The Aerodynamic calculation results displayed in VSPAERO results manager revealed discontinuity of graph curve: lift coefficients Cl vs. wing span coordinate Y in vicinity of transition zone between flaps/ailerons and wing.

[T T]

Good morning everyone,

i am especially interested in applying of aircraft wing’s pressure distribution estimated in VSPAERO and transform the pressure distribution into discrete Finite Element Modell - Nastran solver.   

I built simple wing model in OpenVsp program and run the aerodynamic analysis:   

The Aerodynamic calculation results displayed in VSPAERO results manager revealed discontinuity of graph curve: lift coefficients Cl vs. wing span coordinate Y in vicinity of transition zone between flaps/ailerons and wing. 

Fig.1 discontinuity of Cl vs Span.jpg - see attached

The Calculation of Total Lift Force Lz in calculation spreadsheet according to Cl coefficients stored in file: wing-with-controls.lod showed important change of wing’s Total Lift Force Lz.   

There is possible to avoid: - above mentioned huge discontinuity in Cl distribution along wing span coordinate Y between wing and controls components (huge difference of Cp distribution on wing between wing and controls components)?

VSPAERO Viewer results for Pressure coefficient Cp distribution:

Fig.2 difference of of Cp-1.jpg - see attached

Pressure coefficient Cp distribution - Wing  

Fig.3 difference of of Cp-2.jpg - see attached

Pressure coefficient Cp distribution – LHS Flap region enlargement  

Fig.4 difference of of Cp-3.jpg - see attached

Pressure coefficient Cp distribution – LHS Aileron region enlargement

Best regards

[Rob McDonald]

These discontinuities are not really part of the fundamental solution, but are instead an artifact of the process of integrating the loads into the spanwise load.  The routine that does this searches for the local chord by starting at the TE and searching forward for the LE -- for control surfaces it can get a bit confused  and you end up with issues in where the load gets accounted (cl*c) vs. the found chord.  Plot the chord distribution and you'll see that it has a corresponding jump.

I'm optimistic that this will improve down the road.  Using the load (rather than cl) will probably work a bit better.

Rob

[T T]

Good morning everyone,

a lot of thanks for Mr. Rob McDonald for the above answer.

The main objective of my use of VSPAERO software is to generate the most accurate distribution of pressure coefficients Cp on aircraft and to transfer estimated coefficients Cp into the Nastran input file.

I built simple wing model in OpenVsp program and run the aerodynamic analysis (I attached to my email file for VSPAERO: wing-flaps-ailerons.vsp3):   

a.

The geometry modell of wing was defined in Length units [mm]. 

b. 

The aerodynamic analysis was performed for: 

  - Incidence of the wing 3.5 [deg], - AoA 8 [deg], - Flap deflection 25 [deg], 

  - Aileron deflection 0 [deg], 

  - V=24500[mm/s] (24.5m/s) with corresponding Reynolds Number Re = 2171628.312 (The Air kinematic viscosity 14.61 mm^2/s (1.461E-05 m^2/s), 

  -Altitude H = 0 [m] with corresponding Air density 1.225E-09 kg/mm^3 (1.225 kg/m^3), 

c. 

The mass properties of wing: 

  - Total mass of wing was 500 [kg], 

  - Center of Gravity shifted dX = 350.625 [mm] from X=0 mm of global coordinate frame, 

The Aerodynamic modell was prepared to analysis (with use of panel method) by applying VSPAERO settings:

More detailed Results of aerodynamic analysis:

Pressure coefficient Cp distribution  (scalled from -2 to -41) - Wing

Estimated Lift coefficients Cl stored in .lod file were affected by the Pressure coefficient Cp distribution in the region between wing and controls components.

Remark:

The other coefficients like Cd, Cs, Clo, Cdo ... were affected also.

According to .lod file it can be noted that user is able to manually change the affected coefficients to obtain more accurate aerodynamic results.

 Question Q1:

There is the way to correct pressure coefficients Cp manually or by VSPAERO software proper settings?

 Question Q2:

There is the way to better modell of Control surfaces (Flaps/Ailerons) to estimate more accurate presuure coefficients Cp distribution (I am especially interested in panel method use)?

- perhaps VSPAERO software proper settings will be the part of the solution?

Question Q3:

I prepared the geometry modell of wing in Length units [mm].

There in .lod file was not written density of air but instead 0.000 value of density was written.

There are VSPAERO settings responsible to proper input of air density in .lod file? 

Best regards

[Rob McDonald]

The air density is used as specified, but your units made it of magnitude 1e-9 -- which does not display in that output which forces fixed precision with 7 decimals of output.  You can ignore this.



Rob