OCR Text |
Show - 6 - where f3 is a constan t, and the unit of P is P a. The sound pressure is propors tional to the 1.65th power of S u . The measured values of P below 2 kHz are plotted against the logarithms of s flow velocities in the range of f < 2 kHz and the results are shown in Fig. 6. These data were of turbulent premixed flames at <p = 1.0 and 1.4 and without flame. In these cases, P s increases_ w ith U. The gradien ts of the line representing average variation of P with log( U) with flame are slightly larger than 25 dB of s that without flame and can be expressed as S pi = ( + 281og( U), (4) where U is the mean flow velocity in cm/s, and ( is a constant. The sound pressure is proportional to the 1.4 th power of U. SOUND PRESSURE[9] The pressure P f su pported by a flame fron t is known to be given as [5], (5) where p and U are the density and velocity of gas relative to the flame front, respectively. The subscripts, u and b represent unburned and burned, respectively. The total flame surface area A and total mass flow rate Q should be correlated as (6) where d is the burner diameter. If a fraction £ of the total flame front area A is the area effective to emit sound, the total rmitt d sound energy I would be s gIven as |