Science topic

# Computational Fluid Dynamics - Science topic

Numerical methods to solve and analyze problems that involve fluid flows.

Questions related to Computational Fluid Dynamics

As we know, the Nusselt number for an isothermal flat plate is written as Nu=h*x/k where h is the convective coefficient, x is length and k is the thermal conductivity of the fluid. In addition: h=q/(Tw-T_inf) and q=k*dT/dy at y=0.

Now, if the thermal conductivity is a function of temperature, then, the thermal conductivity of free stream (k_inf) is different from thermal conductivity at the surface (k_w). For q and Nusselt which k is adequate? I believe that for q we should use k_w and for Nusselt we should use k_inf. Because q is calculated at the plate, but Nusselt is calculated regarding to flow. However, in some papers (not all of them) i see that they used k_inf for both of the Nusselt and q.

What is the best definition for Nusselt number and why?

The equivalent sand grain height approach is widely used in modern Computational Fluid Dynamics (CFD) calculations on rough surfaces. I am conducting a few simulations against available experimental data on a rough aerofoil. The experiment reported the rough surfaces were sandpaper P80 and grit 36 without mention the equivalent one. Surface roughness research is not a field I'm familiar with, because I concentrate on roughness modeling in aerodynamics. So I tend to ask if any one who knows any data or correlations to sandpapers. Don't mentioned the method in Boundary Layer Theory by Schlichting, because the experiment didn't provide me sufficient data to use that. Dirling's correlation is also not viable because I can't do the roughness geometrical measurement.

I am working on optimising the design of the static guide vanes found encasing a vertical wind turbine however I am finding it difficult picking out aerodynamic theories that would be relevant to this area of study. Any suggestions would be welcome.

What is the right way to change the moisture content of the grain from wb% to mol/m3 to put the initial and equilibrium moisture contents in COMSOL?

Why are pressure and specific enthalpy commonly the choice of state variables when modeling two-phase thermal-hydraulics?

Why not use specific internal energy or entropy instead of specific enthalpy?

Any basic book to understand the code of a Lattice Boltzmann Solver for CFD? I basically want to use XFlow.

The Euler equation is used with vorticity confinement methods.

I have to simulate a feed nozzle design for FCC (Fluidized Catalytic Cracking) column in a petroleum refinery. It is a multiphase problem. For this, I am asked to choose the most appropriate simulation package b/n COMSOL and FLUENT?

Can anyone help me in this regard by sharing your views on which is best for solving such cases?

Considering a fully developed flow in an annular pipe. The velocity is only a function of radius. What a bout the pressure? I know the pressure is a function of pipe length. Is the pressure also a function of radius?

I know how to bilinear interpolation in a unit square grid but I am struggling to find bilinear interpolation involving radial and direction(angle)

I need some suggestions on CFD Analysis of microturbine ( speed above 1,00,000rpm)..

i am planning to use ANSYS-CFX as i need to proceed with FSI of blades after getting forces from CFD..

Details- Curved blade rotor, 8 blades, axial flow, clearance btw wall 1mm.

I am planning to use sliding mesh to the rotating interfaces since unsteady conditions may exist.

My Query- How to mesh fluid and solid region, whether rotating parts alone meshed separately or stationary volume also need to be meshed along with it..

Does it requires to define the boundary btw blades and hubdisk since both are rotating..but separate..

I am using Sliding mesh for first time,, looking for some tips

I have been working on rotor and propeller blade modifications that shift L/D and also Cd at high and low AoA respectively. The work is focused on rotorcraft at present, with rotor diameters from 25' to 65', symmetric and asymmetric blades. Are there any testing programs involving HAWT blades with diameters from 60' through to 180'? The boundary layer modification that is being employed indicates that some rotor models such as Camrad II are not suitable to a CFD analysis of the dynamics involved.

Give your personal opinion for others to read.

I wish to make a simple program that solves tridiagonal matrix . now TDM can be solved using Thomas' algorithm, which is very serial in nature. I have come across cyclic reduction , even-odd reduction method in one of nvidia's papers. Can some one please explain me this algorithm, and help me with the pseudo code?

