Abstract:
A damping section, for an aerodynamic wind tunnel having a test section defined by a nozzle mouth at an upstream end and a collector mouth at a downstream end, is adapted to conform to a perimeter of the collector mouth and extend in the downstream end of the test section, and includes a slotted section adapted to dissipate irregularities in the flow of air at the perimeter of the collector mouth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates generally to fluid flow systems. In one of its aspects, the invention relates to the control of fluid flow in a wind tunnel system, and the elimination of extraneous noise and pressure fluctuation within a test section of the wind tunnel system.  
         [0005]     2. Description of Related Art  
         [0006]     Generally, the purpose of a wind tunnel is to measure the effect of the passage of a high velocity fluid, in this case air, over a body under controlled conditions. Such body may be an airplane, a building structure or an automobile.  
         [0007]     In a wind tunnel, the prime consideration is to be able to control the velocity and the uniformity of the air flow. One very impractical method of doing this is to have a very long straight wind tunnel with the right combination of cross-sectional area and input wind generation power. This is impractical because each end of such a wind tunnel must be open to the atmosphere. Therefore, the common practice is to make the wind tunnel a loop so that no make up air is needed, debris can be prevented from entering the tunnel, energy is conserved, and other factors, such as air temperature, can be controlled.  
         [0008]     Additionally the wind tunnel must simulate as closely as possible the wind environment that is present around the vehicle when it is moving in its natural environment. To accomplish this, wind tunnels with straight solid walls are made with very large test sections so that the vehicle under test blocks only about 5% of the cross section of the wind tunnel throat. In an open jet wind tunnel (or semi-open jet wind tunnels which have a floor surface) the tunnel can be built much smaller due to the fact that the test vehicle can block as much as 15% of the throat area without significant distortion to the air flow field around the vehicle. However, the open jet tunnel design introduces the distinct possibility that a hydro-acoustic resonance will be set up within the tunnel circuit that causes fluctuations of the velocity of the air in the test section. These fluctuations occur as various acoustic feedback paths excite the fluid field inside of the wind tunnel. The resulting unsteady flow field will no longer support appropriate aerodynamic or aero/acoustic wind tunnel testing. This is due to the fact that the aerodynamic forces vary in proportion to the velocity squared in the testing, and the noise amplitudes rise with the fifth sixth order of wind velocity. So the fluctuations must be reduced or eliminated to achieve satisfactory test conditions.  
         [0009]     The solution of this resonance has been approached from a variety of different directions. Different dimensions of the open jet wind tunnel test section and various designs of collector “flaps” have been utilized with varying degrees of success. Some of these solutions resulted in test sections that were too short for the vehicles being examined causing distortions in aerodynamic data. Other solutions isolated the resonance phenomenon to specific speed ranges, but did not eliminate it.  
         [0010]     For the purposes of aerodynamic evaluation of solid bodies, it would be advantageous to provide a wind tunnel assembly that minimizes unsteady pressure fluctuations, speed variations with time, pressure field distortions and the noise generated and attributable to the wind tunnel itself, under the entire range of operating speeds.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     An aerodynamic wind tunnel comprises a test section having an upstream end and a downstream end, a nozzle positioned near the upstream end of the test section, a collector positioned near the downstream end of the test section, and a damping section positioned in the downstream end of the test section, upstream of the collector.  
         [0012]     A damping section, for an aerodynamic wind tunnel having a test section defined by a nozzle mouth at an upstream end and a collector mouth at a downstream end, is adapted to conform to a perimeter of the collector mouth and extend into the downstream end of the test section, and comprises a slotted section adapted to dissipate irregularities in the flow of air at the perimeter of the collector mouth.  
         [0013]     In a further embodiment, the damping section comprises a top panel and a pair of depending side panels formed of a plurality of parallel slats defining the slotted section. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0015]      FIG. 1  is a plan view of a wind tunnel with a slotted damping section according to the invention.  
         [0016]      FIG. 2  is an enlarged plan view of the wind tunnel with slotted damping section Of  FIG. 1 .  
         [0017]      FIG. 3  is a side view of the wind tunnel with slotted damping section of  FIGS. 1-2 .  
         [0018]      FIG. 4  is a side view of the formation of wind vortices and reflected pressure waves in a prior art wind tunnel.  
