Turbo Charger Design: Compressor and Turbine Blades

[DJM111188]

Hello can anyone please provide me with some insight about turbo charger design? Specifically referring to the compressor and turbine blades? My inquiry is more directly aimed at the number of blades. On different turbos they use different numbers of blades and I'm wondering if a higher number of blade offers any better performance over a identically configured turbo with a lower number of blades.

I have attached 3 images below. The first being a compressor side with a high number of blades, the second being a compressor side with a low number of blades, and the third being a turbine side with a high number of blades. It is important to note that the turbine side of a turbocharger is universally equipped with a high number of blades.

I would assume that a higher number of blades would provide a more uniform flow whereas a lower number of blades would provide more of a relatively pulsed flow. Also I would assume with all variables being equal between 2 turbos and only the number of blades being changed, that the turbo with the higher number of blades would provide more air flow.

I am no where near an expert and I hope someone with some knowledge will enlighten me. I thank you dearly for your time.

 

[jack action]

Simple answer: No. When you design turbomachinery, you must not think in terms of a succession of blades but in a succession of "ducts" (the blade being the walls that separates those ducts).

The duct's shape change the directions of the air going through it and that's what puts energy in the air (compressor) or removes it (turbine).

the angle of the blades are dependent of the rotational speed of the turbine, the inlet velocity of the air and the pressure ratio we want to achieve. If the found angle to design the blade is very large (like in your 2nd picture) the blades will be very close together, hence you will need less of them to create the "perfect" width for your ducts. If you take the 2 extreme cases of the blades having an initial angle of 0° and 90° with respect to the flow, in the first case the width of the duct is the distance between 2 blades and in the second case the width will be zero since all blades are perpendicular to the flow.

 

[mender]

I'm pretty sure that if you look closely at the second picture, you'll see that the impeller has twelve blades. There is a shorter blade between each of the visible (from the top) blades.

 

[DJM111188]

I'm pretty sure that if you look closely at the second picture, you'll see that the impeller has twelve blades. There is a shorter blade between each of the visible (from the top) blades.

You are correct. Many compressor wheels are made in that fashion. I was more concerned with the surface area relative to more blades then the actual amount of them.

 

[Turbodog]

Another consideration is that the more blades there are, the less area there is to pass flow through. The more walls that divide up the flow, the more frictional areas there are.