Fluids

Fluids

LIFT COEFFICIENT CYCLE

    • qamar
      Subscriber

      Hi, I am doing oscillating airfoil and I want to plot lift and drag cycles for upstroke and downstroke. I saved report definitions for lift and drag coefficients in fluent and obtained following attached text files. The files have 3 columns as '"Time Step" "report-def" "flow-time". I want to know how can I plot lift and drag cycles in pitching airfoil. An example from the literature is also attached.

    • Karthik R
      Administrator
      Hello,nTo generate a plot similar to the above screenshots, you will need to plot the final convergence Lift coefficient with the angle of attack. If your angle of attack is changing in your simulation, you will need to obtain this data through out the simulation. Once you have this data as well as your lift coefficient data (as a function of the same flow-time), you should be able to plot this data.nThanks.nKarthikn
    • qamar
      Subscriber
      Hi Karthik, Thank you for your reply. I have attached the lift coefficients and drag coefficients obtained through fluent force definitions, Do I need some other lift coefficient? nThe airfoil is pitching and the angle of attack changes with the flow time, how can I track the CL and CD with this changing alpha. nSecondly, the equation for pitching i am using is ?(?) = ????? + ?????????? sin(??), in which ?(?) changes with the flow time. Therefore, for example, if my alpha is 20 degree and if my time step size is 0.0003 in 10000 steps, I get the flow analysis for 3 seconds. I got the airfoil pitching upto 20 degrees and I also got the report definitions for lift and drag in fluent and I obtained the above attached .txt files showing Time Step, report-def, and flow-time nMy question is; Now how can I plot CL vs alpha from that information. Do I need some other information? Kindly guide me step wise so that I can obtain this information from the fluent.nnThank you very much.n
    • qamar
      Subscriber
      Also, is there any video tutorial available showing the procedure of obtaining such plots for unsteady flow. Thank you.n
    • Karthik R
      Administrator
      Hi,nDo you know the values of alpha_mean and alpha_amplitude as a function of time? If you know this value, you should be able to plot alpha (t) with your Flow Time. Once you have this data as well as your CL (t), you should be able to extract this data and plot them on Excel. Or is this what you are looking to extract from Fluent during your simulation?nThank you.nKarthikn
    • qamar
      Subscriber
      Hi Kremella, YES, I know alpha as a function of time step. then fluent also provides me cl wrt time step. I am hereby attaching both files. I am getting good lift coefficients, So do you think this is good as you can have a look at these files. Thank you.nn
    • Karthik R
      Administrator
      Hello, nAs Ansys employees, we are not able to download files from the forum. Please take these results into a spreadsheet and plot Cl (or Cd) vs. alpha. Do you obtain the same plot as that shown in literature?nThanks.nKarthikn
    • qamar
      Subscriber
      Hi Kremella, nThank you for your message. Yes, I plotted the results and it is not coming as in the literature. How can I show you the data. For example, the lift coefficients I am getting from fluent are as: LIFT COEFF vs FLOW TIME. I am also getting negative CL with increasing flow time. I obtained alpha but it is not completing a lift cycle as expected. nn
    • qamar
      Subscriber
      n
    • Rob
      Ansys Employee
      Remember that the forces have a vector component, as you rotate the domain the vector is constant. Coefficient also depends on the reference values, so you may find you need to do some additional calculations to extract the data you want from Fluent. n
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