# Fluid Dynamics

• Are the governing equations of ECLIPSE 100 software based on Laminar flow or Turbulent flow?

Can this software simulate and analyze the transition of flow through Porous Media? (Single Phase Flow)

Maddali V S Murali Krishna · Chaitanya Bharathi Institute of Technology

Eclipse, a blackoil simulator that can be used to model one, two or threephases.
It’s a fully implicit simulator that can handle gas condensate options. It is suitable for laminar, transcient and turbulant flows

Ref:utahflowcytometry.files.wordpress.com/2012/05/flow-basics-2012.pptx

• Pressure differential sensor for stream flows?

I'm after a sensor to measure the difference in pressure between two areas of flow. Can anyone direct me to a sensor I can buy, or schematics to construct one? I want to measure the difference in pressure between the stream bed surface and subsurface. Thanks in advance

Maddali V S Murali Krishna · Chaitanya Bharathi Institute of Technology

The information may be useful tor your research

Differential Pressure Flowmeters
The calculation of fluid flow rate by reading the pressure loss across a pipe restriction is perhaps the most commonly used flow measurement technique in industrial applications (Figure 2-1). The pressure drops generated by a wide variety of geometrical restrictions have been well characterized over the years, and, as compared in Table 2, these primary or "head" flow elements come in a wide variety of configurations, each with specific application strengths and weaknesses. Variations on the theme of differential pressure (d/p) flow measurement

Ref:www.omega.com/literature/transactions/volume4/T9904-07-DIFF.html

What is the most general available expression of a three-dimensional biharmonic function?

Biharmonic functions f (∆∆f = 0; ∆: Laplace operator) are used as components of Galerkin vector, in the mathematical treatment of problems with stressed solids, at equilibrium. I have found personally expression of the form (... + a/(k.x) + a0 + a1(k.x) +a2 (k.x)2 +...) exp(i k.x), where k and x are three-component vectors, k.k=0, and ai are complex numbers. I am currently using this expression but I wonder whether there are other available more general forms.

Azat Latypov · GlobalFoundries Inc.

For the entire 3D space, one broad family of biharmonic functions are the functions of just 2 Cartesian coordinates derived from a pair of complex analytic functions - see http://en.wikipedia.org/wiki/Biharmonic_equation#2-dimensional_space

How to develop MATLAB code for two-dimensional overland flow problem using Diffusion wave approach?

I am trying to develop a MATLAB code for the two-dimensional overland flow problem using a diffusion wave approach (details in the attached file). But I am using a numerical problem of titled V-catchment (Di Giammarco et. al. 1996) for my study. I am having some problem in my MATLAB code. So any guideance, hint or sample program will be very helpful to me to understand the problem.

Thanking you!

Michael Dada · Federal University of Technology Minna

Hi Ravi,

I read the paper and i guess the equation does not look like diffusion problem (at least for the forms I am familiar with). Meanwhile, i have the feeling that the problem may be treated as a 2D diffusion problem in which the water content is treated like concentration. Analytical approach may be employed if you are ready for the rigour since it allows you to have control and flexibility in the MATLAB code. Luckily, the  attributes including the soil, geological and climatic conditions may be lumped into the inhomogeneous parameters in the equation.

How can I remove bubbles in a micro-channel?

A silicon chip was inserted into the channel, then bubbles were spotted on the surface of chips, which blocks the liquid. So how can I remove bubbles.

Tillmann Krauss · Technical University Darmstadt

just a few tricks, you can try.

use a liquid with less surface tension than can be diluted later with the designated liquid (IPA + water?)

Ultrasonic exitation can help but easily can damage micro structures.

Pulling low pressure on both ends (vacuum) of the channel will expand bubbles. Cycling with normal flow can remove the bubbles.

How to increase the alignment of PDMS plasma bonding?

Three pieces of patterned PDMS are used to form a microfluidic channel,how to increase the alignment?

Nannan Li · Peking University

Thx

How do I determine radiative Nusselt?

