Beveled Nozzle Research Articles

Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

The importance of jet noise for prospective supersonic transport (SST) in takeoff and climb modes dictates the need to develop methods for reducing jet noise and their subsequent validation in large- and full-scale tests. This paper presents the results of Russia’s first ground acoustic tests of a rectangular nozzle with a noise suppression system, installed on a subsonic aircraft engine to demonstrate the technology. The authors studied a rectangular beveled nozzle with an ejector and screens—elements of the SST airframe. The test results were compared for three nozzle geometries: a round nozzle corresponding to measurements for the original engine without modifications, a rectangular nozzle without screens, and a rectangular nozzle with screens. It was found that when the rectangular nozzle without screens is used, there two opposite effects occur: noise amplification compared to the round nozzle for angles of observation close to the jet axis, and noise attenuation at angles of observation close to the fan rotation plane. Installing screens increases noise up to 5 dB in the low-frequency region below 150 Hz and reduces noise by 2 dB for frequencies higher than 250 Hz. Estimation of community noise in the EPNL metric showed that this rectangular nozzle with the noise suppression system has the effect of reducing community noise in comparison with the baseline round nozzle.

Vortex–shock and vortex–vortex interactions in the compressible starting jet from two beveled nozzle configurations

An experiment was conducted to investigate the flow structures in the compressible starting jet from two beveled nozzles (45 $$^{\circ }$$ and 30 $$^{\circ }$$ nozzle angles) of a shock tube using the schlieren technique. In the present study, the pressure ratios between the driver section and the driven section (PR) of 3.5, 7, and 10.5 corresponding to the shock wave Mach numbers ( $$M_\mathrm{s}$$ ) of 1.28, 1.48, and 1.59 were applied to produce three types of compressible vortex rings (CVRs). Owing to the beveled nozzle, the shock wave diffracts twice to produce two coaxial CVRs. For PR = 3.5 with 45 $$^{\circ }$$ beveled nozzle, two shock-free CVRs are formed and merged into one primary CVR, while the two CVRs are separated from each other for the 30 $$^{\circ }$$ beveled nozzle. The main reason is that the strength of the secondary CVR generated from the 30 $$^{\circ }$$ beveled nozzle is much lower than that of the leading CVR. As for PR =7 and 10.5, the embedded shock and counter-rotating vortex rings (CRVRs) appear and constraint the formation of the secondary CVR. As a result, the two CVRs are merged into a primary CVR at a very early stage. In addition, for the two different beveled nozzles, the embedded shock–CVR, CRVR–CVR, and shock cell-trailing vortices interactions are observed and exhibited some differences. Moreover, by identifying the position of the primary CVR, it is found that the propagation velocity of the primary CVR generated from the beveled nozzles is significantly slower than that from a straight nozzle.

The influence of nozzle geometry on the gas-dynamic structure of the supersonic nonisobaric jet

The paper presents the investigation results of the flow structure of cold supersonic jets flowing out of model nozzles with a Mach number on the exit Ma = 3.5: an axisymmetric nozzle, a nozzle with a rectangular critical section, a beveled nozzle with a rectangular critical section. Flow schlieren images and transverse measured total pressure profiles in the flow are presented. The influence of the critical section shape and the beveled exit section on the shock-wave structure of the flow is described.

Experimental and Numerical Study of Hydrodynamic Characteristics of Gullies for Buildings

The miniaturization of a gully for building drainage system is attempted by installing a streamlined bump in the discharge pipe to maintain the minimum water trap height of 50 mm. The hydrodynamic performances of the air–water flows with or without glass balls through the two types of four-entry gullies with beveled or vertical nozzle flows are experimentally and numerically studied. The images of air–water–solid flow, maximum flow rates, self-purification properties and sustainable water traps subject to static and dynamic loadings are experimentally detected. The predictions of Computational Fluid Dynamics (CFD) unravel the characteristic flow structures to assist the interpretation of experimental results. In this respect, the observed entrained air bubbles and clustered glass balls in each gully correspond favorably to the regions with negative static pressures and weak flow momentums as disclosed by the CFD predictions. The measured ratios between discharged and supplied glass balls are consistently higher for the gully with beveled nozzle flows. The less efficient transportation of glass balls out of the drum for the gully with downward nozzle flow is attributed to the larger pressure gradients with considerable air entrainments. The relaxations of the form and friction drags over the nozzle-tip region and the reductions of air entrainments are essential for upgrading the maximum flow rate and the self-purification performance of a miniaturized gully.