I am working now on the grain drying with CFD simulation using Comsol and I need to start with one kernel simulation for moisture transfer during drying. This is the first time for me to use the Comsol. So, How can I start?

I have been trying to simulate droplet falling, impact and spreading. I have used COMSOL and Fluent. I got some results but they are not satisfactory. Is there anyone who worked on similar things? I need to :

1) define an initial velocity of the droplet

2) apply dynamic contact angle during spreading

For COMSOL, the droplet don't deform that much after the impact.and for fluent I having trouble defining a free / open boundary. I have been using pressure inlet for free boundary. Here is some simulation result.

1. VOF+Level Set - with surface tension - with wall adhession (http://www.youtube.com/watch?v=P4VkHX9UYeE)

2. VOF+Level Set - with Surface Tension - no wall Adhession (http://www.youtube.com/watch?v=4UVQ-AM-vkY)

3. VOF (no Level Set) - without surface tension - no wall adhession (http://www.youtube.com/watch?v=rtVbNEHD6zE)

Can anyone help me regarding regarding my queries?

1. How can I assign initial velocity for the droplet?

2. How can I get more realistic deformation?

3. How can I apply wetted / non-wetted surface condition?

4. How do I implement dynamic contact angle?

Can anyone tell me whether Smooth Particle Hydrodynamics (SPH) is a better option for this problem?

What is the relationship between the lift coefficients of upper and lower transition points for the surface of airfoils at increasing AOA up to 10?

In the upper surface of airfoil, transition occurs in 30% chord and moves towards the leading edge and pressure side 40% chord from the leading edge(moves towards trailing edge), the lift value increases up to 10 of AOA. What is the relationship of upper and lower transition points with lift coefficient?

I have meshed my design model but i am not able to export it to fluent (CFD). Everytime it displays an error in fluent. Please guide me.

I want to solve a CFD problem with a mesh generated by my own code in OpenFOAM. The question is: in what format is better to export the mesh for OpenFOAM?

Total drag is sum of viscous and pressure drag . code Cdp and Cdf in C++??

I'm not very clear about the no-through condition and no-slip condition. When I write programs to do the impulsively started cylinder simulation, I found that after convect the particles, a few enter the boundary. I want to know whether the no-through condition should take into account this time and how to do it.

How can we raise the limits of integration for a triangular element in cylindrical coordinates in FEA? How are the limits in the radial and tangential direction?

I am looking for software for wind simulation for Mac OS. I use Ansys but I heard that there is no version for Mac. Is there any other software that you are satisfied with using? Is there a free version for students?

Is it possible to diagnose a disease from mechanical properties of blood ?

I am a Student of M Tech (CFD) and working on Nasal Airflow simulation. I want to prepare a 3D geometric reconstruction of Nasal cavity. The computer tomographic (CT) images are used to obtain 3D model, but I dont know how ? Can anybody help me by explaining how these images are processed to get 3D model and is there any software used in medical technology to convert into 3D model ?

I calculated the flow in arteries and I would like to show that for some time steps the wall shear stress has the opposite direction, for example in the curves, branches, etc. For the straight pipes it is easy but how to do it for the more complicated geometries?

I'm a CATIA V5- beginner. I have designed with CATIA V5 a 3D re-entry capsule. The surface of the capsule is not straight but curved similar to a spherical surface. The Purpose is to integrate and connect this model with a grid generator and then perform as generic CFD model simulations.

Of course for numerical simulations I have to define a "far-field" for this model for example for a spherical model. Regarding this matter I have two questions with please for your support:

1) How can I define using CATIA v5 more extra-circular surfaces on this sphere surface for a side jet, so that the circular surfaces exactly to be placed on the curved surface of the sphere?

2 How can I define then to this spherical - model a solid room for CFD simulations as a "far-field"? Then the generic model (capsule) overlaps or intersects with far field as a solid volume then is a problem or not?

My question is related to different softwares/tools that we use to predict the temperature rise in the Electrical distribution enclosures such as switchgears, motor control centers, etc

Apart from various ANSYS modules like Themal/CFX/Fluent, etc. do we have any other popular packages which we can use to predict temp rise ? If yes, how do we compare the solvers performance with ANSYS ?