The heat radiation flux value determined by fluent Qr
Nu (rd) = Qr.H / (lamda * delta t)

But determined by the value calculated, Nusselt is very large.

How do you do it?

Subhasish Mitra · University of Newcastle

@ Giovanni Maria Carlomagno

Is it appropriate to calculate conduction heat transfer for gas between the two plates in your above example by using the distance between the plates?

The concept of conduction should only be strictly valid in the diffusion regime i.e. boundary layer closed to the plates (walls) and not beyond it as natural convection would be established and essentially we then need to account for convective heat transfer mechanism there.

How to determine the length of convergent and divergent nozzle ?

Currently I'm designing convergent and divergent nozzle for flow analysis. I fixed the included angle for each side. I want to know the relationship between the length and diameter of nozzle. How can I determine the length for each side.

Alireza Ramezani · Sharif University of Technology

you must read text book on Gas dynamics.

Do you have any idea about how to measure real time surface forces on a canoe paddle wing?

The critical area marked on the photo.

Amr Soliman Mohamed · Minia University

Dear Béres Sándor

You can benefit from the following locations

- http://www.biometricsltd.com/semg.htm?gclid=CLeo3NKGwcICFcPJtAod6iMA_Q

- http://www.cometasystems.com/cometasystems/en/

- http://www.delsys.com/products/wireless-emg/

How does 'lambda 2' (eigen vector) becoming negative detect vortex core region?

This is with respect to the vortex core detection and lambda 2 criteria. I did not get the mathematical significance.

Raffaele Salerno · Meteo Operations Italia - Centro Epson Meteo

The lambda 2 criterion concerns the definition of the scalar lambda2 and how turbulent structures can be represented by proper isosurfaces of lambda2. The scalar lambda2 is defined as the second (in magnitude) eigenvalue of the matrix:

Sik Skj + OmegaikOmegakj

where Sij is the half of the summation of partial derivative of ui respect to xj and uj respect to xi and Omegaij is the half of the difference of partial derivative of ui respect to xi and uj respect to xi.

This requires the construction of a characteristic cubic equation and its resolution in order to obtain lambda2, i.e. lambda2 is the second solution of the cubic characteristic equation.

For coherent structures the matrix above can be related to the opposite of the pressure Hessian matrix. As this matrix is real and symmetric, it has two positive eigenvalues when the pressure is at minimum. As a consequence, the matrix above has two negative eigenvalues and lambda2 is certainly negative.

Of course you know that the definition of what is a coherent structure maybe quite vague but it is somehow related to that fact that the life of a vortical structure must be at least greater than the characteristic turnover time. Therefore, once identified some vortices with the lamba2 criterion you have just a snaphot at a fixed time. After some time some vortices will be dissipated rapidly, others can be considered coherent beacause they will be alive for a sufficient time. You could explore the spectral energy content in time and discovering if some energy peak remains relevant for some time.

The use of the above matrix is more pratical than the pressure Hessian matrix since t involves low order derivatives instead of pressure second derivatives.

How can I deal with staggered grid boundary conditions?

I'm using a semi-implicit code and I don't know how to deal with boundary conditions of staggered grids at the implicit part of the code. There is some book that can help me?

Garry Riviere · University of La Réunion

You can find boundary conditions implementation in An introduction to computational fluid dynamics. The finite volume method. H. K. VERSTEEG and W. MALALASEKERA.

Why I am getting different solutions when I am trying to plot the logistic system with oscillation using MATLAB?

I am trying to get the 3-D plot of the system above using analytical and numerical solutions, but I got different solutions. I am using different values for omega and the growth rate.

Avan Al-Saffar · The University of Sheffield

The system is:

dp/dt = N0 * sin(omega * t) * p * (1-p/k) ;

The attached file is the analytical and numerical code that I wrote to find the result in MATLAB,, for the short period I am getting the same result but when I increased the time vector ,,There is a difference appear between the results.