Experimental investigation on the near flow field of dual stream nozzles

An experimental investigation was carried out to investigate the effect of beveling of primary nozzle exit in the near field of a dual stream nozzle flow. Two exit geometry configurations of primary stream nozzle viz., (a) circular (b) bevel along with one exit geometry of the secondary stream-circular, were studied. Experiments were carried out at both subsonic and supersonic primary nozzle operating conditions Mp=0.96 and 1.2. The secondary nozzle exit Mach number was maintained at 0.65 and 0.85 respectively to maintain the velocity ratio of 0.7 between the primary and secondary jet. The by-pass ratio for this investigation is maintained at 2.0. Flow visualization using retro-reflective shadowgraph technique was used for the qualitative visualization of the near flow field at the Mach number of 1.2. The mean and turbulent quantities in near flow field were obtained using particle image Velocimetry (2D-PIV). The flow visualization and PIV investigations show significant change in mean and turbulent quantities brought about in the near field due to the beveling of the primary nozzle. PIV results show increase in the potential core length and reduction in turbulence levels in the potential core by the secondary flow regardless of the jet exit geometry. A differential trend is seen in the shear layer growth and the turbulence characteristics between the shorter and longer lips sides of the beveled nozzle. In the dual stream configurations, bevel nozzle shows lower Reynolds stress values than the circular one except in the shorter lip side at the larger downstream locations.

Acoustics measurements of military-style supersonic beveled nozzle jets with interior corrugations

Increasingly powerful and noisy military aircraft have generated the need for research leading to the development of supersonic jet noise reduction devices. The hot, high speed supersonic jets exhausting from military aircraft during takeoff present a most challenging problem. The present study extends prior research on two methods of noise reduction. The first is the internal nozzle corrugations pioneered by Seiner et al. and the second is the beveled exit plane explored most recently by Viswanathan. A novel research idea of creating fluidic corrugations similar to the nozzle corrugations has been initiated by Penn State. To further the understanding and analysis of the fluidic corrugations, the present study focuses on the flow field and acoustic field of nozzles with two, three, and six conventional, hardwalled corrugations. The effect of the combination of the internal corrugations with a beveled nozzle is explored. The results show that significant noise reductions of over 3 dB of the mixing noise and the broadband shock-associated noise can be achieved. The combination of the beveled nozzle and the internal nozzle corrugations showed that there is less azimuthal dependence of the acoustic field than for the purely beveled nozzle. The combination nozzle was shown to reduce the noise over a wider range of polar angles and operating conditions than either the purely beveled nozzle or the purely corrugated nozzle.

Comparative studies on supersonic free jets from nozzles of complex geometry

Experimental and numerical studies are conducted to compare free jets from different supersonic nozzles for mixing enhancement. A conical nozzle of Mach 1.80 is the reference. Three complex nozzles are a beveled nozzle, a nozzle with six chevrons and a six lobed ESTS nozzle.All nozzles have the same throat diameter and designed average exit Mach number. The studies are conducted at NPR = 6, using acetone PLIF, centerline pitot pressure measurements, and 3D RANS simulations. A novel method of decomposing PLIF images based on intensity histogram and then recomposing after applying selective gains to emphasize the growth of shear layers is discussed. PLIF images are processed to extract the growth rate of jet width which indicates the rate of mixing. The ESTS lobed nozzle shows the highest enhancement of mixing (430%) followed by chevron (222%) and the beveled nozzle with a moderate (138%). The numerical simulations are validated and agree well with experimental results. ESTS lobed nozzle is found to produce widespread streamwise vortices compared to clustered vortices of the chevron nozzle. The mechanism of streamwise vorticity production from ESTS nozzle is clarified for the first time in this study.

