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Impact of a jet on flat plate and the local nusselt number

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Old   August 25, 2018, 18:36
Default Impact of a jet on flat plate and the local nusselt number
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hello,



I study the impact of a jet on a flat plate, as shown in Figure 1. The flat plate is maintained at a constant temperature of 393.16K and the air jet is 293.16K at the injection.


---


Re=200k,

U inlet= 152m /s and U outlet= 9.5m/s

P inlet, outlet= P atm

openFOAM 4.x
Turbulence model: realizableK 30<y+<300
buoyantsimplefoam
Thermodynamic package:

Code:
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState incompressiblePerfectGas;
    specie          specie;
    energy          sensibleEnthalpy;
----





I subsequently calculated the local nusselt according to the position of the heated plate, we observe the curve of Figure 2.





However, the curves from the experimental data give rather this kind of curve figure 3.










Does anyone have an idea?
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Old   August 28, 2018, 04:59
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Maybe the figures could be included, at least I could not see any figures or links to them.
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Old   August 30, 2018, 05:50
Default Secondary vortices at high Reynolds numbers
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Is it a round Jet?

I understand that you use Re=200000 in your simulation compared to Re=11000 in the experiment. You can find very good experimental data in "STAGNATION REGION HEAT TRANSFER OF A TURBULENT AXISYMMETRIC JET IMPINGEMENT" by Lee and Lee (1999). There you see that with higher Reynolds number a second peak emerges and you get a valley in the centre (yours is quite strong).
So basically both the experiment and the simulation could be correct.

The second peaks comes from a secondary vortex, for a detailed explanation have a look at
"Vortical structures and heat transfer in a round impinging jet" by Had×iabdić and Hanjalić (2008). It is amazing that a realizable-KEpsilon model can give you this secondary vortex structure.
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Old   September 4, 2018, 16:53
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You are right, they are not the same Reynolds.
But also in Re=11k, i have the same peak in the curve.

Its not about the fvschemes ? I will read those documents and i will coming back.
Thanks a lot.
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Old   September 24, 2018, 04:38
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I moved the thread because it is not related to the subject of the subforum Verification & Validiation (please read the sticked thread)
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Old   September 24, 2018, 04:49
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In the center of your jet you have a stagnation point. In this point it is not possible to move away heat. This is the result you got from your simulation.

In a reality (at higher Re number ) the position of the stagnation point moves around. This lead to an overall heat transfer, but with a less steep peek.
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Old   September 24, 2018, 04:56
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By the way, the wallHeatFlux does not represent the Nusselt number. You compare something with anything. For a scientific investigation, calculate the Nusselt number and plot it against the measurement results.
Furthermore, what do you mean with U_outlet = x m/s? It seems that you make some mistakes in your set-up too or at least you do not provide enough information for your study/analysis.
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