I'm about to study the effect of wall roughness on particle deposition and I AM SO CONFUSED!!

Is the roughness height the same as the absolute roughness?*

any explanation?

regards.

]]>Inner Diametre is 39.60 mm, Outer Diamtre 40.20 mm and the shell thickness 0.30mm. The weight of a ball is 2.70 g.

How do I add the air into the project? I read about treating air as an enclosure in earlier versions of Ansys CFD but I don't know how to add the air flow for my project in Ansys 2020 R2.

I would appreciate if anyone can show me step by step how to achieve the above.

Sincerely,

Xiu (practice_ping_pong)

]]>I have read in many papers that in a thin thermal boundary we have high local heat transfer coefficient, i.e better heat transfer by convection. what is the reason behind this?

Thank you in advance

]]>The horsepower should be around 1. I can't figure out what I'm doing wrong to get 300 HP. If anyone has any pointers, I'd appreciate it.

]]>The conservation of energy for this model is as follows:

If I am working with two phases, this equation can be written separately for each of the phases.

It is unclear to me which thermal conductivity is used for the heat flux term. In the mixture and VOF models they break down this term to show how an effective thermal conductivity is used. Am I to assume that for the Eulerian model that

q_phase1 = - k_phase1.∇T

q_phase2 = - k_phase2.∇T

where k is the material thermal conductivity of each phase?

]]>I am simulating a simple cylinder in regular waves (frequency domain) in AQWA - Hydrodynamic Diffraction. Here's a picture of the resulting pressures around the body:

The step on pressures on the free surface doesn't seem right. It also doesn't make sense to me that the largest hydrodynamic pressures are on the free surface... I mean, yes, wave action is larger there, but aren't hydrostatic pressures also included in this value, thus, increasing pressures on the bottom?

Any insight is appreciated :)

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

]]>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.

]]>I am trying to follow the tutorial guide of Fluent 18, but I cannot find the `unsteady_compressible_R180.zip`

document, with the files `nozzle.msh`

, `pexit.c.`

Even searching for the tutorial name, I cannot find the files. I cannot create an ANSYS customer portal account as a student, and I am sent to ansys.com/academic where I still can't find the .zip file.

Any help?

Thank you in advance.

]]>I'm trying to write and compile a UDF that only allows rotation about the hinge, but I'm having trouble compiling it. I know ANSYS 20 has the ability to compile UDF's using fluent, but I only have access to Ansys 18.1. I have downloaded Microsoft Visual, and have created a text file "flap.txt" that I converted to "flap.c", but ANSYS is still not reading it properly.

There are no spaces in my file directory, and the "flap.c" file is saved where my output values are stored.

Can anyone provide a step-by-step process for writing a UDF, compiling it using MS Visual, and then importing it to Fluent? I've never done this before so I'd appreciate as much detail as possible!

Thank you!

]]>Hi everyone,

Does anyone know how to estimate velocity v2 in the circular pipe if given the velocity in an upstream annular pipe is v1? t is a very small gap compared to l1 and l2 so the flow travels in a different direction as shown in the diagram.

Initially, I was thinking of using mass conservation so the velocity only related to the cross-section area ratio. However, I am not sure how to account for the velocity loss in direction change and the vortices generated at the turning angle.

Another idea is to use the Bernoulli equation and accounts for the minor losses at the turn and at circular pipe 2. However, I only know P1 at the upstream but not sure about P2.

Any hints would be very much appreciated.

Best regards,

Lugia_06

]]>i am doing a 3D simulation for analysis of droplet spreading behavior on the structured surface.

i have written the udf is attached in the pictures.

To get spreading behavior/spreading factor/liquid-air interface the

"C_CENTROID(e,c0,t0);

r[i]=e[0]; "

is used in the udf.

1) the problem i am facing right now when the droplet hits the structured surface the fluent crashes every time.

2) if I remove that command mentioned above in the udf the fluent runs perfectly.

can you help me to fix this issue?

I need to use this command to get the spreading factor of the droplet impact.

i also attached the udf pictures and geometry pictures in the form pictures.

please reply urgently.

i have a due date of the project in my University.

