BEMT propeller design software


#1

Hi friends:

Im just finishing a Propeller design and analisys software that could be of your interest, and could be my modest contribution to this project.

It works by the very well known Blade Element and Momentum Theory, taking into account the Prandtl model for tip loss calculation.

Calculations take into account enviromental variables such as temperature and depth, as well as, fluid properties.

Compared with a CFD, its results are good enough.

Anyway, it would be worth for nothing without a lot more use, testing and comparison of results.

As the simplified BETM starts from the "small angle" and hence, constant Cl slope hypothesis, which in our case, are not really valid assumptions, this software reads Hydro/Aero-dynamic coefficients from a Polar Curves file.

Its now full functional, and only the "Manual" input of Prop and Profile datas is still on course.

The software has been designed for reading those datas from standard .CSV files, that manuel part is only an add, not needed for making it work.

Soft output are:

Thrust & Torque vs RPM

Thrust and Torque vs SPEED (Advance velocity)

Propeller efficiency vs RPM or SPEED

Thrust and Torque coefficients vs J

Cavitation number vs logarithm (critical pressure coefficient)

Radial pressure distribution (Blade stress)

Cavitation analisys

All above graphic and in tables.

EDITION capabilities:

The whole propeller geometry can be changed inside the program.

Tables can be directly cut and pasted on Excel.

If it could be of any interest for this project, I'd have no inconvenience publishing it for free.

My sincere congratulations for this nice and interesting project.

Best wishes and regards

- Ion -


#2

Hi again:

May be my explanation above did not look very usefull.

Let me post some pics with the results for a K7063/5 propeller. (Kort-Diam 70mm-Pitch 63mm-5 blades)

The goal is finding better thrust and less torque conditions, with the best Propeller performance for the required RPM.

Final approach involves avoiding cavitation.

For an underwater vehicle, cavitation may happen but vanishes as depth increases. Hence working conditions are to be taken into account.

Loading file/Checking propeller geometry data.


First approach: Fix required speed and look for better RPM.


Check propeller efficiency at those conditions.


Fix RPM and "scan" results for a range of speeds. Will return an idea about the arrangement flexibility.

and a better approach to the best working conditions.



Now: By reading at output tables, the Propeller results under the given conditions can be read.


Last step:Blade checking for Cavitation, mechanical stress ......

Blade editing and refining .....


Almost in all cases, props are commercial. Hence geometry changes cannot be performed.

But, if not for self building a prop, editing can lead to choose the commercial one which better fits the requirements.

Would like to get some opinions and feed-back.

Regards

-Ion -


#3

Software bug corrected.

Solution values corrected.


#4

it is possible export 3D geometry?

I am interested to have a copy for test


#5

Hi Marzio:

The software above has been modified and corrected. For some conditions it returned odd results that have been solved.

About exporting .....

Not by now. Profile properties are read from a polar table and not directly calculated, hence only layout and pitch geometry datas are required by the program.

Now at work: Including Panels Method for direct pressure-speed fields calculation.

NOTE:

The ROV propellers are very similar to those of the KAO or Gawn-Burril 3 bladed series.

I have an Excel file by myself that can compute, choose and export (3D coordinates csv file) for the best propeller (GAWN and WAGENINGEN) into given working conditions.

It would only be required to make a correction for the wake factors, that in my File is computed for surface units, and for scale, as mine is developed for real ships.

In both cases, if you use them, please dont forget to credit the author :-)

Regards


#6

Can you please share this software?


#7

Hi Pranesh:

It's still under work and is not fully reliable. I use my spare time for developing that software so it goes "easy easy".

As you may know, the BEMT-POTENTIAL FLOW models combination, allows for a first approach to propellers performance, Its quite a good tool for propeller design.

But for already built or comercial propellers, the way to go is working from Testing Channel datas.

Anyway, if you are interested in any propeller calculation/optimization/performance curves, just ask. I can perform almost any calculation and share results.

Regards


#8

We would like to design a propeller of diameter 200mm, 3 blades, Thrust required=250N. forward speed=3knots

What are all the other inputs required?

Can you please send me the blade geometry?

Can you please send me the sample calculations?


#9

OK Pranesh:

I can start with those data.

Do you plan to use a ducted or an open propeller ?

A key thing is knowing the "wake factor" of the "hull". This factor gives an idea of the interference of the hull in the flow that arrives to the propeller disk.

I can get a good approach for the Wf from a general description.

May you give me a brief description of the "sub/boat" hull shape and its general dimensions. Is it torpedo like, box like .... ? ........ ?

Of course, I can give you a general view of the calculations procedure.

Regards


#10

Hi Pranesh:

Some points regarding your Propeller request.

Any calculation results on a requirement of around 12000 Watts, for moving such a propeller at, around again, 1800 RPM.

Working RPM can be changed by modifying the propeller design.

Best preliminary approach is:

D=200mm; P/D= 0.64; AeAo=0.5: Blades=4: Raked and Skewed.

Thrust=278 N; Torque= 56 Nm; At 1800 RPM

Efficiency: 0.507; Cavitation number: -0.74 (Not cavitating)

May I know your power and/or RPM limitations/requirements ?


