HIGH PRESSURE EXTENSION OF CHOKED JET TURBULENT NOISE THEORY

A formula of pressure dependence for the turbulent noise of a cold air jet has been derived previously, holding for stagnation pressures （gauge） between 0.01 and 10 atmospheres. Experimental measurements are extended to a hundred atmospheres for superheated steam jets. It is found that the formula expressed in terms of pressures holds also in the wider range, and the jet material may be accounted for by an additional term 20log（M₀/M）, where ,M₀ and M are the molecular weights of the air and the jet material, resp., and the jet temperature has little effect. As a consequence, the A-weighted sound level L_A produced by a jet at 1 meter from the nozzle and 90° from the jet axis is shown to be L_A = 80 + 20\log \fracDD_0 + 20\log \fracM_0M + 10\log \frac(P - P_0)^4P_0^2(P - 0.5P_0)^2 + 10\log \left \frac2\pi \left( \tan ^ - 1x_A - \fracx_A1 + x_A^2 \right) \right where D is the nozzle diameter in mm,D₀ is 1 mm, P₀ and P the ambient and jet stagnation pressures （absolute） resp., and for choked jets X_A = 0.165D/,D₀. It is also shown that the noise spectrum changes little with the temperature and stagnation pressure. Disturbance inside the pipe may make an addition to the noise level of 1-6 dBA, depending on the valve conditions. The micropore mufflers used, at low pressures are effective also at high pressures, with due considerations of diffusion properties.