Abstract Disclosed are a method and apparatus for determining a quantity related to relative movement between a fluid and a body in the fluid around which the fluid divides. The relative flow past the body produces the von Karman phenomenon, wherein flow past an obstruction causes periodic fluid disturbances in the form of vortices that are shed alternately from opposite sides of the obstruction to form what is known as the Karman Vortex street in the wake of the obstruction. It should be understood that Karman vortices and related fluid disturbances are referred to as being ''''periodic'''' although they are not perfectly periodic; they are nearly periodic and have an average period. As each vortex is formed, the flow shifts somewhat from one side of the obstruction to the other producing periodic fluid disturbances in the form of fluid oscillations just ahead (upstream) of the obstruction. Spaced acoustic signals are propagated across the fluid path just ahead of or behind the object and the frequency of fluctuations in the travel time of the acoustic signals due to the von Karman related disturbances are detected as a measure related to the relative movement between the fluid and the object. Such a measure may for example be velocity of the relative movement e.g. speed of a boat, velocity of fluid through a conduit, volume of fluid flow, etc.
An apparatus for measuring the velocity of relative movement in a direction of displacement between a fluid and a body immersed therein, the cross-section of said body being such that fluid disturbances varying at a frequency characteristic of said velocity are created in a zone extending in front and in the wake of said body, said apparatus comprising: a pulse generator having a constant repetition rate; transmitting transducer means energized by said pulse generator for directing acoustic signals at said constant repetition rate across said zone at an angle to said direction of displacement; receiving transducer means responsive to said transmitted acoustic signals after modulation by said disturbances in said zone; means responsive to said transmitting transducer means and to said receiving transducer means for deriving amplitude signals representing respective time intervals, each time interval being defined between the transmision of one of said acoustic signals by said transmitting transducer means and the reception by said receiving transducer means of a corresponding one of said transmitted acoustic signals; and means responsive to said amplitude signals for detecting a frequency signal characteristic of fluctuations in the amplitude of said amplitude signals said frequency signal being representative of said velocity.
Claim 2
Independent Claim
198 words
An apparatus for measuring the velocity of relative movement in a direction of displacement between a fluid and a body immersed therein, the cross-section of said body being such that fluid disturbances varying at a frequency characteristic of said velocity are created in a zone extending in front and in the wake of said body, said apparatus comprising: a pulse generator having a constant repetition rate; transmitting transducer means energized by said pulse generator for directing acoustic signals at said constant repetition rate across said zone at an angle to said direction of displacement; receiving transducer means responsive to said transmitted acoustic signals after modulation by said disturbances in said zone; means responsive to said transmitting transducer means and to said receiving transducer means for deriving amplitude signals representing respective time intervals, each time interval being defined between the transmision of one of said acoustic signals by said transmitting transducer means and the reception by said receiving transducer means of a corresponding one of said transmitted acoustic signals; and means responsive to said amplitude signals for detecting a frequency signal characteristic of fluctuations in the amplitude of said amplitude signals said frequency signal being representative of said velocity.
Claim 3
Dependent Claim
18 words
An apparatus according to claim 1 with said detecting means including filter means for extracting said frequency signals.
Claim 4
Dependent Claim
23 words
An apparatus according to claim 2 with said detecting means further including a frequency indicator responsive to the output of said filter means.