Prem Naik asked 10 months ago
Hello,
I have conducted a plane analysis using uniform-density triangular panels. However, I am encountering an issue where the Cl/Cd values are decreasing with decreasing the length of the fuselage with the same wing. What would be the reason behind this decreasing Cl/Cd? For your assistance, I have attached the results to this question.
Thank you kindly for your assistance.
https://drive.google.com/file/d/1doVKLxBh5Bk_Z89j9ryPBrAlx87tsKFL/view?usp=sharing
Hello,
The fuselage does not produce lift by itselft, but it could modify the drag depending on its length if you have included fuselage friction drag in the analysis. It could also influence the lift indirectly by modifying the flow around the wings.
Hello,
From the picture attached in the google drive link, it can be seen that wetted area is reducing with decreasing the length of fuselage, so overall C_D should also be decreasing, however overall C_D is increasing. What could be the possible reason for this?
https://drive.google.com/file/d/1doVKLxBh5Bk_Z89j9ryPBrAlx87tsKFL/view?usp=sharing
Thank you for the help.
Not sure why you expect that Cd will decrease as the wetted area decreases.
For instance reducing the length of the fuselage also decreases the Reynolds number and may increase the friction coeffiient.
Hello,
Thank you for responding to the questions.
I have done a CFD analysis in Ansys Fluent for a test case (fuselage + wing) to understand the difference in Lift and Drag coefficient values between CFD and FLOW5 results. Please see the attached image in the link below.
On comparison, C_D from FLOW5 is around 90% higher than CFD result. My query is whether this over prediction of drag coefficient is usually common in FLOW5 or is there anything that I could be missing out in the FLOW5 analysis.
https://drive.google.com/file/d/1IoO-BB31zTwi18f5gssLV3yOzuylrQ-A/view?usp=sharing
Thank you for the assistance.
Unfortunately I don’t have any explanation to offer. I don’t know about fluent so I can’t tell.
Fuselage drag is difficult to estimate and the formula implemented in flow5 are coarse evaluations only. They didn’t look too bad in the case of the jibe2 which you will find in the online documentation, but other than that I have very little to go on.