COMPLETE SPECIFICATION

Inventors: Sathyaprabha R Vigneshwaran S Manishaa R AjithS Sivabalan M V.R.Sanal Kumar
Date: 05.01.2016

Reference Cited:

US Patent No: US 10/988,286 US Patent No: US 11/536,790

Title of Invention:

Environmental Friendly Chevron Nozzle for Lower Stage Rockets Field of Invention:

This invention relates to the field of Aerospace Science and Technology.

State of the Art and Background Technology:

The noise regulations around the major airports and rocket launching stations due to the environmental concern have made jet noise a crucial problem in the present day aero-acoustics research. Since the frequency of the orbital and the sub-orbital rocket launching are increasing world-wide, the heed of negating the noise pollution is highly inevitable for humankind. The three main acoustic sources in jet nozzles are aerodynamics noise, noise from craft systems and engine and mechanical noise. The literature review reveals that the majority of engine noise is due to the jet noise coming out from the exhaust nozzle. Literature review further reveals that the nozzle with chevrons was widely used in aircraft engines and ejector systems for jet noise reduction but it seldom used in rockets. As a rocket is launched into space, the Mach number of the rocket goes from zero to almost 30. The previous studies reveal that the potential of chevron nozzles for aircraft engines noise reduction is promising owing to the fact that the jet noise continues to be the dominant noise component, especially during take-off. Acoustic studies reveal that addition of chevrons to the nozzle reduces the sound pressure level reasonably well with the acceptable reduction in performance. Although many studies were carried out by the earlier investigators on jet acoustics the understanding of the fundamental mechanisms responsible for the acoustic benefit and the influence of various geometric parameters of chevrons for noise suppression are not well connected. Parameters such as, the number of chevron lobes, the lobe length and the level of penetration of the chevrons into the flow have been investigated over a variety of flow conditions. It is well known that the high velocity jet leaving back of the engine has inherent shear layer instability and rolls up into ring vortices. This later breaks down into turbulence sources of jet noise at the exit of nozzle. Note that each of the chevrons is triangular in configuration, with a base, apex, side trailing edges converging. there between, and radially opposite first and second surfaces bounded thereby. The trailing edges of adjacent chevrons are spaced laterally apart to define respective diverging slots disposed in flow communication with the duct. The chevrons have a concave contour axially between the bases and apexes which promotes jet mixing through the slots. Shaped edges of the nozzle play an important part in smooth mixing of the flow which significantly reduces turbulence (pressure fluctuation), a cause of noise creation. The proposed chevron design is inherently different than the existing chevron for aircraft noise reduction.

The open literature reveals that the Aero Acoustic Propulsion Lab (AAPL) at NASA Glenn Research Center [2000] carried out a series of parametric chevron tests on the Small Hot Jet Acoustic Rig (SHJAR) at an acoustic Mach number of 0.9 aimed for establishing the relationships between chevron geometric parameters, flow characteristics, and far-field noise. The comprehensive experimental studies of Saiyed et al. [2000] at NASA reveal that the chevron modification to the round nozzle can bring as much as 3 dB reduction in peak noise during take¬off with less than 0.5% thrust loss during cruise. For high frequencies and large angles to the jet, the use of chevrons may also lead to about to 2 dB noise increase.. This naturally leads to the chevron design optimization problem in which eddy resolving numerical simulations and acoustic modeling techniques for jet noise prediction play an important potential role. Note that all these papers were published for aircraft and none discussed about the promising design of chevron for rockets and missiles. In this patent an attempt has been made for the design and geometry optimization of chevron nozzles for rockets and missiles without scuttling the mission demanding thrust-time requirements.

Object of the Invention

Admittedly, the frequency of the orbital and the sub-orbital rocket launching are increasing world-wide and the need of negating the jet noise pollution is highly inevitable for humankind. The object of this invention is to design and qualify a unique chevron nozzle for jet noise reduction without affecting the overall performance of the rocket.

Disclosure of the Invention:

The Chevron technology has provided a modest relief for jet noise reduction in rockets and missiles. We have observed that the shape optimizations of chevron nozzle have a potential for the reduction of turbulent mixing noise, which is believed to be the dominant component of jet noise for supersonic nozzles. We have inferred that the suitable selection of the chevron shape based on the exit Mach number range and the. proper number of round edge chevrons with aerodynamically efficient tip contours will enable an appreciable reduction of the jet noise at different frequencies without much compromising on the overall nozzle performance and the payload capability of launch vehicles. This is due to the fact that chevron crown can be facilitated to any rocket nozzle without increasing the nozzle weight and without much compromising on its liftoff thrust. We concluded that the existing rocket nozzle can be converted into an environmental friendly chevron nozzle with better liftoff performance without changing the total weight of the nozzle and the effective nozzle area ratio. This paper is a pointer towards for the geometry optimization of environmental friendly chevron nozzles for the future launch vehicle applications without sacrificing the mission demanding the thrust-time requirements.

