How fast do turbo wheels spin? Do they ever exceed the speed of sound?

[Rafs-T-Type]

So some reading suggests that turbos spin around 100,000 RPM, but some double that. Keep in mind I didn't find these numbers from a manu or a scientist so they could be BS for all I know. But that got me thinking...at that speed are they surpassing the speed of sound? So I did a little math base on a 65MM wheel... which is about 2.5". Circumference = 7.85" x 100,000rpms = 785,000 inches per minute/12 = 65,416 feet per minute/5,280 = 12.39 miles per minute * 60 = 743 MPH Speed of sound is 767MPH. That's awfully close. A little more RPM or wheel size and it's there. Is it possible it exceeds it sometimes and the turbo eats itself?

Thoughts?

 

[No disintegrations]

I think 100,000 is high for that size turbo and 200,000 rpm is prob some tiny thing for a mini cooper. My guess is they are not supposed to exceed sound barrier. Just as an aircraft propeller should not.

 

[~JM~]

I believe the speed of sound varies due to ambient conditions, such as temperature, pressure, or vacuum.

Shaft speed on a turbine powered generator is usually 3600 RPM. The tips of the turbine blades are traveling much faster.

 

[Nigel]

I would be surprised if the relative mach number exceeded 1 in an industrial gas turbine. Stress, vibration, and noise would be considerably higher than subsonic. The absolute tip speed is higher than the speed of sound at sea level in air, but the resultant velocity vector across the airfoil I would think would be less, maybe wrong. Additionally, the compression process would be much less efficient in the trans-sonic or supersonic range. As the temperature and pressure rise, so does the speed of sound. Even if you had supersonic tip speeds in the first couple of stages, I am guessing you would not in the remaining stages. I would think a centrifugal compressor would be very inefficient if tip speeds exceeded the speed of sound. A lot of heat would generated, along with a lot of stress and vibration.

 

[Rafs-T-Type]

Just gonna throw this in there...from precision "This is all dependent on the application and turbocharger size, we however see our product have a shaft speed of anywhere from 60,000rpm to 211,000rpm in real world applications."

 

[No disintegrations]

That's good info but we would need diameter AND rpm to find the tip speed. I would still bet the 200,000 rpm units are super small used in small engines like personal watercraft or etc.

 

[Rafs-T-Type]

That's good info but we would need diameter AND rpm to find the tip speed. I would still bet the 200,000 rpm units are super small used in small engines like personal watercraft or etc.

I agree. I simply asked them what speed their wheels spin. I just wanted to say those speeds aren't just a blogger guess anymore, they came straight from the horses mouth.

I've also found that the speed of sound variates with pressure so we would need to know that part of the equation too. I'm going to see how much that plays into the equation at a later time, when I have some time.

 

[Nigel]

You have to also take into account that the air is moving through the wheel, the wheel also has swept tips. It is the not the absolute velocity, but the velocity of the air relative to the compressor blades.