September 21, 2018 at 1:01 amLong YunSubscriber
I have some questions when I read the literatures about the energy spectrum.
When we calculate the turbulent flow with Large eddy simulation, it is important to make sure to resolve the scale in the inertial subrange. I want to see the Kolmogorov spectrum law (-5/3 law) in my calculation results. While, how to make the spectrum for turbulent kinetic energy ?
September 21, 2018 at 9:31 amraul.raghavSubscriberCould you provide information regarding the solver you’re working with? Is it Fluent or CFX?
September 21, 2018 at 12:12 pmLong YunSubscriber
September 21, 2018 at 5:53 pmraul.raghavSubscriber
Plotting Energy Spectrum for LES simulations in CFX:
Step 1: Achieve a statistically stable or averageable state, where turbulent instabilities due to the initial condition effects are convected out of the system. This might be a minimum of 1 through flow cycle.
Step 2: Create the following expressions for TKE.
C = 0.18 #(for Smagorinski, C = 0.18 / WALE, C = 0.5)
delta = (Volume of Finite Volumes)^(1/3)
resTKE = 0.5*((u-u.Trnavg)^2 + (v-v.Trnavg)^2 + (w-w.Trnavg)^2)
unresTKE = ((C*delta*Shear Strain Rate)^2)/0.3
totalTKE = Total TKE = resTKE + unresTKE
Create an Additional Variable > TKE > Variable Type: Unspecified; Units: [m^2 s^-2]; Tensor Type: Scalar.
Inside the domain panel: Domain > Fluid Models > Additional Variable > TKE > Option: Algebraic Equation; Add. Var. Value > totalTKE
Step 3: (In CFX-Pre) Create monitor points at a few locations in the flow field (at specific regions of interest). Monitor TKE at those points.
Step 4: (In CFX-Solver) Monitor TKE at the all points (separately). (i) Workspace > New Monitor > OK; (ii) Plot Lines > USER POINT > TKE > *Monitor Point Location* > OK; (iii) Range Settings > Plot Data By > Simulation Time.
Step 5: (In CFX-Solver) Run for sufficiently long time so that you get a sharper energy spectrum plot. Once the simulation is complete, right click on the screen to save the monitor plot as a csv file.
Step 6: (In CFD-Post) (i) Insert > Chart > OK; (ii) Data Series > File (Select the saved csv file); (iii) General > Fast Fourier Transform; (iv) X Axis > Frequency > Log Scale; (v) Y Axis > Magnitude > Log Scale; (vi) Line Display > FFT Line Type > Lines; (vii) Apply. This will give you the energy spectrum.
Hope this helps. Let us know if you have any issues.
June 6, 2019 at 7:49 pmjoemonjacobSubscriber
I am working with Ansys Fluent 17.2 and trying to get spectrum for turbulent kinetic energy. Can you please help me with the energy spectrum in Fluent.
My problem is 'flow past a circular cylinder' and I have the simulation results with 'Data sampling on'. To get turbulent kinetic energy variation along a line, do i need to monitor velocity for all points throughout or can postprocess from the available variables in LES .dat file.
- You must be logged in to reply to this topic.
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 in cfd post
© 2023 Copyright ANSYS, Inc. All rights reserved.