Abstract:
A noise generator system is provided with each noise generator being pivotally mounted to a mounting surface associated with the air intake of a turbineless jet engine. Each noise generator is positioned so as to convert a laminar or transitional air stream into a turbulent air stream such that a turbulent air-fuel mixture is realized in the combustion section of the engine to achieve more efficient operation.

Description:
DEDICATORY CLAUSE 
     The invention described herein may be manufactured, used and licensed by or for the U.S. Government for governmental purposes without payment of any royalties thereon. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention pertains to jet engines having no rotary compressor. More particularly the present invention pertains to a device for creating turbulent fluid flow into the combustion chamber or region of such a jet engine. 
     II. Discussion of the Background 
     A ramjet is a type of jet engine which includes an air inlet, combustion chamber and exhaust nozzle. The air inlet is designed to accommodate air moving at a supersonic speed. An inlet cone or body is situated within the air inlet and constricts air flow such that the received air is compressed and slows to a subsonic speed before entering the combustion chamber. For liquid-fuel type ramjets, the combustion chamber is provided with fuel injectors and flaming elements for combusting an air-fuel mixture. The combusted air-fuel mixture is then expelled through the exhaust nozzle to achieve propulsion. The ramjet has no moving parts and some have referred to it as resembling a stovepipe-type of hardware. 
     As previously indicated, to perform efficiently, the ramjet requires air to be input at supersonic speeds. Therefore, a ramjet-powered air vehicle must have an alternate engine or power source to initiate speeds which are sufficient in magnitude to effectively switch propulsion responsibilities to the ramjet. 
       FIG. 1  is a side-view cross-section of an exemplary cylindrically-shaped ramjet engine. The ramjet  10  has an inlet  12  for receiving inlet air  14  which preferably enters the inlet at a speed in excess of Mach 1. The shape of inlet cone or body  16  directs the inlet air  14  to a constricted flow path  18  which is formed by the ramjet casing  20  and the inlet body  16 . 
     Upon exiting the constricted flow path  18  the inlet air enters the combustion chamber  22  which is provided with fuel injectors  24  located proximate to flaming elements or burners  26 . Fuel exiting from the fuel injectors mixes with the compressed inlet air and the air-fuel mixture is combusted by the burners  26 . The combusted air-fuel mixture exits as exhaust from exhaust nozzle  28 . 
     A scramjet or supersonic combustion ramjet is similar in design to a ramjet. However, the airflow in the combustion chamber of a scramjet is supersonic. Accordingly, the air inlet of a scramjet is designed to allow compressed, supersonic airflow to continue into the combustion chamber. 
       FIG. 2  is a side-view cross-section of an exemplary cylindrically-shaped scramjet engine. The scramjet  30  is provided with a casing  32  within which is situated a center body  34  having an inlet region  36 , a combustion region  38  and an exhaust nozzle region  40 . An inlet  42  is formed from the inlet region  36  of center body  34  and the forward region  32 F of casing  32 . The center body  34  is contoured to form a constricted flow path  44  with the casing  32 . 
     Within the constricted flow path  44  is a combustion section  46  which includes (in the liquid fuel-type scramjet) fuel injectors  48  in proximate relation to burners  50 . The combusted air-fuel mixture exits the scramjet through the nozzle  52  which is formed from the exhaust nozzle region  40  of the center body  34  and the rearward portion  32 R of casing  32 . 
     The National Aeronautic and Space Administration (NASA) has invested heavily in scramjet technology. NASA&#39;s X-43A scramjet has been flown at a speed of Mach 9.6 and utilized a Pegasus booster rocket to achieve the hypersonic speeds necessary to initiate scramjet propulsion. Experiments with scramjets have resulted in a belief that the technology will eventually lead to hypersonic commercial aviation. 
     A problem encountered in the high speed environment of the scramjet has been the inability to efficiently mix air and fuel for optimal combustion. In aeronautics, it has been a typical design goal to achieve laminar airflow over as much of a wing or vehicle surface as possible. (Air that flows smoothly in a continuous stream is laminar, while an air stream that is rough or broken is turbulent. Transitional airflow, as the name implies, alternates or transitions between laminar and turbulent conditions.) 
     In the prior art, the airflow received in the combustion chamber or combustion section of a SCRAMJET has been laminar or transitional in nature which has resulted in less than optimal mixing and combustion. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to make a SCRAMJET more efficient. 
     Another object of the present invention is to improve SCRAMJET reliability and safety. 
     These and other valuable objects are realized by a system for creating turbulent airflow in a combustor section of a type of jet engine not having a rotary compressor (i.e., a turbineless engine). The system includes a mounting surface or platform and at least one noise generator connected to the mounting surface. The noise generators are positioned forward of the combustion section for purposes of converting an air stream (which is laminar or transitional) into a turbulent air stream. The turbulent air stream reaches the combustion section at a supersonic speed. The noise generators are pivotally attached to the mounting surface. The noise generators are wedge-shaped with each having a top and a bottom through which a pivot pin extends so that each noise generator can move or rotate back and forth on the mounting surface (in directions lateral to the incoming air stream). 
