Abstract: An ultrasonic flow measuring method and apparatus thereof comprises a plurality of ultrasonic vibrator apparatus mounted around the peripheral edge of a large caliber pipe at predetermined intervals, in which the ultrasonic vibrator apparatus are disposed at intervals of l=2R/(n+1) on one side radius R and at intervals of l'=R/(n+1)on the opposite side radius as well as operated in an alternating sequential arrangement in order to avoid the interference with one another, the ultrasonic vibrator apparatus are mounted on the outer wall of the pipe by being inserted into a hole of the pipe wall at a predetermined angle to the center line of the pipe, and the ultrasonic vibrator apparatus comprises a body inserted into the pipe wall; a first chamber constituted as a part of the body, for receiving an ultrasonic vibrator; and a second chamber constituted as a part of the body, for receiving a block having an acoustic resistance identical to that of the liquid flowing in the large caliber pipe to be measured, in wh

Abstract: A local river flow velocity measuring method and apparatus therefor comprises a flow velocity meter and a flow velocity measuring circuit, in which the flow velocity meter includes a plurality of ultrasonic vibrators mounted at the apexes A, B and C of a right angled triangle which sets a base AC, a vertical side BC and a oblique side AB, in which the distance of the oblique side AB is L, the height of the vertical side BC is h and an angle {(.PSI.BAC)=.PSI.} is .PSI., the propagation time of ultrasonic pulses from the apexes C to B is measured, and an angle .PSI.+.alpha. formed between the flow velocity vector V and the vertical side BC and an angle .PSI.-.beta. formed between the flow velocity vector V and the oblique side AB are indirectly measured, thereby calculating the resulting flow velocity.