         [0019]      FIG. 5  is a side view of the formation of wind vortices and the damping of pressure waves in a wind tunnel with slotted damping section of  FIGS. 1-3 .  
         [0020]      FIG. 6  is a perspective view of the slotted damping section of  FIGS. 1-3  and  5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     An aerodynamic wind tunnel  10  having a slotted damping section  100  according to the invention is shown in  FIGS. 1-3  and  5 . Referring with particularity to  FIG. 1 , the aerodynamic wind tunnel  10  is formed in a closed loop for environmental control of the air flow. Air flows in the illustrated aerodynamic wind tunnel  10  in a clockwise direction.  
         [0022]     Beginning with the test section  20 , the air flows into the collector  90 , then to the first corner  30  and second corner  40 , which contain turning vanes  35 ,  45 , for redirecting the air flow around each corner. From the second corner  40 , the flow of air then passes through the flow generator  50 . Flow generator  50  can comprise a fan blade/stator arrangement of conventional design.  
         [0023]     After the flow generator  50 , the flow of air then enters the third and fourth corners  60 ,  70 , with turning vanes  65 ,  75  respectively. After passing through fourth corner  70 , the air flow passes through nozzle section  80  to increase its speed to the desired test speed, at which speed it re-enters the test section  20 .  
         [0024]     Referring now to  FIGS. 2-3 , the test section  20  is defined between the nozzle  80  and the collector  90 . A test vehicle  15  is placed within the test section  20  on test section floor  22 , which can incorporate a balance or other load measuring device (not shown). Air flows in currents A from nozzle  80  through nozzle opening  82  into test section  20 . The air flows through test section  20 , around test vehicle  15 , and into collector  90 .  
         [0025]     The mouth  92  of collector  90  is conventionally surrounded with collector flaps  94 ,  96 . Collector flaps  94 ,  96  serve to funnel the air flow A into the mouth  92  of collector  90 . Referring briefly to  FIG. 4 , as the air flows out of nozzle  80  into the test section  20 , vortices V are formed, particularly proximate the edges of nozzle mouth  82 . These vortices V travel the length of the test section  20  until they impinge upon the collector flaps  94 ,  96  surrounding collector mouth  92 , or other wind tunnel structure. The collector flaps  94 ,  96  are angled outwardly to direct more air flow into the collector mouth  92 . As a result, when the vortices impinge upon the collector flaps  94 ,  96 , or other wind tunnel structure, some portion of the air flow is deflected back into the test section  20 . This reflected air sets up a harmonic, resulting in a reflected wave front P detectable as pulsations in the test section  20 .  
         [0026]     Referring again to  FIGS. 2-3 , and now to  FIG. 5-6 , a slotted damping section  100  according to the invention is positioned in the test section  20 , proximate to the collector  90 . The slotted damping section  100 , as illustrated, is formed of a plurality of slats  105 . The slats  105  are rigidly held separated from one another, in a parallel orientation, forming a gap or slot  110  therebetween. The slats  105  are banded together to form a partial box for placement in front of collector  90 . Slotted damping section  100  is formed with a top panel  120  and depending side panels  115 . The generally straight top and side panels  115 ,  120  are formed to conform to the perimeter of collector mouth  92 , although it is anticipated that the profile of the damping section  100  can be arcuate. It is also anticipated that the slotted damping section  100  can be formed of a solid panel or panels, with slots  110  cut or formed therein.  
         [0027]     Referring to  FIG. 5 , the vortices V traverse the test section  20  and encounter the slotted damping section  100  before they impinge upon the collector flaps  94 ,  96 , or other wind tunnel structure. When the vortices V encounter the slotted damping section  100 , the vortices V are dissipated. The vortices V are thereby weakened before impinging upon the collector flaps  94 ,  96 , or other wind tunnel structure. As a result, the weakened vortices V do not strike the collector flaps or other wind tunnel structure with sufficient magnitude to form a wave front P that is reflected back into the test section  20 . The pulsations associated with the reflected wave front P are thereby eliminated, aiding in the development of more accurate aerodynamic and acoustic data in the evaluation of test vehicle  15 .  
         [0028]     While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the scope of the appended claims.