I looked up through the literature and I ended up with a work done by Olsen H. and here is the citation "Olsen, H. (1970). Unpublished sloshing experiments at the Technical University of Delft. Technical report, Delft, The Netherlands." However, I was not able to get this reference.

Because Fluent is a commercial code, it is not always good to use the default turbulence model inside for research purposes. To define an omega equation based turbulence model, in Fluent, we can choose the k omega model, define our own user defined scalar (UDS) transport equations, and then solve the newly defined transport equations instead of the default k omega model. The k and omega values are also necessary to be copied back to the default k and omega field, because the momentum and energy equation needs the value of k and turbulent viscosity (computing the unknown Reynolds stress) as well.

So, my first question is, is there anyone has done similar things before?

I managed to write an UDF to define all necessary UDS, boundary conditions, and initialization, but I find the k and omega jump to negative values in some region of the flow field. Linearization of the source term, limiters for k and omega may help, but I don't exactly know how to do it. So, my second question is, how to deal with the solution divergence when using UDS k and omega equations.

My ultimate goal is to define all k omega based turbulence models, such as SST, and γ-Reθ SST.

I am researching biomimetics of fish and sea creatures, especially their motion. Any paper, documentary, or piece of information would be useful for me.

I am trying to understand the idea behind motions of fish and sea creatures, regarding efficiency and hydrodynamics.

I want to model the propagation of a flame front using MATLAB. What model can be used? Any references from where I can get information?

I think mesh-based methods can be completely replaced by mesh-free methods, but maybe mesh-based methods such as FEMs have some useful properties that mesh-free methods don't have them.

Comparing Wind Tunnel Tests with Fluent Results - Dimensional Modifications

I have taken wind tunnel experimentation for 20 cm chord and 25 cm length airfoil, and want to compare the results with 1 m length and 20 cm chord of airfoil in FLUENT.
Lift and drag are inversely proportional to the lift and drag coefficient. Is this right or do I have to model for 25mm length of airfoil?

I am working on an analysis in which oil flows through a tube and causes a turbine to spin. I would like to add friction between the spinning turbine and the shaft as it is spinning around.

Currently, according to CFD, the turbine is spinning at over 7 million RPM at average flow which seems completely impossible. Any insight on this matter would be greatly appreciated.

I have a reasonably complex experimental electro-mechanical hydraulic system (using water medium) design I would like to have simulated (to include pressure and flowrate versus time response, valve operation - steady state and transient) before I spend a lot on hardware to build it. If anyone has any connections/suggestions, please let me know.

ICEM CFD help needed

I modeled wind turbine blade in solid works and meshed with ICEM CFD. After naming the parts, while meshing: "The application has run out of memory and will terminate after doing an emergency save". My system has configuration of 3GB RAM and 320 GB HD. Can anyone help me with this problem?

I am doing analysis of centrifugal pump in turbine mode. I meshed model in turbine mode. Then exported in Gambit for boundary conditions. Then read mesh file in fluent and done 3 D analysis. After doing complete analysis I closed fluent. When I start fluent again and read cas and data file it shows error of grid interface. It shows like this:

Building...

mesh

Error: %%create-sliding-interface: wta(sb2-id)

Error Object: sb1-id

materials,

interface,

domains,

mixture

zones,

default-interior:014

default-interior:001

default-interior

inlet

outlet

outlet_pipe_wall

casing_walls

wall

interface_1

interface_2

interface_3

interface_4

Skipping zone wall-18 (not referenced by grid).

Skipping zone wall-19 (not referenced by grid).

wall-21

wall-22

casing

impeller

outlet_pipe

interior-17

interior-20

Error: CDR: invalid argument [1]: wrong type [not a pair]

Error Object: #f

To better understand the discretization and also to narrow the mesh independent test.

of temperature, the model doesn't seem to handle the heat produced by Joule dissipation. It is going further

I have been asked to represent a rectangular shape as a mesh. I am doing a numerical work which deals with flow inside tanks in case the tank subjects to external excitation. The dimension of the tank is considered to have 104 points in x-direction and 60 in y-direction. Does anyone know how can I handle this task?

