高压阻塞喷注的湍流噪声

过去曾求得驻点压力（表压）在0.01到10大气压适用的喷注噪声的压力关系。现在将实验扩展到100大气压过热水蒸汽,发现低压时的关系仍然适用,不过由于喷注气体不同,此时多一个附加项20log（M₀/M）,M₀和M分别是空气和喷注气体的分子量;喷注温度则几乎无影响。于是,在与喷注方向垂直,距离喷口1米处的A声级就成为${L_A} = 80 + 20\\log \\frac{D}{{{D_0}}} + 20\\log \\frac{{{M_0}}}{M} + 10\\log \\frac{{{{(P - {P_0})}^4}}}{{{P_0}^2{{(P - 0.5{P_0})}^2}}} + 10\\log \\left {\\frac{2}{\\pi }\\left( {{{\\tan }^{ - 1}}{x_A} - \\frac{{{x_A}}}{{1 + {x_A}^2}}} \\right)} \\right]$式中D为喷口直径(mm),D₀为1mm, P和 P₀分别为喷注驻压和环境大气绝对压力,在阻塞时x_A=0.165D/D₀实验证明在较大的温度和压力范围,噪声频谱无甚差别。管道内的扰动可使噪声级提高1-6dBA,对此本文作了理论分析。低压时使 用的小孔消声器在高压下仍然有效,但应注意其特有的关系.

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 ${L_A} = 80 + 20\\log \\frac{D}{{{D_0}}} + 20\\log \\frac{{{M_0}}}{M} + 10\\log \\frac{{{{(P - {P_0})}^4}}}{{{P_0}^2{{(P - 0.5{P_0})}^2}}} + 10\\log \\left {\\frac{2}{\\pi }\\left( {{{\\tan }^{ - 1}}{x_A} - \\frac{{{x_A}}}{{1 + {x_A}^2}}} \\right)} \\right]$ 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.