• What is the equation to calculate the rate of heat transfer of a Closed loop Pulsating heat pipe ?

I am working on Heat pipes. I need this equation to improve my design.

Maddali V S Murali Krishna · Chaitanya Bharathi Institute of Technology

This information may be useful for your research

Pulsating heat pipes have received growing attention from experimental and theoretical researchers inrecent times. Behind its constructional simplicity lie the intriguingly complex thermo-hydrodynamic operational characteristics. Part A of this paper has presented the thermal performance results of a fairly largematrix of closed loop pulsating heat pipes. This paper, which is an extension of the previous work, firstpresents some more visualization results to highlight the complexities involved in mathematical formulation of the modeling problem. The phenomenological trends recorded in the visualization set-up are fully inline with the previous quantitative data of Part A. Critical review of the existing modeling approaches to CLPHPs is presented in the wake of these results. A detailed discussion follows on the important issues involved in the mathematical modeling of these devices. Then, semi-empirical correlations based on nondimensional numbers of interest for predicting the thermal performance of CLPHPs are presented. Althoughthere are limitations of the models presented herein, modeling by non-dimensional numbers seems to be most promising as compared to other existing techniques

Closed loop pulsating heat pipes
Part B: visualization and semi-empirical modeling

Sameer Khandekar , Piyanun Charoensawan Manfred Groll  , Pradit Terdtoon

Applied Thermal Engineering 23 (2003) 2021–2033

home.iitk.ac.in/~samkhan/Bio_data/publications/Khandekar_4.pdf

Are static pressure and absolute pressure the same in magnitude?

I am aware of the individual definitions of both static and absolute pressure.

Will the magnitude of static and absolute pressure be the same, even though  definition wise they represent different concepts?

A.O. Borisyuk · National Academy of Sciences of Ukraine

OK! Come on, work and don't be obsessed with anything more!

Can you explain about wall boundary?

Hi, what is difference between non-slip and slip boundary at wall... give a physical and mathematical details about that....

Salaisargunan S P · Pusan National University

THANK U SO MUCH TO MR, PUTU HARRY. G

According to which mechanism do cavitation bubbles enhance atomization characteristics?

Are there any analytical equations or theories that relate the final droplet's SMD to the mechanism by which cavitation bubbles improve the spray emerging from plain orifice nozzles into still air?

Belkacem Abderrezzak · Beijing University of Aeronautics and Astronautics (Beihang University)

Hi Baris,

i really appreciate your kind concern and a directives!

thank you a lot.

Sincerely.

Belkacem

How do I specify system temperature and Arrhenius rate constant in FLUENT?

Hi all!

I have a problem in FLUENT which I am describing below.

I have a batch reactor where a volumetric reaction is taking place with finite rate law and Arrhenius reaction rate. So I have specified the activation energy and pre-exponential factor in the reaction panel. It will access temperature from the system.

Where do I specify the system/operating temperature? Is it in initialization section?

Do I have to patch the temperature in the cell zone, or in the operating condition section?

Thanks,

Vivek.

David Rathnaraj Jebamani · Sri Ramakrishna Engineering College

You can try the Discrete Phase Model (DPM) , However an UDF may be required to specifically address the species issue .    Try the Species Transport Equations from fluent manuel

What is the effect of porous layers on Drag coefficient for flow around cylinders?

In the simulation, a porous layer with a constant thickness is added around a circular cylinder. As a result, the drag coefficient increases by increasing Dracy number. Is this true? What is your idea?

These results are exactly against the same condition for flow around square, where the drag coefficient decreases by increasing Dracy number. (for flow around cylinder, the separation angle increases by decreasing Darcy number... )

Ahad Zarghami · Delft University of Technology

thanks Nicolas

How do you write the Kasuda equation UDF in ANSYS Fluent?

Can anyone help me to write a Kasuda equation UDF in ANSYS Fluent

The equation is shown in the below link.

Where Z is the ground depth (in meters) and Ƭ is the time (in day). Other parameters are given.