Velocity profile is a factor, that you could find the velocity in any depth of fluid by changing the variable.

I would like to verify my FLUENT model for the dam-break process on a positive slope (upward, like a beach). But my reservoir is in the horizontal plain. Can you suggest some literature for this purpose.

Secondly, can dam-break be modeled with laminar flow conditions (instead of turbulent k-epsilon model)?

I am learning to develop algorithm for flooding and drying. And am using the 2D shallow water model.

When I compile the code (written by Stephane Popinet), I am faced with a code warning like "max residual...". A screenshot is attached.

In CFD for which applications do we take the conservative governing equations and for which applications do we use the non-conservative governing equation?

I made a model on CATiA V5 and I am facing difficulty in doing the analysis part. I really do not know how to do the analysis. I haven't used Gambit or fluent before.

I am using the SSME geometry to perform a CFD analysis for the flow characteristics, thrust and plume. I am using an Inviscid density based solver with 20 MPa and 3500 K for my inlet. I am having difficulties in defining the pressure and temperature at the exit. Also should I be using a different type of solver (i.e. Pressure based SA Modle, etc.)?

How can I simulate multi bubble cavitation in comsol 4.2?

I have a system with multi bubble cavitation, and I want simulate the bubble dynamics include the Bjerknes force (first and second).

Hi,

I have a set of PIV vector data recorded at 5000 Hz (!), representing a flow field around a bluff body. Downstream of the body, the flow seems to be turbulent. I want to find out, if the flow has an impact on small droplets. Therefore i want to calculate the Stokes number St=(Droplet relaxation time)/(Kolmogorov time scale). It is no problem to calculate the droplet relaxation time, but for the Kolmogorov time I need the turbulent energy dissipation (epsilon). Epsilon is difficult to calculate from the PIV data, since spatial and temporal resolution are limited. Today a collegue told me someting about an analogy between the Kolmogorov time scale and a Reynolds time scale (?). He said something about Reynolds time being about six times larger than Kolmogorov time, but I was not able to find his equation in literature.

Has anybody a helpful comment on this topic? Is there a way to approximate the Kolmogorov time scale?

Greetings,

Greg

I mean there is any simulatio program or softwear can do it simulatio for bod human or for any part of body?

What are the boundary conditions that should be imposed in order to obtain the simplified momentum, energy equations for shock waves? Is it possible?

Are there any published results for experimental data of measurement of skin friction drag of a triangular plate at zero angle of attack?

Also, can we use theories developed for solving boundary layer over a flat plate (like blasius equation) to estimate the skin friction drag over a triangular shaped plate at zero angle of attack?

Thank you in advance!

Problem in Multiphase Modelling

I am working on simulation of solar still (water purification with help of solar energy) in FLUENT by using multi-phase modelling..Need some guidance.i didn't found the rate of mass transfer from vapor to liquid..i am using Mixture model,3 phases (air,liq,vapor), k-epsilon turbulence model.
Thanks
Vaibhav Rai Khare

Anybody know about Wind tunnel modification project details? What are the data types I should know for that?

Wind tunnel modification and analysis in which software and fabrication is best.

Sir I want to validate this paper. PDf attached.

I have a Simple Flow Situation If you can give a minute , It will Be Solved and my life will be a lot easier.

I have a 3d duct, with a small obstruction/wing to create disturbance.

, Walls are at 400 k constant temperature.

and air at 0.8 m/s at 300k.

the duct is 21 x 14 X 160 mm.

well they are two parallel plates that are 14 mm apart. and the side are open , which are at 21 mm, i have defined symmetry.

It is similar to tutorial "Forced Convection over a plate""http://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Forced+Convection+over+a+Flat+Plate", except, that , that my problem is in 3 d .

Most of friends have replied me like this " As far as finding nusselt number, that is the only way of doing it. ie. report surface integral and manipulate them in excel and then plot. "

i use h*x/k along a line at the bottom plate in its mid, but that gives the local axial variation i think.

but i need average, without using exel if possible.

