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propeller'performance
Hi,David
I meet some problems,
First,after BEM analysis,i find the propeller’s efficience is very low (max efficence is only 0.4,2000rpm,freestream speed 80m/s),I have tried to change the airfoil,but the result didn’t changed.
Second,I want to confirm the definition of Cp and Ct,is Cp equal to P/(ρ.n^3.D^5),is Ct equal to T/(ρ.n^2.D^4)? n=rpm/60,D is diameter of propeller.
After turbine simulation, i found the result of Cp ,Ct are too big
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Hi mozha,
the PROP BEM was validated with the NACA TR594 propeller geometry. Measurements can be found in this report:
https://ntrs.nasa.gov/api/citations/19930091669/downloads/19930091669.pdf
You can find the project file for his propeller (NACA_TR594_Propeller.qpr) in the /SampleProjects folder of the QBlade directory.
Regarding the definition of Cp and Ct in the turbine simulation module: these are defined after the standard conventions used in wind turbine aerodynamics.
BR,
David
Hi David,
Since the Cp and Ct in QBlade for “Optimize” function based on the formula of the wind turbines, as I known it is far different from the formula for the Cp and Ct for propellers, can I use this one “trick” to obtain my desired Ct or Cp in QBlade for the propeller? My intended solution is changing the input of the power or thrust value to achieve the desired Cp or Ct?
For example, my propeller’s Pshaft = 503000W so if I input this value into QBlade optimize, I would get the Cp value = 0.39, far different from my propeller’s Cp is 0.186. Now I would input another value (Pshaft=240000W) to get the Cp = 0.186. Is it meaningful or meeting any physical error? I know it sounds weird but can you suggest any further solution to solve this problem for the “optimize” function of QBlade for propellers.
Thank you for reading my questions.
I look forward to hearing from you soon.
Hello,
to design and model propellers, QBlade contains a dedicated PROP mode, see: Setting the Design Mode
When in PROP mode the blade design module contains optimization functionality for propellers.
Furthermore, when in PROP mode you can carry out steady state BEM performance calculations for your propeller design, which include the propeller specific variables, the advance ratio and propeller efficiency (η).
BR,
David
Hi David,
I have used the PROP mode already and I understand that QBlade applied the method of “Adkins_Liebeck_DesignOptimumPropellers_1994” for the “Optimize” function, however as mozha stated above, when I put my desired thrust or input power in the “Optimize” function, the CT and CP with respect to my thrust or power input is far different from what I manually calculated from the Ct and Cp formula for propeller (Ct = T/(ρ.n^2.D^4); Cp = P/(ρ.n^3.D^5)). And your answer is CT and CP in that “Optimize” function for Propellers use the formula of Ct and Cp for wind turbines. So my concern is: Is it reasonable to put different desired thrust or input power to meet the Ct or Cp in my manual calculation ((Ct = T/(ρ.n^2.D^4); Cp = P/(ρ.n^3.D^5))).
Thank you for reading my question.
Looking forward to hearing your reply soon.
Best regards,
Thinh.
Hi Thinh,
When working in PROP mode, the Cp and Ct coefficients evaluated during steady-state BEM simulations are defined specifically for propellers.
Their relationship to the corresponding wind turbine coefficients is:
Cp_prop = (π / 8) × Cp_turb × (π / λ)^3
Ct_prop = (π / 8) × Ct_turb × (π / λ)^2
where λ is the tip speed ratio and (π / λ) = J, the advance ratio.
During time domain simulations in the turbine simulation module, all performance coefficients are defined using the wind turbine convention.
To minimize confusion, I’d recommend working with the absolute values for thrust and power when running time domain simulations, and then computing the propeller-specific performance coefficients from those values if needed.
BR,
David
Hi David,
I got it, so if my desired thrust for the propeller is 2400N, in the “Optimize” box, I just need to put in the value of 2400 for the thrust and ensure that QBlade would generate the geometry for the propeller that will achieve 2400N despite that the CT shown is different from what I’ve calculated due to the CT in “Optimize” function using the CT for wind turbines.
Thank you for reading my question.
Looking forward to hearing your reply soon.
Best regards,
Thinh.
Hi Thinh,
as mentioned previously, the coefficients and are calculated for propellers only within the steady BEM analysis.
Once you’ve designed a propeller, you can evaluate its performance using the steady-state BEM module in PROP mode—this is where and are specifically calculated for propellers. Conversely, when in HAWT mode, the steady-state BEM analysis calculates and for wind turbines.
In the Turbine Simulation Module, which runs simulations in the time domain, C and are always evaluated based on the wind turbine definitions.
It’s also important to note that during propeller optimization, no value is used—these coefficients are only generated during steady-state BEM or time-domain simulations.
Best regards,
David
