Additionally, it is introduced as a passive damping device to increase the acoustic energy absorption from the system.This thesis amalgamates gas turbine combustor liner acoustic and static pressure measurements, along with their predictions. The primary objective of this investigation is to identify the passive damper maximum acoustic energy absorption properties. It will also collect information for designers to develop a cylindrical combustor liner geometry, along with flow factor, thermodynamic property and acoustic factors. A series of experiments was conducted, and the outcome of the investigation was compared with prior research, simulated data, and predictions to validate how this examination can be fundamental in advancing modern combustion systems.The results suggest that non-zero bias flow can greatly improve energy absorption and shift the peak frequency; the system operates as a Helmholtz resonator. Static pressure measurements suggest that as the mass flow rate changes, so too does pressure ratio, which creates a nonlinear absorption property of the combustor. The liner with the lowest porosity creates the pressure curve for double layer combustors. This could prove useful in assisting architects to utilize the combustor as a damper, metering liner or, indeed, a combination of both. A semi-empirical hybrid model is developed based on experimental data

Конструктивні підходи щодо зменшення рівня шуму літака

Робота публікується згідно наказу Ректора НАУ від 27.05.2021 р. №311/од "Про розміщення кваліфікаційних робіт здобувачів вищої освіти в репозиторії університету". Керівник роботи: доцент, к.т.н. Юцкевич Святослав СергійовичThis master thesis is dedicated to research of the noise control and reduction method in the aircraft design process and improving low frequency sound absorption performance of the micro-perforated panel honeycomb sandwich structure within space-coiling. The design methodology is based on the principles of aeroacoustics, the theory of micro-perforated panel, computer-aided design, and finite element analysis. Practical value of the work is improving the aircraft noise reduction performance on the base of the micro-perforated panel honeycomb sandwich structure application. The materials of the master's diploma can be used in the aviation industry and in the educational process related to aircraft noise reduction.Ця магістерська робота присвячена дослідженню методу контролю та зменшення шуму на етапі проектування літального апарату та покращенню характеристик низькочастотного звукопоглинання мікроперфорованої панелі стільникової сендвіч-конструкції в зовнішнього контуру. Методологія розробки базується на принципах аероакустики, теорії мікроперфорованої панелі, автоматизованого проектування та скінченно-елементного аналізу. Практичною цінністю роботи є підвищення ефективності шумозаглушення літака на основі застосування мікроперфорованої панелі сотової сендвіч-конструкції. Матеріали диплома магістра можуть бути використані в авіаційній промисловості та в навчальному процесі, пов’язаному зі зниженням шуму літаків