I have two questions about adhesive melting simulation in Ansys Fluent:

1) When introducing the properties of a fluid in Ansys Fluent, what is the Pure Solvent Melting Heat (j/kg) ?

2) Starting from environmental conditions, would it be possible to simulate a heat flow input until a point or surface reach 150ºC and then remove the heat flow input and keep the temperature (150ºC) constant? Where can I establish this?

Thank you

]]>I am assigning boundary conditions that would simulate this. I want the pipe flow to be at gauge pressure values of 1-5 bar, and at 0.6m/s velocity. Ideally, I'd have a pressure inlet (of say 1 bar gauge), an outlet pressure for the leak (of 0 bar gauge - i.e. atmospheric), and a velocity outlet of 0.6m/s, rather than pressure at the outlet and velocity at the inlet. This is because there is going to be some pressure drop within the pipe as a result of the leak, meaning that the outlet pressure is undetermined initially, but as the leak is sealed, the low-pressure region would be eliminated, and the inlet and outlet pressure become equal (i.e. 1 bar throughout the pipe).

The reason I'd also like velocity to be at the outlet is because within my study, I want to look at the impact which turning on the house taps downstream of the leak (i.e. which would increase velocity within the pipe) would have on the particle's bond to the leak. This is because you can assign a 'detachment velocity' for MPM particles, beyond which they lose contact with the wall, which would cause the leak to become unblocked again - I'd like to know at what velocity this would occur.

My problem is that from what I understand, you can only assign 'velocity inlets' boundary conditions, but not velocity outlets. Can anyone see a way around this, or perhaps a way to redefine my problem? Thanks in advance.

]]>I am new to ANSYS Discovery, and I was attempting to compute the drag force experienced on a design my team created for the F1 in Schools competition. I received the following error, and I cannot figure out how to fix it, "Select one or more faces on wall location for Drag Force. (129 Faces)". I have attached a screenshot of the error to this question. Any help given on this matter would be appreciated greatly.

Thanks,

Conor.

I am trying to simulate condensation of humid air as it passes over a set of cooling coils. I have modelled the fluid as a mixture of air and water vapour and given the corresponding mass fractions (which accounts for the rh). But I am not sure how to proceed with the simulation of the condensation phenomenon.

Can someone suggest a methodology of how to set up this phenomenon using ANSYS FLUENT ?

]]>We were given a simple nozzle model where the inlet has both a specified massflow and a pressure. Is there a way to give both the pressure and a massflow at the inlet in FLUENT ?

Please share your thoughts on this !!

]]>I am solving a two-phase flow problem using DPM(Discrete Phase Model) in ANSYS Fluent. The two-phases are lubricating oil and air. The problem is that I need to input whether it is laminar or turbulent. In order to do that, I need to find the Reynolds number.

For this two-phase flow how to measure the Reynolds number and as of DPM is concerned for what range we can consider the flow is turbulent or laminar (because Reynolds number considered for the DPM model is different from the regular one)? Here I'm solving the problem for a simple pipe of 5mm diameter and 20mm length with a velocity of 6m/s. The density of oil is 954 kg/m3.

Thanks in advance.

]]>At the bottom of the tank there is a 0.05 m diameter inlet and a 0.0.5 outlet, the outlet and the inlet are just in a symmetrical position.

At the same time, there is a metal cage at the bottom of the tank, in which there is a 0.05 meter diameter balloon filled with antifreeze.

I want to know what happens to the pressure inside the balloon and the pressure outside the balloon when( the inlet and outlet velocity of the tank changes very rapidly / the inlet and outlet velocity are at a particular velocity).

I just ask you to provide me with the design ideas, which do not need to conform to the parameters I provided, because I do not know how to simulate the effect of fluid on elastic materials. Elastic materials cannot be set up in FLUNET, and complex fluid simulation cannot be set up in Static Stracture.

thank you for your help.

?

