Search found 11 matches

by Hermann.Rochholz
Sat Aug 04, 2018 6:34 am
Forum: Airfoils
Topic: Reynolds number of the airfoil data
Replies: 5
Views: 11127

Re: Reynolds number of the airfoil data

Take care with this machine: I read: Rated Power at 11.4 m/s and 5MW. This means a cp of 0.442. If it is a gearbox machine it is extremely questionable. IMO impossible. 0.442 can be maybe the optimum cp- but at RP the TSR drops and one will get maybe 0.40. OK- if the machine rotates with a tip speed...
by Hermann.Rochholz
Mon Jul 16, 2018 4:06 am
Forum: Airfoils
Topic: The airfoil of AWT-27
Replies: 3
Views: 6791

Re: The airfoil of AWT-27

I searched for AWT-27 and I found that: https://github.com/NREL/HARP_Opt/tree/master/Source/WT_Perf/v3.05.00a-adp/CertTest/Airfoils on GitHub (Thanks for putting WT_Perf Code there). Therefore I assume this airfoil is not a single airfoil; it's in fact an interpolation of this series of NREL S8XX ai...
by Hermann.Rochholz
Wed Jul 04, 2018 5:41 am
Forum: Airfoils
Topic: New set of Airfoils for Small WT
Replies: 0
Views: 9499

New set of Airfoils for Small WT

Hallo!

I've designed a series of airfoils for small WTs since I was not satisfied by the existing ones.
I've made also a machine layout with them ending up in a conservative cp=0.450 of the rotor (TSR of only 6!).
It's an xfoil-calc.
Critical comments welcome.

Hermann R.
by Hermann.Rochholz
Sat Feb 11, 2012 4:31 am
Forum: Rotor Aerodynamics
Topic: Hub Losses
Replies: 7
Views: 12994

Re: Hub Losses

Hello and thank you. Here's the original article where It's derived - I found it (but bought it 4 month ago): http://goedoc.uni-goettingen.de/goescholar/handle/1/6356 Prandtl, Ludwig; Betz, Albert (2010): Vier Abhandlungen zur Hydrodynamik und Aerodynamik - In: Dillmann, Andreas (Ed.) Göttinger Klas...
by Hermann.Rochholz
Sat Feb 11, 2012 4:05 am
Forum: Airfoils
Topic: Wanted: University to predict airfoil coefficients
Replies: 4
Views: 8378

Re: Wanted: University to predict airfoil coefficients

Hello Marshall! A comment: 1) I think it's well known that "the old" Eppler code predicts airfoil performance too optimistic. xfoil is here better. There are several publications on the internet which show that. Nevertheless, checking out measurement results with xfoil tell that it's a lit...
by Hermann.Rochholz
Mon Jun 27, 2011 1:29 pm
Forum: Airfoils
Topic: cA and cW calculation from airfoil data
Replies: 8
Views: 10713

Re: cA and cW calculation from airfoil data

Hallo Marshall! Why? Hmm- Several years ago I read an open vacancy. One person was searched for this open position. This person should make wind tunnel tests, write the evaluation programs and by the way should make CFD-calculations. Therefore it must be very easy to find the correct data :) Hermann...
by Hermann.Rochholz
Sat Jun 04, 2011 8:54 am
Forum: Rotor Aerodynamics
Topic: Hub Losses
Replies: 7
Views: 12994

Re: Hub Losses

Dear Jason!

Thank you for your answers. Only to to clarify my opinion:
"My" formula would be symmetric to the tiploss.
I am aerodynamicist, but that is IMO math.

Kind regards
Hermann

I ordered already the reprints of Prandtl and Betz-
maybe this will clarify the stuff.
by Hermann.Rochholz
Wed Jun 01, 2011 1:58 pm
Forum: Airfoils
Topic: cA and cW calculation from airfoil data
Replies: 8
Views: 10713

Re: cA and cW calculation from airfoil data

Hallo! All the results based on "the old" eppler code provide too good results. That means that especially the Reynolds-sensitivity is underestimated. This was shown especially at the model airfoils of eppler, which were all not good- this was measured in Stuttgart obout 20 years ago. This...
by Hermann.Rochholz
Wed Jun 01, 2011 6:17 am
Forum: Rotor Aerodynamics
Topic: Hub Losses
Replies: 7
Views: 12994

Re: Hub Losses

Dear Jason. Yes, we are talking about eq. 13. But I read here (B/2) * (r-Rhub)/ (r sin(phi)) . Version January 2005- is my paper here the wrong one? Lets check symmetry for the tip and hubloss. and take r/R= 0.1 for the hubloss and r/R)=0.9 for tiploss and Rhub=0. And assume 2 blades. Then f= 0.1111...
by Hermann.Rochholz
Fri May 27, 2011 5:15 pm
Forum: Airfoils
Topic: Airfoils on a 5m Diameter Turbine
Replies: 4
Views: 7793

Re: Airfoils on a 5m Diameter Turbine

Hallo! This is not so easy. What's missing: -Tip speed ratio - Reynolds number - Blade materal (e.g. if you have only low torsional stiffness you should use an airfoil with low pitching moment) - This tip airfoil will break down as a first result below ~ RE= 600000. ( I took Xfoil and half Reynolds ...
by Hermann.Rochholz
Fri May 27, 2011 12:44 pm
Forum: Rotor Aerodynamics
Topic: Hub Losses
Replies: 7
Views: 12994

Hub Losses

Hub loss: 1) In all manuals hub correction exponent (see e.g. Aerodyn Man p. 6) is described as f = (B/2) * (r-Rhub)/ (r sin(phi)) . But isn't it f = (B/2) * (r-Rhub)/ ((1-r)* sin(phi)) ? One can easy check it out if Rhub is set to zero and the value is set for .1 at the hub or at .9 at the tip. Tha...

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