Anyone intrested in seeing the *.cas, *.dat, *.lay files can mail me, i will send the files so that one can check properly.

Regards Saksham

+919467704656

any help on Tecplot or Fluent is welcome.

Hi... I am modeling open sea air turbulence (Re ~ 6.0e6) using SST (Menter) K-Omega RANS based turbulence model. What should be turbulent intensity (T.I.) at inlet? 1%, 5% or 10%? Also, does anyone have experience on influence of drag prediction for different T.I.? What's the physics correlating T.I. and Drag?

I'm trying to simulate the response of an instrument to an input signal using MATLAB. To be specific its a constant temperature hot wire anemometer and I'm interested to simulate its dynamic response. For the input signal I'm planning to take in data from FLUENT(simulation of flow around a cylinder). For this I need the data of a particular point in the flow field. I wanted to know the procedure to import the data of a particular point in the flow field

For example, there is a strip placed in center of a room, and is a high frequency noise source. Does the code allow to simulate the effect of this noise on the surrounding flow?

Thanks in advance!

I am proficient enough in programming using C and MATLAB but when I open any CFD text book, all i find is calculus. I want to slowly learn writing my own code but the books don't give any idea how to proceed with those hifi mathematical schemes.

I collected raw data from the field and intend to generate a function from the data, how do I do that?

I am interested in solutions of Nonlinear hyperbolic conservation laws with jump conditions (propagation of shock wave).

now days i carried out simulation of flow pst circulare ,square ,triangle cylinders by using fluent

Can anyone help me in Computational modeling of Wind Turbine's Wake? I am just not sure to how to start this project in 2D? assuming an actuator disc doesn't always work... any new ideas?

Is there anyone that conducted research on supersonic caviyt flow with FLUENT or other CFD codes?

or, is there anyone interested in this topic?

I need help in sector , trimmimg and mapping method of combustion analysis of Diesel engine

Hello,

I would like to know if somebody is dealing with this kind of simulation. I did not find any studies concerning this particular subject in CFD. My main issue is to know the forces acting in the human body when it impacts the water. Since I did not find anything more similar, I'm just trying to make a correlation with the slamming studies for boats, but too many assumptions must be made, and I'm afraid I'm not being too precise...

Can anyone help me by telling me some reference or ideas?

Thank you very much

Anyone have experience with ELMER? I have recently begun trying to use it for high pressure gas dissipations.

Evaluation Journals in the field of CFD, fluid mechanics

I would like to have some Journals in the field of CFD, fluid mechanics evaluated like this:
Journal Name Publisher Review Time Revision time Publ. Time Total Time
The CFD J. example publ. 2 months 3 months 1 month 6 months

I am working on a turbulent flow, I have read about enhanced wall treatment which is used to capture viscous sublayer. At very high Reynold's number (~10^7 or ~10^8) does this needed to be captured as this will be very small and may have less effect?

I am trying air injection to a normal flow of water over a flat plate to see the reduction in drag, what model must be suitable, VOF, Mixture, or Eulerian? Speed of water over plate is about 14-20 m/s. and length of plate is about .80m which makes Re~ 10^7.

1. When the liquid content between grains is small, liquid bridges are formed at the contact points of grains and create the meniscus models.

But I can't imagine where the liquid bridges would be generated when the liquid would flow into the grains. Which grains will be included? That is to say,

How is the connection between the grains generated? Is there a theoretical basis to explain this phenomenon?

2. When the liquid content between grains is small: how to calculate the liquid bridge force accurately?

When the liquid content between grains is more or almost saturated, how to calculate the suction due to the pressure difference between the air and the liquid?

Some references to explain this phenomenon would be very helpful.

3. We know that the wet granular materials can express complex phenomena, such as the repose angle can be larger than 90 degree.

But I wonder that whether cohesion is enough to express this phenomenon? Or should we take the lubrication of solid-solid friction caused by liquid into consideration?

If we want to simulate long period case, we must use time scale to reduce our simulation time. But, I still dont understand the effect of NS Equation. How is the effects?