]]>is the volume concentration of the dispersed phase at time step that of 0.001 of the whole volume ??

an what are the relations between the time step for unsteady analysis DPM and Step Lenght Factor?

and finnally in unsteady analysis DPM, in the injections there are another parameteres the initial time and the stop time, how is relate with the unsteady analysis? i think that fluent is nothing clear with all parameters to control the simulation

]]>I am trying simulate a multiphase system ( pure liquefied propane) in a tank under heating using ANSYS FLUENT 2021R1. The tank doesn´t have flow in and flow out, it is closed. I Set 0.95 liquefied propane using Patch. But, ANSYS show me 2 error messages. I have tryed find the solution by myself but I coudnt.

The error messages are: 1- latent heat can´t be less than zero. 2- float point exception.

In my set up, I am using:

VOF+Lee, propane (gas SRK equation for density); two phases; phase 1 is gas; sharp; The material properties are the same as ANSYS database.

suface tension coefficient 0.004;

mass transfer- evaporation/condensation, 1 mechanism, frequency 0.1 (both);

The sataturation temperature I set a polinomial from a databook;

The liquid propane I created from propane (ansys data) and set a polinomial dependent of temperature for each properties (density, viscosity, thermal condutivity and specific heat). Those polinomials equations I got from a Chemical engineering databook. The other properties ( reference temperature, standard Enthalpy and mocecular weigth) I used the same as propane ansys database.

What am I doing wrong?

I aprecciate any help. Thanks in advance.

]]>I am working on a model (mixing elbow heat transfer - 3D) problem using Fluent.

I was wondering how to validate or represent (conservation of momentum) principle using Fluent, I know that for mass and energy we can do it using flux report. But what is the property that checks momentum for such cases.

Thank you all.

I am working with K-w SST turbulence model. Till now I have been resolving the boundary layer using y+ below 1. However now I want to use wall functions to speed up the process. Once I coarse the mesh, how can I activate wall functions?

Additionally, is it okey y+ around 30? What if in some regions it becomes smaller than 30 so it gets in the buffer region? Is the model able to handle that somehow?

Many thanks in advance.

Kind regards,

Fran

]]>I'm trying to simulate the Mixture model for the fluid flow, and DO model for the solar input. In the mixture model, I need to give properties for individual phases, including optical properties like absorption coefficients. For the single phase model condition, it's straight forward to calculate the absorption coefficients (peoples use Rayleigh/Mie theory). For the mixture model, If I give the value of individual value of phases, the results shows a higher deviation, which is lower for the single phase condition. Is there any rule/formula to calculate this optical properties or the mixture condition?

Lastly, In the mixture model, what will be the phase's velocity? Do they require equal velocity, or the dissimilar velocity?

Thanks

Juwel

]]>thanks

]]>I need to use the ekill method .

Can anyone help me over this .

The geometry which i am using is also been attached here.

U can also reach me on-:

I've been working on modelling the HASEL actuator, specifically the peano HASEL actuator ( demonstrated in the following video). https://www.youtube.com/watch?v=-TKjJBZEZe4

I'm having trouble matching my simulated results with the results in practise. before showing how I modelled the HASEL actuator below in Fig 1. shows how the HASEL actuator should look when it is 'fully strained'.

*Fig 1. the desired result that I want to simulate*

I modelled the HASEL actuator in 2D with 3 element types as shown in Fig 2. below

*Fig 2. PLANE183 to represent the pouch (shown by the white board around the actuator)*

*HSFLD241 to represent the fluid (shown in purple)*

*TRANS126 to represent the electrodes force on the actuator (shown in red)*

the mesh seems to me be good, with a few exceptions at the ends of the actuator.

My issue is when I solve the model I can never quite reach the 'full strain' which is effecting my results giving zero displacement where the load would be attached Fig 3.

*Fig 3. a contour plot of the x displacement for the HASEL after a voltage has been applied. The red circle is were the load would be attached and the red square is the corresponding contour displacement value.*

No matter what is do I can not reach that full strain or get any reasonable strain at the load.

I even tried using the 'penalty method' to set the electrodes final displacement to the 'fully strained' position and I got the same result.

I seem to have reached some sort of limit with either the PLANE183 or the HSFLD241 that I can't exceed.

Please let me know if anything isn't clear.

