Understanding HTHS

[Shannow]

The unbalance is the 1x that I mentioned (that's 1x the operating speed). With an unbalance, in a bushing like a turbo (well like the turbines as well), that means that the thin point on the wedge is moving around as the whole gig tries to rotate about it;s centre of mass.

The measurement is actual shaft displacement, peak to peak...shouldn't ever be more than around half the total clearance.

If the shaft were not rotating, and being positioned in exactly the same spots a few hundred thousand times per minute (if you can visualise that), viscosity would definitely "damp" that motion, through things like the squeeze film effect.

In real life, there's the hydrodynamic "stiffness" overlaid with the static case. So in the area of stability, definitely. In the area of instability definitely not, and if close to the transition, it could tip things over.

 

[4wd]

By “stiffness” … something like how speed across water supports someone on a ski?

 

[OVERKILL]

Originally Posted By: ZeeOSix
There are all kinds of turbocharger bearing designs (search the 'net), but many are journal/sleeve type so I'd think there is hydrodynamic lubrication going on there. Considering how fast the turbo shaft spins (up to 300K) I'd say there's lots of oil hydrodynamic shearing going on.

http://www.turbos.bwauto.com/products/turbochargerBearingSystem.aspx


Be curious to see what Honda is using, eh?

 

[PimTac]

Thanks for the answers to my inquiry.

 

[Shannow]

Originally Posted By: 4WD
By “stiffness” … something like how speed across water supports someone on a ski?


I don't like the analogy, as that's more of an inertial effect rather than viscosity, but it's probably close enough .

 

[Shannow]

Originally Posted By: JAG
Thanks Shannow. In another paper I read yesterday, it said that since no turbo is perfectly balanced, its rotor will gyrate and the oil film helps damp that motion. Higher viscosity increases the damping. Is that captured in the stability vs speed and Sommefield number, or is it a totally separate phenomena?


Here's a paper that explains some of it.

http://rotorlab.tamu.edu/me626/Notes_pdf/Notes04 Static Load JBs 10.pdf

 

[JAG]

Thank you, Shannow! There are a lot of finger paintings in there.

 

[alcyon]

Originally Posted By: Gokhan
Originally Posted By: Shannow
Originally Posted By: 1JZ_E46
Agreed. I would say both KV100 and HTHS play a roll. For example, KV100 would be a better indicator as to the volume of oil pumped through the piston oil squirters for a given temperature.

Squirters are pressure/density, with limited viscosity impact.

Did a thread on that a while back, using some actual figures.

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4175771/Re:_Nozzle_Flow_Versus_Pressur

Will have to fix the Photobucket mess-up over the weekend.

Photobucket has ruined the Internet for many. It's a shame.

I use Google Photos. Use a public album and append ?.jpg or ?.png etc. to the image link and you can then post the image here and other Web sites.

Yeah, since the laminar-flow rate through the nozzle goes as P_gauge/viscosity and P_gauge increases with viscosity for small to moderate RPMs in normal operating temperature, I would think that the nozzle flow would be roughly independent of the viscosity, as viscosity cancels out in numerator and denominator. However, the output nozzle speed will get a boost from the gauge pressure due to Bernoulli's principle: Output nozzle speed squared = Input nozzle speed squared + 2 x gauge pressure / density.

Quote:
Will have to fix the Photobucket mess-up over the weekend.

You mean you will pay the $400 ransom or you'll do what your Aussie pal Mel Gibson did in the so-named movie?

There is a fix for photobucket right on this site.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4554636/1

 

[Primus]

Originally Posted By: JAG
Thanks Shannow. In another paper I read yesterday, it said that since no turbo is perfectly balanced, its rotor will gyrate and the oil film helps damp that motion. Higher viscosity increases the damping. Is that captured in the stability vs speed and Sommefield number, or is it a totally separate phenomena?


Higher viscosity/HTHS should also better protect against eventual hard contaminants and higher the oil thickness, they higher in size contaminants may pass through without damaging surfaces.