I am trying find the heat transfer coefficient, by adding surface heat transfer coefficient using following parameter and have two questions

(a) i do not know why the surface heat transfer coefficient for laminar and turbulent flow in a horizontal pipe is identical, using this method.

(b) how to plot the surface heat transfer coefficient, using this method if surface in not a line.

Thank you

]]>20 particles are getting injected at each time step but my particle history is not accounting for it. Images are attached for reference.

please help.

In case of flow over a flat plate, we have laminar region, transitional region and turbulent region. If plate is long enough to go to turbulent region, we can see all three regions. Question is how to model fluid flow over plate? how to say partly laminar, partly transitional and partly turbulent .

Thank you

]]>I have already turned on the solidification and melting option. I can see the solidus option in fluid only.

]]>In this photo, they are but not in my case, it's photo from YouTube video.

We are working on a project named "Air lubrication system of the ship" and trying to find out "Skin Friction Coefficient " of the ship with or without air bubbles. Here is a sample video:

But we are facing some problems. Can you pls help us by giving any tutorial (can be paid or free) or advice so we can complete the project?

Thank You

]]>I want to have two phase (vapor and liquid) inside a 3D tank.. i.e., vapor and liquid in saturated conditions inside tank.

I created the vapor and liquid regions using adapt option in FLUENT (2020R2). However, when I am patching the volume fraction (after hybrid initialization), near the interface layer the cells will have both vapor and liquid... so when I patch the liquid region as 1 and vapor region as 1 the FLUENT gives the warning "The sum of phase volume fractions exceeds 1 in some faces(s). This can lead to potentially erroneous initialization."

Will this affect my solution, and if so, is there any option to overcome this?

Additionally, FLUENT gives error (after patching and re-initializing) "Floating point exception"

Thanks in advance

]]>We try to solve the following problem using ANSYS Fluent:

We have a flow in a tube where we want to solve the tube body using transient solver. We know the heat transfer coefficient from the literature. Our tube is comprised of phase change material, hence it has a transient thermal behavior. we try to understand how to solve the conjugated heat transfer problem in ANSYS Fluent without simulating the tube flow.

We know that in the inner tube wall there is the following boundary condition:

q = h(Tm –Tw) where Tm is the mean temperature of the fluid flows in the tube and Tw is the inner tube wall temperature, the temperatures are functions of time and coordinate x, all the other boundaries are assumed insulated.

we formulated another transport equation for the tube flow (energy balance):

ρC_p A (∂T_m)/∂t+m_dot ̇C_p (∂T_m)/∂x=h(T_m (x,t)-T_w (x,t))

This is quite basic, but we could not find how to do it. I think the approach might involve using UDS, UDM and UDF.

I would like your help with ideas how to deal with this issue.

If something is not clear, please let me know.

Thanks

]]>I am looking to model two water droplets merging together into one droplet, over a hydrophobic surface. The primary phase being air and the secondary being water.

I am achieving the merging but the physics is a little off in that the first droplet detaches then merges into the second one. When I try to move the droplets up, gravity seems to not work. they simply flow in the x direction. Wall contact angle set to 155°, wall - no slip/stationary wall, Also initializing the problem from the inlet causes a numerical instability (the droplets disperse into the domain). But when all initialized values are 0, it creates the merging I am looking for. Is this appropriate? From the EdX FEA course I believed inlet initialization was best.

Here are the current settings I am seeing some success with.

- Model: VOF, gravity on, transient
- implicit, sharp interface model, surface tension =0.072

- Viscous Model: K-Omega SST, Low-re correction on, constants: default, production limiter on
- scheme: Fractional Step
- gradient: Least square cell based
- pressure: PRESTO!
- momentum: 2nd upwind
- volume fraction: Compressive
- Turbulent kinetic energy: 2nd upwind
- specific dissipation rate: 2nd upwind
- Transient formulation: non-iterative, 2nd order implicit

Droplets created using cell registration - patched in initialization. Volume fraction of each drop = 1.