Any help will be much appreciated.

Regards

Levi

]]>I am working on multiphase blood simulations in patient-specific aortas using ansys FLUENT (version 19.1). I have succesfully implemented a two-phase model on different geometries, but am struggling with the interpretation of some results.

I model the blood as being non-Newtonian using a modified Carreau-Yasuda model with two phases: plasma + RBC (as a granular phase). The UDF uses the shear rate of the RBCs and RBC volume fraction to calculate the RBC viscosity and this is then implemented in FLUENT under the specific settings for the RBCs in the granular phase. The bulk viscosity is assumed to be zero. The mixture viscosity is then (when post-processing) calculated according to: mu_mix = mu_rbc*VOF_rbc + mu_plasma*VOF_plasma. The plasma viscosity is assumed to be constant.

To compare and verify my results, I did a single phase non-Newtonian simulation with the same UDF, but using a fixed VOF of 0.45 (therefore, the viscosity is only dependent on the strain rate magnitude.

When I compare the mixture viscosities for the single and multiphase model, I encounter lower viscosity magnitude values for the multiphase model. I have trouble finding a reason why this is the case, since (for as far as I know), the strain rate magnitude is only dependent on the velocity of the particles. There are no differences in the velocity contour plots, so I would expect the viscosity contours to be the same as well (at least during steady state). I listed the differences between the simulations below:

1. Single phase has overall plasma viscosity of 0.0037 Pa s, whereas the two-phase has a plasma viscosity of 0.001 Pa s and the RBC viscosity is determined by the UDF.

2. The single phase model has an overall density of 1080 kg/m3 and the two phase model uses 1025 kg/m3 for the plasma + 1125 kg/m3 for the RBCs.

3. Obviously, the two-phase model has the granular euler-euler multiphase approach enabled. Here, RBCs are assumed to be the granular phase with a diameter of 8e-6 m. Granular bulk viscosity is assumed to be zero, only drag is enabled (Gidaspow model).

All other convergence settings are similar, and the results presented below are from converged steady state solutions.

Also, the UDF for 1) the single phase non-Newtonian model:

DEFINE_PROPERTY(cy_viscosity_singlephase, c, t)

{

float mu_plasma = 0.001;

float eps_RBC = 0.45;

float lambda = 0.110;

float n = (0.8092 * pow(eps_RBC,3)) - (0.8246 * pow(eps_RBC,2)) - (0.3503 * eps_RBC) + 1;

float m = (122.28 * pow(eps_RBC,3)) - (51.213 *pow(eps_RBC,3)) + (16.305 * eps_RBC) + 1;

float exp = (n-1)/2;

double gamma;

double mu;

gamma = C_STRAIN_RATE_MAG(c, t);

mu = mu_plasma*m*pow((1+ pow((lambda*gamma),2)),exp);

return mu;

}

And the UDF for the two-phase model:

#include "udf.h"

DEFINE_PROPERTY(granular_viscosity_rbc , cell , thread_rbc)

{

int phase_domain_index , ID=9;

Thread *mixthread;

Thread *subthread;

Domain *mixture_domain;

mixture_domain = Get_Domain(1);

mixthread = Lookup_Thread(mixture_domain ,ID);

/* predefine variables */

real muplasma=0.001;

real murbc;

real mumix;

real eps_rbc;

real lambda=0.110;

real m;

real n;

real sr;

Domain *plasma_domain;

Domain *rbc_domain;

/* get domain numbers of plasma and rbc */

plasma_domain = Get_Domain(2);

rbc_domain = Get_Domain(3);

/* loop over all threads */

sub_thread_loop(subthread , mixthread , phase_domain_index)

{

/* viscosity in plasma thread is muplasma */

if ( subthread == Lookup_Thread(plasma_domain ,ID) )

{

muplasma = C_MU_L(cell , subthread);

}

else if ( subthread == Lookup_Thread(rbc_domain ,ID) )

{

sr = C_STRAIN_RATE_MAG(cell ,subthread); /* shear rate from rbc, could be the

wrong one */

eps_rbc = C_VOF(cell , subthread);

