May 4, 2023 at 10:21 amAli BacharSubscriber
Hi All, I am currently modelling what happens, to lift induced drag, when you apply washout to a wing (Twist). However I have a few issues
1) the drag values I calculate are into the 1000s
2) the drag values oscilate between, mesh studies (I could have +ve 10000s then -ve0.001 then +ve 100s)
3) My residules never truly converge but rather oscilate at 1e-02
and i dont know why. here is the journal file for the case. I am using Kw-SST, the X/Y velocity components are set as such that there is a total of 113m/s at a pitch attitude of 0.7degrees
; READING MESH FILE
; Read mesh file (change the name according to your case)
; ENERGY MODEL
; Enable energy model and viscous heating
/define/models/energy y n n n y
; TURBULENCE MODEL
; Enable kw-SST turbulence model
; MATERIALS PROPERTIES
; Define air properties
/define/materials/change-create/air/air y incompressible-ideal-gas n n n n n n
; CELL ZONE CONDITIONS
; Set operating pressure to 86884 Pa
/define/operating-conditions/operating-pressure 86884.9682 q q
; BOUNDARY CONDITIONS
; Set temperature to 275.65K for pressure outlets
/define/boundary-conditions/set/pressure-outlet/farfield outlet () t0 n 275.65 q q q
; Set the temperature to 275.65K, the velocity to 113 m/s and the corresponding angles of attack in the velocity inlet
; WARNING: be careful to the axis of the model mesh and change the velocity components (x,y,z) accordingly
/define/boundary-conditions/velocity-inlet/inlet y y n 113.17 n 0 y n 0.99993 n 0.01220 n 0 n 275.65 n n y 5 10
; Remove the residuals plot
/solve/monitors/residual/plot n q
; Set convergence criteria to 1e-03
/solve/monitors/residual/convergence-criteria 1e-03 1e-03 1e-03 1e-03 1e-03 1e-03 1e-03
this is what the mesh looks like, its got a far field size of 15metres in each direction and 30metres behind the wing, I'd argue that it is refined in all the right places (BOI around wing more refined than farfield)?
this is what the residuals look like
500 simulations doesn't seem alot but comparing with my peers is should be more than enough to reach convergence so I am not sure if going 1000+ would actually converge or just repeat the oscilation.
to calculate induced drag I create a trefftz plane at 6m beyond the aerofoil (2x Root Chord) I then used the surface integral of my custom function of: 0.5 * density * ((Vz * Vz) + ( cos (0.7) * (Vy * Vy)) - ( sin (0.7) * (Vx * Vx))) (Where x is the direction from leading-trailing edge, z is direction from root-tip and y is vertical).i then take this value divide by the dynamic pressure 0.5 * Air Density * Air Speed^2 and then divide that by the area of the trefftz plane which is 900m (30x30)
which is how i get to = 1396.322876 as its = 9858187800/7844.562451/900 which as incredibly huge value.
Anyone able to shed some help as to where I'm going wrong .
May 4, 2023 at 12:23 pmRobAnsys Employee
Convergence is awful, so I'd start there. Also check the domain size: you won't be the first person to have a 9km long wing! Then look at the NACA tutorials in the Help system to confirm the reference values are correct.
May 4, 2023 at 12:31 pm
May 4, 2023 at 1:31 pmRobAnsys Employee
Those are the numbers in the geometry tool. Check domain scale in Fluent.
May 4, 2023 at 1:36 pm
May 4, 2023 at 1:55 pmRobAnsys Employee
OK, so now check mesh quality and fluid properties. There's a reason for poor convergence, it's just a process of working through the model to figure out what the cause is, then fixing it.
- You must be logged in to reply to this topic.
Boost Ansys Fluent Simulations with AWS
Computational Fluid Dynamics (CFD) helps engineers design products in which the flow of fluid components is a significant challenge. These different use cases often require large complex models to solve on a traditional workstation. Click here to join this event to learn how to leverage Ansys Fluids on the cloud, thanks to Ansys Gateway powered by AWS.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
- Suppress Fluent to open with GUI while performing in journal file
- Floating point exception in Fluent
- What are the differences between CFX and Fluent?
- Heat transfer coefficient
- Getting graph and tabular data from result in workbench mechanical
- The solver failed with a non-zero exit code of : 2
- Difference between K-epsilon and K-omega Turbulence Model
- Time Step Size and Courant Number
- Mesh Interfaces in ANSYS FLUENT
- error: Received signal SIGSEGV
© 2023 Copyright ANSYS, Inc. All rights reserved.