An Experimental and CFD Investigation of a Supersonic Nonisobaric Jet Exhausting From a Beveled Nozzle

The aim of the investigation is to understand the shock-wave structure of the supersonic jet exhausting from a beveled nozzle. Results of investigation are presented as cross section Pitotpressure fields. This data can be used for verification of CFD results. The experiment was complemented by numerical simulation with using of the program packet ANSYS Fluent. The satisfactory qualitative agreement was obtained

Adaptation of the Beveled Nozzle for High-Speed Jet Noise Reduction

The noise of high-speed jets, generated by nozzle exhaust systems that resemble typical jet engine installations on fighter aircraft, has been investigated with the main objective of developing noise reduction designs. To this end, the aeroacoustic characteristics of beveled nozzles have been examined in model scale tests and their performance relative to a conventional round nozzle system has been established. Two different physical models with appropriate area ratios to simulate the engine operating conditions at different power settings were tested; these correspond to 96% N1 (Military or MIL power) and 91% N1 (cutback power). Aeroacoustic measurements and analyses have been carried out for nozzles at bevel angles of 20o, 24o, 28o and 35o for MIL power, and 24o and 32o for cutback power. For the same plenum conditions, the mass flow rates for the beveled nozzles are identical to those of the baseline round nozzle, for a wide range of NPR. The thrust coefficients are higher for the beveled nozzles for both the nozzle geometries at typical MIL power and cutback power, respectively. The increase in the thrust coefficient ranges from ~0.75% for the bevel35 to ~2% for bevel28, in spite of the slight deflection of the jet plume. The reasons for this phenomenon are examined. The beveled nozzles produce at least the same or greater absolute thrust as the baseline nozzle. The beveled nozzles specifically reduce the noise in the peak polar radiation angles; the maximum noise benefit is observed in the azimuthal direction of the longer lip. The magnitude of noise reduction increases with increasing bevel angle, with the largest reduction for bevel35. An examination of the dBA metric, which is used in noise exposure studies, indicates that there is a noise benefit of ~3 dBA to ~4 dBA in the peak radiation sector. The noise benefit in the azimuthal direction of the shorter lip is only slightly lower than that in the direction of the longer lip. I. Introduction he noise of high-speed jets, as from the engines that power fighter aircraft, is a major concern for both military personnel and civilians living close to military bases. Military jets are powered by turbojets or very low bypassratio turbofan engines (BPR ≤ 0.3). The attendant high jet velocities produce extremely high levels of jet noise. This problem is severe for operations on aircraft carrier decks because military personnel are stationed very close to the aircraft during the launch and the landing of carrier-based fighter aircraft. Pilots perform training missions, called Field Carrier Landing Practice, at military bases that mimic the actual flights at the appropriate engine power settings, thereby creating a huge noise problem for the surrounding communities. The magnitude of the problem is first highlighted with a comparison of the noise footprints from the F/A-18 A/B and the Boeing 737-800 aircraft. The noise foot print is calculated as follows: first, A-weighted spectra are calculated from the measured spectra over a wide range of radiation angles. The A-weighting adjusts the full-scale spectrum measured by the microphone to account for the response of the human ear, with the low frequency levels decreased by several decibels, and the high-frequency portion of the spectrum relatively unmodified. The energy levels in the resulting spectrum at the different frequencies are logarithmically summed to produce one dBA number at each angle. The maximum dBA