Sorry, I have no idea; this is not in my area of expertise

What is the problem associated with the Navier-Stokes theorem?

I want to know this problem in simple words , if anyone can help me ?

Alexander Nee · Tomsk Polytechnical University

Despite pretty simple notation for the laminar flow at the first sight, nowadays analytical solution isn't been obtained. Far more difficult with turbulent flow. The number of unknown variables exceed quantity of equations.

How does pressure effect flow behaviour in two-phase flows?

I am investigating the effect of pressure on two-phase oil-gas flow behavior using CFD techniques for my university dissertation. I am looking for any articles or information which may aid me in my literature review, specifically on how this may affect the transitions between separated and intermittent flow or how the intermittent flow region is affected. Is anyone able to recommend any particularly good articles?

The justification for my research is due to the high pressures found in deepwater reservoirs.

Daniel Alecu · Pratt & Whitney Canada

I suggest a search on "Two-phase flow speed of sound". A relatively small bubble content in a liquid flow can significantly reduce the bulk modulus thus the speed of sound. In case of a disperse liquid in gas, the liquid increases the density of a very compressible flow reducing again the speed of sound. In a nutshell, one may expect low speed of sound in the mixed flow in a fairly large range of conditions and reaching critical flow condition could be expected. For example, a ~12% water dispersion by volume in air reduces by 10x the speed of sound (34 m/s instread of 340 m/s).

What's the best method to visualize the vortex structure in a boundary layer?

I recently simulated the early-stage of the transition of the flat-plate boundary layer. I have tried to plot the vortex lines but the results are something messy. I wonder is there some simple methods to clearly show the vortex structure?

Heinz Herwig · Technische Universität Hamburg-Harburg

The lambda_2 method is well established, you may however also visualize the lical entropy production,as explained in section 2.3 of:

Y. Jin, H. Herwig: From single obstacles to rough walls: Some fundamental investigations based on DNS results for turbulent channel flow, Zeitschrift für Angewandte Mathematik und Physik (ZAMP), Vol. 64,1337 – 1352, 2013

H.H.

Does the RK equation of states predict a higher density ratio or CS in a specific reduced temperature?

For a two-phase flow and in a specific reduced temperature (e.g. Tr=0.75), does the Redlich–Kwong (RK) equation of states predict a higher density ratio or Carnahan-Starling (CS)?

Ulrich Deiters · University of Cologne

You can use many EOS for water, the official one is IAPWS, a multipararameter reference equation. To try it, you can use the ThermoC website; there you can also calculate tabvles and diagrams fro RK, CSRK, and many other EOS.

With cubic EOS, you cannot have good liquid densities and good virial coefficients; you alway have to sacrifice one for the other. Making b temperature-dependent should be done with caution; it practically always leads to artifacts like isotherm crossing at high pressures, as reported by Trebble and Bishnoi (M. A. Trebble and P. R. Bishnoi, Accuracy and consistency comparisons of ten cubic equations of state for
polar and non-polar compounds, Fluid Phase Equilib. 29 (1986) 465–474).

• How can we apply Rowley equation to calculate thermal conductivity of a multi-component liquid mixture?

Rowley 1982 - (Chem Eng Sci 1982 - 37 -6 - 897-904)

Can equation 6 be applied directly to multi-component mixture if I know the pur component thermal conductivities without using equation 7? If not, how can I apply equation 7?

Maddali V S Murali Krishna · Chaitanya Bharathi Institute of Technology

The following information may be useful for your stkdies

ABSTRACT A local composition model for multicomponent, liquid mixture thermal conductivity has been developed and tested. Only binary equilibrium thermodynamic information is used in the model to obtain local compositions. No mixture thermal conductivity data are required and no adjustable parameters are used. Predictions based on this model agreed, within experimental uncertainty, with the experimental results for eighteen different binary mixtures at 1 atm and various temperatures. An average absolute percent deviation from experiment of 1.0% was obtained over the entire composition range for the eighteen systems. The maximum deviation at any of the tested compositions was 3.5%. Thermal conductivities for ternary systems have also been computed.