My goal is to simply have some appropriate physics before moving on to finer mesh and 3d implementation. Is the Eulerian VOF a better method to implement here?

Any and all help would be appreciated, apologies if not located under the proper category/thread.

Thanks

I'm doing a conjugate (thermal and fluid dynamic) study on a metal foam representative elemental volume (RVE) which would be placed on a fluid domain (air). The experiment consist on a heat flux placed on the bottom face (face whose normal vector has the same direction of -Z) and an air flow going forward on +X direction. The expected result is a conduction through the metal foam and convection between the foam and the air.

i'm using ANSYS academic version, that's the reason the mesh is the way it is.

i'm rather confused with the boundary conditions and, maybe, about the named selection i have to set.

I set the following named selection and boundary condition:

- "inlet": velocity inlet=0,5 m/s
- "outlet": Pressure outlet, gauge pressure=0
- "slippery walls" (the ones that limit the domain): shear stress= 0 on all the compenents, and a convection condition
- A worksheet that selects all faces at Z=0: heat flux at 100 W/m^2

the model was **Steady,** **Pressure-Based, Viscous (Realizable k-e), Energy On, **the solution method used is **Coupled.**

the simulation was planified to calculate 2000 iterations but it clearly failed so i stopped the calculations.

i hope you can help me with this or advice me. I'm this close ->...<- to end these study and getting my mechanical engineering degree!

Regards!

Nicolás Parodi Saldivia

]]>

I am not an expert in writing UDFs and have started just a few months back. From what I understand, I can get the index of the interfacial cells using F_C0 and F_C1 and update these using DEFINE_ADJUST.

Can someone please give some hints on the correct way of doing this? Any help is much appreciated. Thanks in advance.

Figure depicts the heat transfer rate with time under frosting condition. the amount of heat transfer rate increases with time at the initial stage of operation of the heat exchanger, has a maximum value at a certain time, and then decreases again. **what is the reason behind**?

I have 4 pipes coming from sea (source tank) and these 4 pipes are taking water from sea with help of water pump(p1, p2, p3, p4) and put it to tank, which is in vertical height of say 6 meter from sea. I want know

Effective combined pump flow rate for this combination of piping system & parallel pump

Also flow rate at tank individually by pipes also

I was looking at the transport equations for multiphase flow (Equations 14-387 and 14-388 in Section 14.5.18.1.3.1, 2021 R2 Fluent theory guide) and I cannot understand why, in the 4th and 5th terms of the right end side, the turbulent viscosity is divided by what I believe is the surface tension.

"*σ" *appears but the text does not say what it is, however it was used to refer to the surface tension or turbulent Prandtl number in this chapter.

The problem is that, dimensionwise, the equations only make sense if "*σ" * has a dimension of a density [M]/[V]^3.

I do not know if this sigma refers to some parameters that I have never heard of before, but has a dimension of a density, or if this "*σ" *should be a "*ρ*"*, *the density of one of the phase.

Thank you for your answers,

Regards,

KF

]]>Firstly, I work on NACA 2242 profile. (Re = 1*10^6, chord length = 1m, v = 14.607 m/s). I use c-type(10c-10c) domain and structural mesh(figure 1).

I use k-omega SST model. Whatever I do I couldn't find correct drag coefficient. ( There is no problem with residuals(Figure 2). Even I try it with y+ = 1 , I find same result.)

I find Cl = 0.1936 and Cd = 0.013204(figure3) ,but Cl = 0.2442 and Cd = 0.00568 (http://airfoiltools.com/polar/details?polar=xf-naca2412-il-1000000) at Re = 1*10^6. Do you know what is the problem.

Thanks for responses...

I have a question regarding the integration of a ML model in ANSYS Fluent.

Is it possible to combine high-fidelity solutions in local regions and ML methods in coarse regions?

