Description: Field of Invention
The present invention pertains to reduce the noise level with minimum thrust loss in the Ramjet powered tip jet helicopters.
Background of the invention
Aircraft noise is a great issue nowadays which creates an impact on environment, finance, and technology. There are two types of sources of noise from the aircraft engine and they are from aircraft compressor or fan and from the flow of jet. And the interaction of the rotor viscous wakes with guide vanes at the fan exit or the stator is also the main reason for the production of noise. Even the noise emitted from the mechanical linkages inside the engine system. The jet noise arises because of the imperfect turbulent mixing of jet and imperfect jet expansion. Till now turbulent mixing in the jet is a challenging one and this is under research.
The noise generated by supersonic, high temperature jets that exhaust from military aircraft is a continuing major problem. Practical active techniques to reduce the noise produced by low bypass ratio turbofan engine jets in a realistic full - scale environment is difficult. This project explores the use of hard-wall corrugations in a round convergent nozzle as a preliminary result to determine the possible effectiveness of noise reduction.
For instance US2987883 discloses the operation of aerodynamic supplemental flute nozzle. In accordance with this invention, a moderately corrugated basic nozzle form is utilized, augmented by inwardly directed fluid (preferably air) control jets mounted at the orifice in the reentrant corrugation spaces. With the control jets turned off, the basic physical configuration of the nozzle while provided with corrugations of moderate depth produces little or no base drag and no appreciable thrust loss during cruise; yet when the added effect of the control jets is employed to deepen the corrugations, as during take-off and climb, an unexpectedly and disproportionately great reduction of noise occurs as a result of the combined aerodynamically and physically induced fluting of the jet discharge. The main drawback of this design consumes more amount of fuel for various conditions.
In US20060053767A1, the device used to reduce the jet noise the use of corrugated engine Seals for the Secondary internal divergent flaps of the nozzle. Such corrugated Seals serve not only to eliminate shock-generated noise, but also generate a counter-rotating vortices to force low Speed mixing of Surrounding ambient air with the high Speed jet exhaust. Lower exhaust velocities, combined with reduced levels of the turbulent Reynolds shear stress, lead to reduction of turbulence-generated noise, including Mach wave emission. The main drawback of this device is having variable and complex mechanism to vary the nozzle configuration.
By the analysis data collected from my invention shows no mechanism for variable nozzle as well as reduces the noise with optimized loss in exhaust velocity. Thus, there is a need for an improved corrugated nozzle device.

Summary of the invention
In light of the above mentioned drawbacks in the prior art, the present invention aims to reduce the noise level with minimum thrust loss in the Ramjet powered tip jet helicopters.
The specific objective of the invention is to reduce noise level by implementing corrugated plates at the exit of the nozzle when compared with conventional nozzle.
A further specific objective of the invention is to optimize the thrust loss for the corrugated nozzle by mixing the fluid flow from the exit of the nozzle with the atmospheric air which leads to reduce the turbulence at the exit.
Brief Description of Drawings
The invention will be described in detail with reference to the exemplary embodiments shown in the figures wherein:
Figure 1 Pictorial representation of power plant with corrugated nozzle
Figure 2 Velocity contour plot of conventional and corrugated nozzle
Detailed description of the invention
The embodiment of the present disclosure provides a corrugated nozzle which reduces noise from exit jet velocity. Corrugated nozzle was designed and analyzed based on the following criteria i.e acceptable human acoustical level.
The modeling of the corrugated nozzle is carried out using CATIA shown in figure 1 and the analysis is carried out using ANSYS CFX which is shown in figure 2. At the exit corrugated shape is provided to reduce the noise of the jet.
With reference to the figure 1 the ‘Power Plant with Corrugated Nozzle’ is provided in accordance to an embodiment of the present disclosure. Corrugated plates (4) are attached with the convergent nozzle (3) at the exit to reduce the noise level. Because of this corrugated plates, the fluid flow at the exit converges to the engine core thus reduces the turbulence level at the exit of the nozzle. Corrugated nozzle is attached with constant area duct which is termed as combustion chamber (2) to get required stagnation pressure and temperature with zero velocity as ideal condition. Inlet (1) is provided at the front of the engine with atmospheric boundary conditions as 288.15 K temperature and 1.013 bar pressure. Turbulence boundary for the inlet is considered as medium intensity and eddy viscosity ratio because of subsonic flow regime. Corrugated plates (4) are placed at the exit of the nozzle, corrugated shapes contains sharp cutting or edges to enhance the noise level reduction by increasing mixed flow with the atmosphere. Generally corrugated plates or lobe types are separate assembly which is fitted to the jet pipe (3). Nozzle area at the exit can be morphed by changing corrugated plate angle which gives provision to the constant mass flow rate at the inlet of the nozzle.