Investigation of Noise Source Mechanisms in Subsonic Jets

The precise nature of the origin of jet noise remains in question to this day. Apart from the scientific importance of gaining a better understanding of the noise sources, there is the practical consideration of our ability to alter/ manipulate the sources so as to achieve noise reduction. In this study, the sources of jet noise have been investigated with 1) the analyses of far-field spectra, and 2) the measurements of the far-field correlations, both in the polar and azimuthal directions. Two geometries were used: a round nozzle and a beveled nozzle. The acoustic characteristics of these nozzles exhibit interesting trends at different jet velocities (Vj/a), thereby permitting a better understanding of the nature of the noise sources. The far-field spectra from unheated round jets at extremely low Mach numbers conform to the large-scale similarity shape at angles close to the jet axis; there is a gradual progression from the fine-scale similarity shape to the large-scale similarity shape for all jet velocities. This seems to be a fundamental characteristic of jet noise and is a new finding. The far-field correlations indicate that there is very little correlation at the lower polar angles; in the peak aft radiation sector, high correlations prevail. It is established with both the round and beveled nozzles that low correlations are associated with fine-scale-similarity-shaped spectra and high correlations with large-scale-similarity-shaped spectra. Experimental evidence for the importance of the noise from large coherent structures even at low velocities is offered. The data indicate the existence of two independent sources in both high-speed and low-speed jets, with the coherent large structures radiating to the aft angles and the random turbulence radiating to the lower angles. It is shown that the noise reduction of the beveled nozzle is due to the alteration of the noise from the coherent structures. The beveled nozzle thus provides indirect evidence for the importance of large coherent structures.

Noise of Dual-Stream Beveled Nozzles at Supercritical Pressure Ratios

The nozzles of a dual-stream turbofan engine are operated invariably at supercritical pressure ratios at cruise, thereby producing shocks in the jet plume. Consequently, broadband shock-associated noise is generated in addition to turbulent mixing noise. The jet exhaust noise impinges on the fuselage and is then transmitted into the interior of the aircraft cabin. In a companion paper, the beveled nozzle has been shown to provide a community noise benefit during takeoff. (Viswanathan, K., Elegant Concept for Reduction of Jet Noise from Turbofan Engines, Journal of Aircraft, Vol. 43, No. 3, 2006, pp. 616-626.) Here, the aeroacoustic characteristics of two beveled nozzles, with bevel angles of 24 deg (bevel24) and 45 deg (bevel45), operated at supercritical pressure ratios, are presented under static conditions as well as in the presence of a Mach 0.32 flight stream. The intended application is for the control of aft-cabin noise. The velocity of the primary jet plays a strong role in the reduction of noise at the aft polar angles, with a substantial benefit at higher jet velocities. The magnitude of reduction in overall levels for bevel45 at the aft angles ranges from ∼5 to ∼12 dB under static conditions, depending on the Mach number of the secondary stream. In the presence of a flight stream, the jet conditions, as well as the bevel angle, control the flight effects at different azimuthal angles. It is demonstrated that at typical cruise power settings, the current concept with bevel24 yields a reduction of ∼4 dB in overall levels; the reduction occurs over a wide range of lower frequencies without any increase at the higher frequencies. Given this reduction in impingement levels on the rear fuselage, this design could yield a cabin noise benefit in addition to the benefit for community noise at takeoff conditions.

Elegant Concept for Reduction of Jet Noise from Turbofan Engines

Jet noise is a major component of total aircraft noise at takeoff, even for modern aircraft powered by high-bypass-ratio (BPR) turbofan engines with BPR of around five. The reduction of jet noise at fixed BPR has proven to be a formidable challenge, and no practical design that produces substantial aeroacoustic benefit has evolved despite significant effort. A simple concept of a beveled nozzle is adapted for realistic engine geometries. The strategy for noise reduction in the peak sector of noise radiation is based on our understanding of the characteristics of the noise sources in a dual-stream exhaust system. Specifically, the noise generation mechanisms of the inner shear layer are modified by beveling the primary nozzle to achieve noise reduction. Detailed aeroacoustic measurements are carried out statically and in the presence of a flight stream to assess the noise benefit of the modified exhaust system, relative to a conventional arrangement, at realistic engine cycle conditions. Two beveled nozzles of bevel angles 24 (bevel24) and 45 deg have been evaluated. The bevel24 nozzle has a low performance penalty (∼0.2%) at cruise power and produces substantial reduction in noise levels in the aft quadrant. The reduction in overall sound pressure levels is ∼5 to ∼7 dB near the spectral peak in the angular sector >110 deg. There is a slight increase (∼1 dB) in the overall sound pressure levels at the lower polar angles. The magnitude of noise reduction is strongly dependent on the velocity of the inner stream. The reduction in levels occurs over a wide frequency range; there is no increase at the higher frequencies, which is a typical trend for other noise reduction concepts. The effects of forward flight on the measured spectra are different at different azimuthal angles; further, the flight effects in the azimuthal plane are a function of the bevel angle. A total noise reduction of ∼4 dB effective perceived noise level is demonstrated at takeoff (sideline and overhead) at realistic flight Mach numbers with the bevel24 nozzle.