Scope of this Invention

This patent is a pointer towards for the geometry optimization of environmental friendly chevron nozzles for the future aerospace vehicle applications (both rockets and missiles) without sacrificing the mission demanding the thrust-time requirements.

Performance Details of the Chevron Nozzle In this patent different case of chevron nozzles with round tips contours are selected for the jet acoustic characterization and its geometric optimization of a traditional rocket nozzle having the same area ratio for establishing the merits of the chevron crown for reducing the acoustic power level of lower stage rockets motors without affecting the overall performance of the rocket. Figure l(a-c) shows different rocket nozzles. Figure 1(a) (Base model) is the conventional CD nozzle for rockets and missiles and Fig. 1(b) is a chevron nozzle with reduction in weight (Case-1). Figure 1(c) is the proposed chevron nozzle design (Case-2) without much altering the total weight of the nozzle. Figures 2(a-c) & 3(a-b) are showing the physical model of the nozzles and its side views. It is evident from the parametric analytical studies that a slight difference in the chevron geometry makes a large difference in the noise benefit without any thrust penalty. Analyses reveal that suitable penetration by the chevrons is necessary to achieve good noise benefit. Chevron penetration was identified as the primary factor controlling the trade-off between low-frequency reduction and high-frequency increases. We observed that for a given number of chevrons with a particular geometry, there should be an optimum penetration. We also observed that the prudent selection of optimum number of chevron is important for jet noise reduction. Thus, for a given number of chevrons with aparticular geometry, there should be an optimum penetration. In this patent we have prudently generated number of chevron as 9 and fixed with conventional CD nozzle of a rocket without adding any weight and without altering the effective nozzle area ratio.

Evidently, one way of understanding the chevron nozzle flow is in terms of vorticity distributions. With the baseline nozzles, the vorticity in the shear layer is primarily composed of the azimuthal component. Such vorticity concentrates into the discrete ring-like (or helical) coherent structures. These structures go through contortions and interactions while propagating downstream. Their dynamics are unsteady and vigorous giving rise to high turbulence intensities. Note that the only source of vorticity in the flow is the efflux boundary layer of the nozzle. All these lead to say that the chevrons simply redistribute part of it into the streamwise component at the expense of the azimuthal component. Thus, the chevrons having tips with aerodynamically efficient contortions arrest the vigorous activity of the azimuthal coherent structures to some extent via introduction of the streamwise vortices. The result often is a reduction in the turbulence intensities that correlates with the noise reduction. Overall this patent reveals that chevron technology has provided a reasonable relief for jet noise reduction without much affecting the takeoff thrust of launch vehicles. We have concluded that, while comparing with the conventional CD rocket nozzle, chevron with nine lobes having round tips is better for reducing the acoustic power level on the order of 6.61% (see Fig.4) and increasing the momentum thrust on the order of 0.4% (see Fig.5). Figures 6 & 7 are corroborating our invention.

Henceforth we put forward the following independent 10 claims.

Claim 1: We claim that although the nozzle with chevrons was widely used in aircraft engines and ejector systems for jet noise reduction but it is not designed for rockets and missiles.

Claim 2: We claim that, while comparing with the existing rocket nozzles our unique design of chevron nozzle with nine lobes is better for reducing the acoustic power level on the order of 6.61 %.

Claim 3: We claim that our unique design of chevron nozzle with nine lobes is better for reducing the acoustic power level and increasing the momentum thrust on the order of 0.4 %

Claim 4: We claim that our unique design of chevron nozzle with nine lobes is showing better performance for rockets and missiles than a case with eight lobes, which was designed for aircraft.

Claim 5: We claim that our unique design of chevron nozzle with nine lobes will not contribute additional weight and hence it will give better payload capability and thrust augmentation.

Claim 6: We claim that that the round edge chevrons with aerodyhamically efficient tip contours will enable an appreciable reduction of the jet noise at different frequencies without much compromising on the overall nozzle performance of the launch vehicles.

Claim 7: We claim that the chevron crown can be facilitated to any existing rocket nozzle without much increase in the nozzle weight and without much compromising on its liftoff thrust.

Claim 8: We claim that the existing rocket nozzle can be converted into an environmental friendly chevron nozzle with suitable number of chevron with better liftoff performance without changing the total weight of the nozzle and the effective nozzle area ratio.

Claim 9: We claim that the proposed nine lobes round chevron with round tips is the first generation nozzle for rockets and missiles for jet noise reduction.

Claim 10: We claim that the proposed nine lobes chevron is unique and got various industrial applications.