Method and apparatus for measuring unsteady flow velocity

Measuring apparatus for measuring the velocity of a fluid having an unsteady flow, in a duct, wherein the apparatus comprises:

• a) two first pressure taps (14, 16;
• 25, 26;
• 35, 36;
• 45, 46;
• 51, 57) provided on a cylindrical portion of the duct, said two first pressure taps being spaced apart over said portion in a direction that extends parallel to the flow so that said two first pressure taps measure respective static pressures on two locations spaced apart parallely to the flow;
• b) a third pressure tap (18;
• 37, 47, 58) provided inside the duct, in a location of said duct having a cross-section which is different than said cylindrical portion,
• c) means for comparing the output signals of said two first pressure taps (14, 16;
• 25, 26;
• 35, 36;
• 45, 46;
• 51, 57);
• d) velocity measuring means for defining a measurement of the fluid velocity at instants when said comparing means detects that said output signals of said two first pressure taps are equal;
• e) change determining means for determining changes in the velocity between instants where said output signals of said two first pressure taps are equal, by numerically integrating the difference between said two static pressures signals issued by the two first pressure taps;
• and
• f) velocity determining means for determining the fluid velocity between instants where said output signals of said two first pressure taps are equal by summing the fluid velocity measured by said velocity measuring means at instants where said output signals of said two first pressure taps are equal, and the changes of velocity determined by said change determining means.