Nozzle Shaping for Reduction of Jet Noise from Single Jets

There is a wide body of evidence that suggests that the turbulent mixing noise from high-speed jets consists of two components. These two components are generated by sources/mechanisms associated with the fine-scale turbulence and the large-scale structures of the jet plume. The noise generated by the large-scale structures radiates predominantly to the aft quadrant and typically peaks at angles close to the jet axis. The noise from the fine-scale turbulence is dominant in the forward quadrant and at near-normal angles to the jet axis. The initial objective of this study is to find a means to alter this basic radiation process in a high-speed jet. The ultimate goal of this study, however, is the achievement of noise reduction by accomplishing the preceding objective. A simple concept, ab eveled nozzle, is proposed, and detailed aeroacoustic measurements are performed on two nozzles of different bevel angles. Noise measurements, over a wide range of polar angles, are made at several azimuthal angles to map the azimuthal variations. The performances of the beveled nozzles are assessed against a reference round nozzle. The beveled nozzles introduce significant azimuthal variations in the spectra, resulting in major differences in the polar directivities of the overall sound pressure levels at different azimuthal angles; these differences become pronounced when the jet velocity is increased. It is demonstrated that significant noise reduction is achieved in the azimuthal directions below the longer lip of the beveled nozzle, principally in the polar angular range of ∼110 to ∼140 deg. Furthermore, this reduction is observed at all frequencies, with a low performance penalty of ∼1%. The magnitude of the noise reduction is a strong function of the jet velocity, with progressively higher reductions as the jet velocity is increased. With proper orientation of the nozzle, the noise footprint on the ground can be reduced. It is shown that the noise reduction is caused by the modification of the noise generated by the large-scale structures in the jet plume. Thus, noise reduction is achieved through the manipulation of the generation mechanisms. HERE is a wide body of evidence that suggests that the turbulent mixing noise from high-speed jets consists of two components. These two components are generated by sources/mechanisms associated with the fine-scale turbulence and the large-scale structures of the jet plume. The noise generated by the large-scale structures radiates predominantly to the aft quadrant and typically peaks at angles close to the jet axis. The noise from the fine-scale turbulence is dominant in the forward quadrant and at near-normal angles to the jet axis. As the jet velocity is increased, there is a broadening of the angular sector in which peak radiation occurs, with more noise being radiated to lower polar angles. (All polar angles are measured from the jet inlet axis, with the jet exhaust axis corresponding to

Side force augmentation at high angle of attack from pneumatic vortex control

An experiment has been undertaken to measure side and lift forces with various nozzle blowing locations on an elliptic fore body. In this study a jet of small momentum excites a corrective instability to produce an amplified side force at high angle of attack for a fighter forebody. This study has identified an optimized nozzle position around the circumference of the forebody and axial location using a slotted nozzle at various pressure ratio values. A forward sweep of the nozzle provided for the greatest augmentation of side force at angles of attack below 55 deg. A beveled nozzle has shown active control of side force beyond 55-deg angle of attack and has merit in extending the angle of attack range. The mass flow requirements to produce a side force are sensitive to the angle of the jet relative to the forebody axis. The required mass flow is compatible with available engine bleed air that could be dedicated to pneumatic control. Data for different forebody strake configurations shows a degradation in side force magnitude with pneumatic blowing.