To create vortex flow sensors with an extended range of constant Strouhal number toward small Reynolds numbers, with a small variation of the vortex separation frequency, and with precise calculability of the Strouhal number in the range of a constant volumetric-flow-rate/vortex-separation-frequency ratio, a drag body is provided which is permanently connected with the internal wall of a fluid-conducting measuring tube of inside diameter D, or fixed in a frame set in the measuring tube, at diametrically opposed points, and which consists of an upstream-side flat trapezoidal part of length l1, of base width b1 on the upstream side, and of base width b2 on the downstream side, and a wake part adjoining the trapezoidal part without a gap and having a cross section in the form of a triangle of length l2 and base width b3. The following dimensioning equations hold:0.1/=b1/D/=0.35;0.6/=b2/b1/=0.95;0.1/=11/b1/=0.2;0.75/=12/b1/=1.5;0.5xb2/b1/=b3/b1/=b2/b1.
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