#11

It is for ROV of size 1m x 0.7m x 0.8m


#12

I guess 12000 watts is very very high. May be around 1200 Watts.

Speed is OK.


#13

You're right Pranesh. I messed units up.

I'll follow a logic proccess. Results are not accurate becouse many assumptions are made, but is one way for a first approach.

Diameter: D=0.2m; Dragg, T= 250N

Velocity V=1.54 m/s

Assumptions are based on statistical models and experience.

Assumed efficiency= 0.4:

Assumed coefficients Kt and Kq: Kq=0.02: Kt=10Kq

From:

eff= J Kt/(2 PI Kq) and Kt=10Kq

J= 2PI eff/10: J= 0.25

With J= Va/(N D); N= Va/(J D).

V=1.54 m/s

N= 30.6: RPM= N*60= 1838

W= 2*pi*N= 192.5 rads/sec

Kt= T/(dens NĀ² D^4): Kt= 0.1664: Kq= 0.01664

Torque: Q= Kq dens N^2 D^5= 5 Nm

Power required: P= Q * W = 962.5 Watts.

Well:All above is a very rough approach, but gives a first sight of the required propeller.

Now: Accurate calculation, too long for being explained here, returns:

Propeller type: Kapplan. Duct 19A

D=0.2m: P= 0.144m: P/D= 0.72

Expanded area ratio: AeAo=0.5.

Blades: 4

RPM: 1580

Delivered Thrust: 255 N

Required Torque: 5 Nm

Required Power: 704.88 Watts

Efficiency: 0.558

Kt= 0.23: Kq= 0.019

Cavitation number: -0.79 (NOT CAVITATING)

For a more accurate propeller fitting, a few more things are required:

Hull wake factor and wake field (Depends on shape)

Propulsive efficiency (Shaft, bearings, gears ... power "waste")

Appendages location: Fins, rudders ......

I can attach the geometry file here.

May I know how are you going to build it ? Material ?

Regards


#14

Here you have some graphs:

Solutions for best RPM run between 1580 and 1610. Quite a good approach.



#15

Good to see the graphs...Congratulations Ion..

Can you please share the software and procedure for making the calculations....


#16

Material is going to be SS431(for blade) and SS303 for the hub


#17

Can you please give me some reference material for understanding the entire design?

Pranesh


#18

Very interesting, what the system requirements for your program, such as, Windows, Linux etc...

Good work by the way


#19

Hi all:

Thanks a lot for your appreciation Chris.

The software is built from a number of VBA macros for Excel that link with another group, built for Solidworks.

We found it a lot more useful than making the whole program from scratch. Interpolation procedures, matrix algebra .... etc, are already implemented on Excel making the way a lot simpler.

The link between Solidworks and Excel allows for choosing the propeller from the Calculations module and directly building a 3D accurate model in Solidworks.

Hence, it runs on Windows by now.

Hi Pranesh: The software we use, not intended for general users, is only useful if the user has a good theoretical background, as required input data are a little bit cryptic for a novice.

About some reference material .........

Subjects:

General hydrodynamics.

Blade Elements and Momentum Theory(BEMT)

Potential Flow theory/Circulation theory (Vortex Lattice methods)

Experience channels statistical propeller series.

May be with a good understanding of the three subjects above, a good understanding of the Propeller design procedure can be got.

All above requires vectorial calculus.

As it always happens with engineering, the procedure can be learnt as a parrot, only following a set of instructions. The problem comes with interpreting the results and understanding the requirements.

You can easily design a propeller by only using the Polinomials for sistematic Propeller series. Starting from Diameter, Pitch to Diameter ratio (P/D), Expanded to disk area ratio(AeAo), and Velocity of advance to Diameter and RPM ratio (J-> Coefficient of advance) Those sistematic series return Kt and Kq (Thrust and Torque coefficients)

The key is making the correct choices for the suitable series and the propeller specifications ranges related to the propulsive requirements.

A good lecture for starting, may be:

Marine Propellers and propulsion by John Carlton . This book gives an approach to all subjects mentioned above, but does not enter into the details.

Another good starting point, is:

Principles of Naval Architecture. Vol II

There is not a single book or work where everything related to propellers could be found. By the way, almost everyday, new things are published.

Building:

Propeller blades are not planar surfaces. I mean they cannot be built by simply bending a metal sheet.

Normal procedure is casting, and standard materials are copper alloys (Naval bronze), usually with manganese or Naval aluminum.

Anyway. Do you need 2D drawings of the propeller ? Or only a 3D file is enough ? If 3D, which format ?

NOTE: Take care with calculated thrust/power. Calculations are done for "ideal" conditions, as no information regarding the wake field, or the ship/sub design has been provided.

Some example outputs for a WageningenB4 series propeller parametric study.

Parameters: RPM and Expanded Area Ratio.

Efficiency vs Advance coeffient.


Thrust vs RPM and AeAo


Cavitation number. Same parameters.


Regards.


#20

You have done a great job....

3d file in soldworks format or IGES or OK