Aerodynamic noises

High hydrogen gas velocities in piping increase turbulence and pressure drop, contribute to excessive sound pressure levels (aerodynamic noise), and can cause internal piping erosion. Acoustically induced vibration in the piping shall be avoided at all times. 

In special cases such as multiple valve installation, the aerodynamic noise level may warrant more detailed determination. However, this is a decision of the system designer familiar with all the local conditions and regulations and, more importantly, implantation of the valves within the site. 

Section 3 Control valve aerodynamic noise prediction method... 

Powell, A. (1960). Aerodynamic noise and the plane boundary. J Acoustical Society of America, 32 982-990. 

The noise sources in control valves include mechanical vibration (usually below 100 dBA) hydrodynamic noise caused by liquid turbulence, cavitation, or flashing (usually below 110 dBA) and aerodynamic noise (can reach 150 dBA). In control valve design, aerodynamic noise can be a major problem. Aerodynamic noise generation, in general, is a function of mass flow rate and the pressure ratio (p /pf) across the valve. The point at which sonic speed is reached in the valve vena contracta is a function of the valve design. 

AERODYNAMIC NOISE - Also called generated noise, self-generated noise is noise of aerodynamic origin in a moving fluid arising from flow instabilities. In duct systems, aerodynamic noise is caused by airflow through elbows, dampers, branch wyes, pressure reduction devices, silencers and other duct components. 

Such flat surfaces are very effective to reduce the running noise in the ICE train because almost aU the noise is only due to aerodynamic noise at a speed of 300 km/h. 

Turbulent or unbalanced media flow (i.e., aerodynamic or hydraulic instability) does not have the same quadratic impacts on the vibration profile as that of load change, but it increases the overall vibration energy. This generates a unique profile that can be used to quantify the level of instability present in the machine. The profile generated by unbalanced flow is visible at the vane or blade-pass frequency of the rotating element. In addition, the profile shows a marked increase in the random noise generated by the flow of gas or liquid through the machine. 

The power required to overcome tire friction and aerodynamic drag is irreversibly lost, mainly as heat and noise, cannot be recovered and can be estimated from the following empirical relations ... 

The facility of small volume production in RPs by hand lay-up led quickly to the use of these materials for van and truck bodies. Today, however, numbers have built up to justify press-molding many panels in SMC. Lighter weight and improved aerodynamics (reducing fuel costs), with lower maintenance, reduction in noise and overall improvement in comfort have been the reasons. 

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