Abstract: 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 l.sub.1, of base width b.sub.1 on the upstream side, and of base width b.sub.2 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 l.sub.2 and base width b.sub.3. The following dimensioning equations hold:0.1.ltoreq.b.sub.1 /D.ltoreq.0.35;0.6.ltoreq.b.sub.2 /b.sub.1 .ltoreq.0.95;0.1.ltoreq.1.sub.1 /b.sub.1 .ltoreq.0.2;0.75.ltoreq.