text: In metrology, specifically axial-flow turbine meters, the Strouhal number is used in combination with the Roshko number to give a correlation between flow rate and frequency.  The advantage of this method over the frequency/viscosity versus K-factor method is that it takes into account temperature effects on the meter.
  where,
  : f = meter frequency,
  : U = flow rate,
  : C = linear coefficient of expansion for the meter housing material.
  This relationship leaves Strouhal dimensionless, although a dimensionless approximation is often used for C, resulting in units of pulses/volume (same as K-factor).
  This relationship between flow and frequency can also be found in the aeronautical field. Considering pulsating methane-air coflow jet diffusion flames, we get
  where,
  : a = fuel jet radius
  : w = the modulation frequency
  : U = exit velocity of the fuel jet
  For a small Strouhal number (St=0.1) the modulation forms a deviation in the flow that travels very far downstream. As the Strouhal number grows, the non-dimensional frequency approaches the natural frequency of a flickering flame, and eventually will have greater pulsation than the flame.