If yes do you have any documentation to recommend ? Or do you have an idea for how to proceed ?

Thanks in advance!

]]>Can someone help me with why this is happening and is there something I'm doing wrong.

The above image is of a file with HPPC data which I use for parameter estimation.

]]>What exactly will be the required input for such simulations. Probably I will have to define the expression of this condition.

Any leads on how to proceed with such calculations will be helpful.

Thanks.

]]>when defining injection for DPM calculation and activating the Discrete random walk model a time scale constant will be required

i noticed that increasing this number will increase the erosion rate and this may be explained by that the particles will have more time in the domain so more compacts and hence more erosion(at least my understanding)

in Fluent theory guide it was mentioned that for K-e models a value of 0.15 is recommended while a value of 0.3 is recommended for RMS model

i want to know what is the basis of this values and during real simulation how can we choose best value for our model or geometry

is this constant geometry dependent if so how can we estimate it

if any has a good reference to read besides the fluent manual please share with me

Regards

]]>I want to simulate the inlet plenum with quiescent air and believe a total pressure inlet boundary condition is the correct choice; however, I am uncertain if I should specify total pressure as constant 0 Pa(g) or -gravity*density*y. Both options give something similar to the shown vector plot that has the bulk of the streamlines hitting the pile originating from the top of the hemisphere.

My expectation is that the stream function in the plenum should be characteristic of a line sink (psi = m*theta) and therefore am suspicious of the inlet boundary condition definition. Thoughts?

I have a question about large eddy simulation (LES) when using one of the available models in Fluent for shear-dependent viscosity, μ_a. Is the software solving the following grid-filtered (~) momentum equation?

or is it solving this other form?

Thank you in advance.

Best regards,

Arturo.

]]>These were my results of mesh quality, what does target skewness mean?

Would my quality be poor? how could i fix it?

I have two boundary conditions. One velocity inlet with a continous phase a velocity boundary, which is pulsating. So it's something like a sinus-function. And a dispersed phase, where the velocity it's negative, so dispersed phase can go out of the inlet. Is a volume fraction=0 a good asumption or will it lead to only entering continous phase and mass flow of dispersed phase is zero. Should I then use an assumption for volfrac (something like volfrac=holdup of column). Or also a pulsating volfrac.

The outlet is a pressure outlet, where the backflow volfrac is one. The inlet is at the top of the column and the pressure outlet at the bottom.

So it's a countercurrent pulsating flow. It's for simulation of a liquid-liquid pulsed (and stirred) extraction column. The continous phase is the heavy phase and the dispersed phase is the light phase.

Gravity is considered in the model, so also the bouyancy, right?

Thank you

]]>Below is the contour image of my setup. The left wall is at subcool temp and the interface will move towards the right as the condensation occurs. I want to plot the thickness of the condensed region as it moves towards the right wall.

Dose = Σ E * **Δt**

I know that I need to write a UDF for this process.

The problem is the radiation field would not be modeled by the Fluent, and we have experimentally measured the incident radiation at several points in the room. However, I don't know how the data should be integrated into the CFD model calculated by Fluent. Maybe a radiation field should be defined by interpolation of the experimental data.

But how?

And how should I import the radiation field data into Fluent?

]]>I need to simulate an arteriovenous malformation (attached image) any idea how to mesh? (is only blood).

Thanks for reading

I am following the tutorial *3D Bifurcating Artery*, and to create the material blood, which is non-newtonian, the Carreau model is used to model the viscosity. However, **I do not have that option**.

I am using ANSYS R2 2020 Student version.

I **do not want** to write the Carreau model **as an expression**, but

Thanks in advance.

]]>The highlighted part is the Marangoni force term. I understand that the 1st term(the surface tension force term) is modeled as CSF by FLUENT and added by the VOF model itself. I have written the UDF for the 3rd term which is the recoil pressure term.

