How does adjustable inlet guide vane affect compressor flow / head?

[CaracasEC]

Hi All,

How does adjustable inlet guide vanes affect the compressor flow/head? Could someone explain the principles? Thanks a lot guys...

 

[ortabe]

Pre-swirl will shift surge to the left. Head rise to surge will increase at the expense of maximum flow.

 

[CaracasEC]

Thanks ortabe, but could you elaborate more? how is the changing of the angle affect compressor flow/head?

 

[turb1]

Inlet guide vanes add swirl to change the incidence angle at the inlet of the impeller. With a constant speed compressor, the velocity triangle at the inlet is a function of the tip speed at the eye and the gas velocity. The angle of the blade at the inlet (Beta) is designed to minimize incidence at the design flow, at low flows the incidence angle is not optimum due to the low inlet velocity (and the blade geometry is fixed). IGV's induce swirl to reduce incidence and increase the range of the compressor. As incidence is reduced, so is head.

 

[CaracasEC]

This means that since the head develop by the compressor depends on the tip speed and gas velocity relative to impeller,at low inlet velocity the gas will pick up high energy to the impeller increasing the tangential velocity as the tip speed is constant but the relative velocity of the gas to the impeller will decrease. Also adding swirl means that the gas flow at the inlet of the impeller will be at turbulent state which will cause low flow and without swirling of the gas the gas flow at the inlet of the impeller will be laminar. Please comment on my assumptions..