I am trying to simulate BL transition on a flat plate at 50.1 m/s and 0.18% Tu. The plate is 1.8 mts long. Although, I detect transition on the plate it is way too early and is not correlating with the paper whose simulation I am trying to repeat. This is extremely strange because I have followed their instruction and have set the mesh parameters right with a y+ of 0.1. (I have mirrored the authors mesh). The only difference is they are using the SST gamma-theta model in STAR CCM and I am doing it in FLUENT.

Does anyone have any suggestion on how to improve the simulation? I am attaching the reference paper. Please see figure 3 in the attached paper and Case 1-TSK.

I am using k-epsilon model , is there a fluent tutorial available

I need to generate a mesh over the surface of a 3d object consisting of a number of intersecting cylinders. This needs to be done repeatedly, within the loop of an optimization. I'm hoping there is a simple and free tool out there that could handle the task, so I wouldn't have to make my own. (Panelizing the cylinders is easy, but making an algorithm to deal with panelizing the intersections would be too complicated to code myself.) Are there any such software tools out there? Ideally something that could be called from within matlab or a c++ code?

Idea of learning a analysis software.. Which among the four is best with respect to application, popularity, useage and user friendly? I learnt Ansys structural and thermal analysis but yet to learn Fluid Analysis... Hyperworks is mainly for meshing but anyway I include it too... Please suggest me with better options..

I want to take results of pressure distribution on wind turbine blades, I modeled by solid works.

In my college Ansys 12 version is available. I need materials for meshing and analysis (fluent). Kindly suggest and send the tutorials related to my analysis.

I am solving lid driven cavity using fvm and am having issues regarding scaling the residuals.

I want solve by shooing method but I am not getting it. We can also use F''(-infinty) =0;

and F''(+infinity) =0; can anyone help?

Does anyone know how to time-average NO mass fraction in FLUENT?

After running combustion transient simulation, I enabled NOx model and turned off all equations except NO. Then, I continued the iteration.

However, NO mass fraction, concentration and rate of production being calculated appeared in the data sampling statistics. So, I could not get their time-averaged values.

Please kindly give me some suggestions.

I am writing a cfd code for solving N-S equation on a structured collocated grid (lid- driven cavity), my code is slow because of the above reason.

I am injecting air over plate over which water is flowing(see domain attached), since vf = Qa/(Qa+Qw), Qw and vf are known through this Qa is calculated, and since air inlet dimension is known so velocity at inlet is calculated, but vf should i give at inlet in simulation in fluent, is it 1 or less than 1 or what value.

How can I model a 2D aerofoil with flaps?

Supercritical aerofoil with trailing edge flaps

Materials that can be useful.

I have to simulate a THREE PHASE SEPARATOR in which water+air+chemical enters into the chamber and water is to be taped out from one (01) OUTLET

and Air from second (02) OUTLET and chemical remains in the chamber...

***The problem here is that MIXTURE is set on all boundary conditions as well as on OUTLET. I am unable to select any one (01) fluid at OUTLET using FLUENT.

Can FLUENT Simulate this problem?

How can you determine a global Damkohler number in the case of chemical non-equilibrium flow with many reaction steps?

Is it possible to determine a single chemical characteristic time for a non-equilibrium flow?

I'm working on elliptic geometry that is made to rotate at a distance from the central axis of the duct. I need to determine the local and average Nusselt number.

The values being generated from FLUENT are too low

Most of the papers I have read say that in the absence of pooling, the boundary condition at ground-level is given by a flux, something like q = K(dh/dz + 1). But I have not found how to specify what q is. It seems to me that it should be related to the humidity, and also the current level of saturation at the soil surface. Is there a common consensus on an elegant way to describe this boundary condition?

What is the main reason for this prompt to came when a simulation is being done on FLUENT

how exactly is volume fraction defined in FLUENT,

or

if volume fraction of a =Qa/(Qa+Qb), then how can this be related to FLUENT

Is there some handbook in which I can find density dependence on the temperature for liquid alkali metals, especially for lithium, sodium, potassium, and cesium at coexistance line?