     A plurality of noise generators can be spaced apart on the mounting surface. Each noise generator of the plurality of noise generators is pivotally connected to the mounting surface. Each of the noise generators has a pivot pin which extends through the noise generator and is offset from a center line of the noise generator such that the pivot pin does not contact the center of mass of the respective noise generator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is side-view, longitudinal cross-section of an exemplary ramjet engine. 
         FIG. 2  is side-view, longitudinal cross-section of an exemplary scramjet engine. 
         FIG. 3  is a schematic view of the acoustic noise-generation system of the present invention. 
         FIG. 4  is an x-ray perspective view of an acoustic noise generator according to the present invention. 
         FIG. 5  is a perspective view of an acoustic noise generator of the present invention which demonstrates that the pivot-pin aperture in the acoustic noise generator is offset from a center line. 
         FIG. 6  is a plan view of an acoustic noise generator according to the present pivotably mounted to a support surface. 
         FIG. 7  is an exemplary illustration of the velocity distribution of laminar airflow in a pipe. 
         FIG. 8  is an exemplary illustration of the velocity distribution of turbulent airflow in a pipe. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 3 , the air intake or inlet  421  of a scramjet engine (having an inlet, combustion region and exhaust nozzle) is attached to a mounting surface or support deck  60 . Supersonic laminar airflow is indicated by arrows  62  which are aligned with inlet  421 . Placed forward of inlet  421  are a plurality of acoustic noise generators or elements  64 A,  64 B,  64 C,  64 D. 
     Each acoustic noise generator  64  is attached to mounting surface  60  for the purpose of creating a turbulent airflow  66  to be received by the combustion section of the engine. The mounting surface  60  can be a part of the fuselage or skin or an air vehicle, or can be a properly contoured extension of the scramjet&#39;s casing which extends forward of the air intake region, or can be an appropriate structure which allows the acoustic noise generators to be mounted in the airflow path forward of the combustion section of the scramjet. 
     Each acoustic noise generator  64  is wedge-shaped. The x-ray perspective view of  FIG. 4  demonstrates that the noise generator element  64  has a triangular-shaped top  64 T and a triangular-shaped bottom  64 B with three rectangular sides  64 S 1 ,  64 S 2  and  64 S 3 . The acoustic noise generator has an aperture which extends from its triangular-shaped top  64 T through its triangular-shaped bottom  64 B to accommodate a pivot pin  68 . The pivot-pin  68  has heads or caps on both ends which are greater in diameter than the shaft of the pivot-pin to allow the pivot pin  68  to be firmly secured to the mounting surface  60 . Other securing techniques known in the art are acceptable. As such, each noise generator  64  is pivotably mounted to the mounting surface  60 . The use of a small sealed bearing can be used to reduce friction between the pivot pin and noise generator. 
     In  FIG. 5 , the pivot pin aperture  70 , in accordance with the teachings of the present invention, is offset from center line  72  of the noise generator  64 . Accordingly, the pivot pin  68  does not extend through the center of mass of the noise generator  64 . 
     The offset causes each noise generator  64  to rotate back and forth due to the air stream flowing over the air inlet area. The kinetic energy of the air vehicle results in the rotation of the noise generators so no drive mechanism or power is required for noise generator movement. To keep the drag values low, each noise generator is sized to remain within the boundary layer flow, i.e. the layer of airflow aligned with the air inlet. 
     The airflow conditions typically found at an altitude above 30 km and above Mach 10 are such that the air is laminar to transitional in nature. Such conditions reduce the mixing capacity of the air-fuel mixture to be combusted. In the present invention, the back and forth rotation of the noise generators causes the airflow entering the combustion section of a scramjet to be fully turbulent with an increased Reynold&#39;s Number. 
     Since the airflow through a scramjet engine is supersonic, little time exists to combust the air fuel mixture. Making the airflow in the combustor section fully turbulent dramatically enhances the mixing of air and fuel and significantly improves the efficiency of the scramjet engine. 
     This enhanced performance of the engine can be explained to some degree by reference to  FIGS. 7 and 8 . 
     In  FIG. 7 , laminar air flow in pipe  80  results in a parabolic velocity curve  84  with the vertex of the parabola touching a cross section  82  of the pipe. Thus, the fastest traveling air which is small in concentration or density is located at the center of the pipe. 
     The great bulk of the laminar air flow in  FIG. 7  travels at a lesser speed in parabolic distribution behind the vertex. If it is desired to combust an air fuel mixture traveling at supersonic speed along section  82 , it is apparent that inefficiencies would result. 
     In  FIG. 8 , a turbulent flow of air traveling in pipe  80  has a velocity curve  86  which is relatively flat or planar with cross section  82 . If an air-fuel mixture is combusted at selected locations at cross section  82 , the efficiency of combustion of the air fuel mixture will be significantly improved over the situation found in  FIG. 7 . 
     The teachings of the present invention allow for more efficient and safer operation of a scramjet engine. 
     Various modifications of the present invention will be possible to those of skill in the art. Accordingly the scope of the invention is limited only by the claim language which follows hereafter.