First I read that FLUENT can add the Marangoni force term arising out of variation in the surface tension due to temperature. This is mentioned in this image.

But then I read in detail in the theory guide and found out that the CSF term is only for a constant surface tension and for the tangential Marangoni force term(arising out due to variation of surface tension), I have to add it myself. What if I have a temperature dependent surface tension coefficient? Both the statements are completely opposite. Can someone clarify please?? I am using Ansys 2020R2

I'm trying to create a UDF which analyses the shear stress gradients (and hence contribution to the X and Y momentum) for steady, compressible turbulent (SA) flow.

This can be done easily by rearranging the navier stokes such that the X term would look like

Grad(P)[0]+ rho(q . nabla)q [0]

where q is velocity. We have all these properties which can be easy to implement in a UDF and visualised using a user defined scalar.

However, I want to do this using the shear stress alone where we have tau xx[0] + tau xy[1] for the X momentum term which should then be equal or close to equal to the other method. However, I have been unsuccessful in doing so, my stress components are given as follows (note some over expansion etc for data analysis purposes). Instead of this longwinded way is there a shear stress variable available or do I need to calculate this. Is there a clear problem with my implementation process?

/*tau_xx*/

C_UDSI(c,t,0) = (-2/3)*(C_MU_L(c,t))*(C_DUDX(c,t) + C_DVDY(c,t)) + 2*(C_MU_L(c,t) + C_MU_T(c,t))*C_DUDX(c,t);

/*tau_xy*/

C_UDSI(c,t,1) = (C_MU_L(c,t) + C_MU_T(c,t))*(C_DVDX(c,t) + C_DUDY(c,t));

/*tau_yy*/

C_UDSI(c,t,2) = (-2/3)*(C_MU_L(c,t))*(C_DUDX(c,t) + C_DVDY(c,t)) + 2*(C_MU_L(c,t) + C_MU_T(c,t))*C_DVDY(c,t);

Thanks.

]]>Thansk a lot.

]]>sqrt(ND_SUM(ND_DOT(C_DUDX(c,t), C_DUDY(c,t), C_DUDZ(c,t),(C_DUDX(c,t) + C_DUDX(c,t)),(C_DUDY(c,t) + C_DVDX(c,t)),(C_DUDZ(c,t) + C_DWDX(c,t))),ND_DOT(C_DVDX(c,t), C_DVDY(c,t), C_DVDZ(c,t),(C_DVDX(c,t) + C_DUDY(c,t)),(C_DVDY(c,t) + C_DVDY(c,t)),(C_DVDZ(c,t) + C_DWDY(c,t))),ND_DOT(C_DWDX(c,t), C_DWDY(c,t), C_DWDZ(c,t), (C_DWDX(c,t) + C_DUDZ(c,t)),(C_DWDY(c,t) + C_DVDZ(c,t)),(C_DWDZ(c,t) + C_DWDZ(c,t))))

+ (rp_axi ? (2.*SQR(C_V(c,t)/C_AVE_Y(c,t)) + (sg_swirl ? (SQR(C_AVE_Y(c,t))*NV_MAG2( C_STORAGE_R_NV(c,t,SV_OMEGA_G))): 0.)): 0.))

I understand the first part of the definition which is basically the second invariant of the strain rate tensor. But for axisymmetric case part(rp_axi part) I don't get how those terms appear. Can anyone explain/refer to any theory resource to learn how those terms appear for axisymmetric case? Also, I can't find definition of the terms too in the manual.

]]>Now, as I understand FLUENT does not create a sharp interface between 2 phases and the volume fraction change takes place over a number of cells. So, I cannot exactly use 0.5 as volume fraction to apply the source terms. I am taking a range of volume fraction for the applying the source terms(0.05<C_VOF<1). Next I understand that I should also use the cell centre z coordinates to identify these cells which have a volume fraction in that range? So, how to know the number of cells at the interface?