[Solareclipse]

Hi folks,
i´d like to ask a few questions on how to properly use the Mises code in order to investigate the surface velocity distributions in a 2D turbine cascade. I have trouble finding sufficient information in the manuals of Mises to fully understand how the input files should be set up. Maybe there is somebody here who has a lot of experience in using Mises and who could even help me via private messages or via email?

I´ll state the questions here anyway so that you have an idea what it is about:
I want to investigate the "historical" Nasa Energy Efficient Engine E3 Low Pressure Turbine, built by Pratt&Whitney in the 1980´s. The technical data is accessible here https://ntrs.nasa.gov/archive/nasa/c...9840020720.pdf

First i want to look at the Inlet Guide Vane at the Mean Section.
The Inlet total pressure, Inlet total temperature, Inlet Gas Angle, Inlet Mach Number, Exit Mach Number and Exit Gas Angle are given on Pages 11 % 24. The Airfoil coordinates are given at the very end of the document. Unfortunately the Inlet Static Pressure for the Vane 2 (IGV) is not given. Thus the ratio between total and the static pressure (stated in the ises.xxx file) is unknown.

I just assumed an isentropic coefficient kappa of ~1.3 for the Inlet Plane of the LPT in order to provide the pressure ratio using the standard isentropic eqation which relates between Mach Number, isentropic coefficient and pressure ratio.
So the calculated pressure ratio P1PTin would be ~0.91. (I know that's not the best scientific way but i had no other idea how to get the number)

Talking about the definition of the Airfoil coordinates:
The Mises manual states that the X and Y Coordinates should be in units of some arbitrary reference length Lref. It also states that if the blade chord is the reference length (unity) and the initial Reynoldsnumber REYNin is specified 1.0, then the calculated Reynoldsnumber would be the "usual chord based" Reynoldsnumber.

Therefore i divided all the Airfoil Coordinates by the chord length (given in inches)
Knowing about the reference length i was wondering whether the Pitch should then be "chord based" too, since "every" length is in reference to the chord length. Maybe one of you can answer that question? Unsure what to do, i divided the original Pitch length by the chord length in my further analysis.

Going forward i set up the blade.xxx and ises.xxx file. I´ve attached both of them so that in case anybody would like to do the same analysis you have an easy start.

The constraints i'm using are as follows:

1 - Drive Inlet slope to initial Inlet slope
2 - Drive Outlet Slope to initial Outlet slope
4 - TE Kutta Condition
15 - Drive Mach1 to initial inlet Mach number

The only initial Inlet and Outlet conditions to be defined are then the inlet & outlet Mach numbers, the inlet pressure ratio and the inlet & outlet m'-planes.

At first an inviscid solution should do, so i leave the initial REYNin = 0.

When i use 10 iterations for the ises program and no Kutta Condition for the Grid in iset the Cp distribution looks like the one in figure 1.
When i use the same amount of iterations but apply the Kutta Condition for the Grid in the iset program (without having the LE Kutta Condition defined as a global constraint) i get what you can see in figure 2. Without the Kutta Condition the exit Mach number M2 is significantly higher than with the Kutta Condition applied in which case M2 is also higher than the given M2 in the Design Report (M2=0.657).

I wonder why there are such big differences and when one should use the Kutta Condition in iset (type -999) and when not.

Also i am wondering which type of definition for Cp is valid? Usually the standard definition is not valid for compressible flow right?(the Cp=(p-p1)/0.5*roh*V²)
The Mises manuel does not give any recommondation on when to use which of the 3 types of possible definitions for Cp.

Generally i'm not sure which variables and constraints in this particular case are best fitted. If you have any comments on my "compilation" of variables and constraints, feel free to comment on that in detail. Another question: Is it possible to make a sound jugdement on the velocities in case there is no pressure ratio available(like one has only the Mach Numbers)?

What i'm ultimately after is the boundary layer edge velocity Ue. For that i believe i need to run a viscous case, thus i need clarity on the whole Chordbased Reynoldsnumber issue mentioned above. When i plot Ue vs x, do i get a dimensionless Ue and in what reference is that given?

Thank's for reading through all of this if you did it and many thank's in advance to everyone who can help me out on the issues i have with this program. As you can see i'm using it just since a few days and i try to get as much info as possible from the manual, but some things are just not super well documented and would be just very handy to be told by experienced users of the program so that i don't waste too much time on the little things.

Yours faithfully
Solareclipse

[blackjack]

In two minutes, I plot the geometry with mises/iset - see pitch.ps

Surely, the pitch you've specified is too small.

The second image shows the grid at the trailing edge.
The trailing edge pressures behave badly because the lower surface has not been truncated properly - delete the last point in the blade file.

REYNin is the Reynolds' number based on unit dimension. If chord=1., REYNin is Reynolds' number based on chord. REYNin=1. is not correct, unless the unit of length is very small, e.g. micron.

Correct the pitch and specify REYNin (chord).

[blackjack]

The attachment

[Solareclipse]

Thank´s for replying!

I missed the "bad" last point in the blade.xxx file, thanks for pointing that out! I guess it is good to always make sure that the outlet streamlines are nearly parallel.
Also maybe i interpreted the solidity in the documentation the wrong way, thus the small pitch.

I have some more questions:

1. Is there any difference whether i use imperial or SI units for Mises? Like should i use the profile coordinates in m or in inches?
2. The Chord length in cm is 7.244. If i want to choose a chord-based Reynoldsnumber REYNin, say REYNin = (V1*chord/nu1), would i have to divide all the X and Y coordinates by the chord length or would i not have to do that? This is what i don´t get. The manual says "If (X,Y) are also
defined so that the blade chord is unity, REYNin is then the usual chord-based Reynolds number.". Can´t i specify an "usual chord-based" Reynolds number REYNin without defining X and Y so that the blade chord is unity?
3. Do you think having only the angles and the inlet and outlet Mach Numbers is sufficient data for a good calculation or do i need at least one pressure ratio at the inlet condition?
4. Can you tell me about what the generated BL data in the Iplot program states? There are the columns x, y, s, b, Ue/a0. I think "s" is the arc length/the surface length of each blade surface section. It starts at the stagnation point and culminates up until the point of kutta condition. "b" i don´t know what it is "Ue" must be the boundary layer edge velocity, but what is "a0"? I can´t find a0 in the manual, it´s not documented
5. Can you tell me about when it is useful to specify the LE Kutta condition in the iset program? I believe it changes only the grid slope but not the actual stream slope in the later calculation, is that right? Like applying the LE Kutta condition does not "destroy" the original intended Inlet gas Angle.

Thank´s again for replying!

Best wishes,
Solareclipse

[afikr]

Hi

I am new to MISES. I am planning to do a inverse blade design based on a new surface pressure target.

From the user guide, I think a modal inverse design suits my case since I am starting from an arbitrary blade shape.

But I am stuck at how to set-up the modal-inverse case.

I don't quite understand how to choose the number of mode(s) and mode shape(s).

Can anyone of you please explain how varying these parameters will help me get the desired airfoil shape?


Many thanks