A local composition model for multicomponent liquid mixture thermal conductivities

Chemical Engineering Science 37(6):897–904.

Richard  Rowley

www.researchgate.net/.../256140585_A_local_composition_model_for_mu.

How can the reflected waves at the end of a numerical wave tank be absorbed?

I am now working on the establishment of a numerical wave tank. Could anyone give me an overall introduction about the methods to absorb reflected waves?

Liang Sun · University of Bath

What is the mechanism behind the tip splitting in viscous fingering with no heterogeneity present in the system?

What is the mechanism behind the tip splitting in viscous fingering with no heterogeneity present in the system?

J. M. Guevara-Jordan · Central University of Venezuela

Hi, your question is too general. In the context of Hele Shaw Cells the tip splitting  is a function of surface tension, this is a well known result.  Regards

How do you do static and dynamic simulations in Fluent?

I need a quick step by step guide to perform static and dynamic simulation for blood flow in an artery in Fluent. I am a total novice with the software and the topic, and the user's guide is really complicated for me.

David Rathnaraj Jebamani · Sri Ramakrishna Engineering College

Build information
Complete summary of coupling service input file
Analysis details
Participant summaries
Data transfer details
Mapping diagnostics
Time step and iteration summary
Solver field equation convergence summary
Data transfer convergence summary
FLUENT/MAPDL solver output

Try the above steps

• There any previous experimental experience on Impeller designs for Inline Mixers?

There any previous experimental experience on Impeller designs for inline Mixers?

Maddali V S Murali Krishna · Chaitanya Bharathi Institute of Technology

The following information may be useful for your research

Mixing equipment must be designed for mechanical and process operation. Although
mixer design begins with a focus on process requirements, the mechanical
design is essential for successful operation

Ref: Mechanical Design of Mixing Equipment
D. S. DICKEY,  J. B. FASANO
Handbook of Industrial Mixing: Science and Practice, Edited by Edward L. Paul

www.experts.com/.../david_dickey_2_mechanical_design_of_mixing_eq...

How does friction factor depend on roughness?

Hello all,
I would like to seek some clarification regarding smooth and rough pipes and subsequently friction factor relations.

As per the moody diagram we have, that in laminar regime friction factor is only affected by Reynolds number while in turbulent regime, at very high Reynolds number it depends only on relative roughness.

If I am correct till here, then I have confusion regarding smooth and rough pipes. As per one of the criteria where smooth pipes are defined as 0 ≤ u*ε/ν ≤ 5, and rough pipes as u*ε/ν > 70, I would like to clarify the following points.
Say for a given relative roughness, ε, depending on friction velocity u*, the pipe may categorized as rough or smooth pipe. In case I have a laminar flow through rough pipe (i.e. velocity is such that Reynolds number is less but criteria of rough pipes u*ε/ν > 70 is met) , how do I decide the friction factor in such case. Will it be still governed linear relation between f.Re and Re??

In other words, is there any effect of roughness in determining the friction factor in laminar regime? As per my understanding in turbulent regime, the friction factor in both is governed by log law, the difference being term used in log in case of smooth and rough pipes)

Elisabeth Schröder · Karlsruhe Institute of Technology

@Deewakar

The effect of wall roughness in micochannels is discussed controversy.

Experiments in channels of rectangular aspect ratio show that:

"The pressure drop correlations, in both the laminar and the turbulent
regime, agree reasonably well with the theoretical and
empirical correlations found for macroscopic channels."

You can find this statement and the experiments on laminar, transition and turbulent, incompressible flow in following article:

Wolf Wibel & Peter Ehrhard (2009) Experiments on the Laminar/Turbulent Transition of Liquid Flows in
Rectangular Microchannels, Heat Transfer Engineering, 30:1-2, 70-77, DOI: 10.1080/01457630802293449

I attach the article as pfd.