Mass flow rate to the inlet and outlet affects the exit thrust parameter, by changing the corrugated plate angle mass flow rate get affected, thus Guide vanes are fitted to the lobe-type suppressor to prevent excessive losses by guiding the exhaust gas smoothly through the lobes to atmosphere. Therefore, corrugated triangular plates at the minor axis could reduce the core length by about 80%. Therefore, the performance of corrugated nozzle is to control the elliptic jet at the exit section. But, since the blockage offered by the corrugated plate is smaller, it is advantageous from a propulsion point of view i.e. thrust loss is very negligible. Core length of the uncontrolled exit jet is five times that of exit diameter for the conventional nozzle. But, for the corrugated nozzle core length of the uncontrolled jet is one times of exit diameter which increases the mixing rate with the atmospheric air thus enhances the noise reduction. At the same time mass flow rate is slightly changed because of changing corrugated plates which affects the thrust parameter but it is negligible by increasing the nozzle area.
In accordance to an embodiment of the disclosure, the outlet (3) boundary condition for relative pressure is given as 0.95 bar which is slightly less than the atmospheric condition in order to achieve subsonic flow regime at the exit. In order to do the analysis at ideal condition, overall engine is assumed to be adiabatic insulated wall with no friction and no slip conditions. Corrugated plates (4) has plug angle of 60 downward which leads to mix the fluid flow with the atmospheric air. As a result of mixing fluid flow with the atmospheric air, turbulence level get reduces thus thrust loss of the engine is considered as negligible.
With reference to the figure 2 ‘Velocity contour plot of conventional and corrugated nozzle’ is provided in accordance to an embodiment of the present disclosure. Velocity magnitude of conventional and corrugated nozzle is analyzed under same boundary conditions. Implementation of corrugated plates affects the thrust parameter, thus velocity magnitude analysis has to be carried out for thrust performance. In this invention thrust is slightly reduced when compared to the conventional nozzle, but this thrust loss is very negligible for subsonic flow.
The following comparison of results from ANSYS CFX are made and from the result we can conclude here that insertion of hard wall corrugations on the Ramjet engine convergent nozzle exit will result in the noise reduction.
Figure 2 shows that there is a change between the hard-wall corrugated nozzle and baseline convergent nozzle in terms of pressure and thrust production. If the pressure and thrust reduces, definitely there will be reduction in the noise due to the distribution in the exhaust and also it should not affect the thrust parameter drastically. Noise level is reduced by accelerating the mixing rate and by reducing the relative velocity of jet. In velocity contour plot it is observed that thrust is reduced in optimized manner by reducing the relative velocity of jet with atmosphere, so thrust loss for corrugated nozzle is assumed to be negligible. The reduced relative velocity is clearly shown in contour plot figure2. Thus the implementation of corrugated nozzle reduces noise level with optimized thrust loss.
Thus the noise level reduction principle is to minimize the exhaust velocity of jet while still maintaining the other performance objectives.
3 Claims & 2 Figures , Claims: The scope of the invention is defined by the following claims:

Claim:
1. A corrugated nozzle ramjet engine comprising:
a) An inlet (1) has divergent area duct with constant area duct mentioned as wall (2) followed by convergent area duct called as nozzle (3).
b) In this design at the exit of the nozzle corrugated flaps (4) are installed in x- direction to mix the atmospheric air particles with the exit jet to reduce the noise.
c) In this engine atmospheric boundary conditions are given to the engine inlet (1) such as Pa and Ta.
2. As mentioned in claim 1, the corrugated nozzle engine comprising divergent flap for eliminating multi directional jet to optimize thrust loss.
3. According to claim 1, the corrugated nozzle engine is used to reduce the noise level by producing vortices at the exit of the nozzle which enhances proper mixing of atmospheric air with exit jet to lower the noise level.