}

}

n = 0.8092*pow(eps_rbc ,3.) - 0.8246*pow(eps_rbc ,2.) - 0.3503*eps_rbc + 1.;

m = 122.28*pow(eps_rbc ,3.) - 51.213*pow(eps_rbc ,2.) + 16.305*eps_rbc + 1.;

mumix = m* pow( (1.+ pow((lambda*sr) ,2.) ),((n-1.)/2.) );

murbc = (mumix*muplasma -(1.-eps_rbc)*muplasma)/eps_rbc;

/*if (cell %50000==0)

{

Message("muplasma = %f\n", muplasma);

Message("strainrate = %f\n",sr);

Message("vof = %f\n",eps_rbc);

Message("n = %f\n",n);

Message("m = %f\n",m);

Message("mumix %f\n",mumix);

Message("murbc %f\n",murbc);

Message(" %f\n",);

}*/

return murbc;

}

Furthermore, I investigated the effect of taking the strain rate magnitude for the two phase model from the plasma phase / from the plasma + rbc phase. However, this gave no different viscosity magntide if deducted from the plasma phase, and if it was deducted from the plasma + rbc phase, the mixture viscosity was even lower (due to the shear thinning effect).

Therefore, I was wondering: what exactly are all the parameters effecting the shear rate magnitude (and this the mixture viscosity) in a multiphase model? Since everything I read / research leads to the conclusion that it's only a function of the velocity field, whereas those are similar for the different simulations.

I included images of the different Velocity Fields + RBC viscosities + mixture viscosities.

Thanks in advance!

I am trying to simulate different pipe flows with some obstacles inside:

- stationary ones - these cases are often unable to achieve steady state and transient run is needed, but behaviour of a system is not perfectly repetitve over time;
- rotors, which are moved due to forces exerted by fluid flow with use of six do solver - these are of course inherently unsteady

I am dealing with low Re numbers, like 1400, 1900 etc. which are calculated with respect to diameter of a pipe as a characteristic length and this would indicate laminar flow. Medium inside a pipe is water. However, due to unsteadiness of both cases and presence of such obstacles in flow I am not quite sure if I should use a laminar model or tubulent one (maybe even with some transition model turned on?) Or maybe I should calculate Reynolds number with respect to different characteristic length? I would be really grateful for any tips.

Thank you in advance for your help.

]]>At this point, I wanted to go and research LSB (laminar separation bubble). The tests were performed at a Re=1*10^6 (v = 20m / s). Are there any turbulent laminar transition models? Can they be activated with the k-omega SST (Transition SST)? Or is it better to switch to a 3D studio and use LES?

]]>I want to study the dispersion of a pollutant in the atmosphere. My first question is about the relationship between Mass Flow Rate and User-Defined Scalars boundary Value (User scalar0).

And secondly what is the unit of the scalar that gives us FLUENT results.

Thank you in advance for your help.

]]>I'm a mechanical enginering student.I want to learn solution methods in Ansys Fluent.What is the Gradient Methods in Spatial Discretization ? How Does it work Gradient Methods ?

Thank u.

]]>I have an issue when using the Ansys FLUENT Optimizer.

The case is a tunnel, with the water flowing through it.

The top surface is the wall, the bottom surface is wall with heat flux.

The two side surfaces are symmetry.

The objective function is minimizing the temperature of the bottom surface.

I already made a case with smaller thickness proving the bottom surface temperature is smaller, showing in the picture below.

But when I try to optimize the same case, there is negligible change for the geometry and the thickness does not change. (for the optimization, I set the constraint that the geometry could only change in y direction, which is the thickness direction)

I also made vector plots of sensitivity of optimal displacement for this energy case (objective function is minimizing temperature) and case without energy(objective function is maximizing the pressure drop between inlet and outlet),

From the plots, the geometry can not change in y direction (thickness direction) with energy on, but for no energy case, the design will be changed in y direction. These plots are also shown in the picture below.

My question is why the optimizer does not make the geometry of energy on case change in y direction(thickness direction) and can make the geometry of energy off case change in y direction(thickness direction)?

Thank you for any reply!

zyao

]]>