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# Experimental Fluid Mechanics - Science topic

Explore the latest questions and answers in Experimental Fluid Mechanics, and find Experimental Fluid Mechanics experts.

Questions related to Experimental Fluid Mechanics

Hello,

I have a vapor production device that provides me with air+steam flow of 80% or 40% w/w (volume ratio) water vapor quality at 100 degC. The flow passes through a series of valves and tubes where it cools down because of heat transfer. There, the temperature is measured to be something around 50deC. I know that at 50degC, this amount of water vapor corresponds to super-saturated flow. So, I assume that the extra water vapor has been condensed inside the tube, and the resulting flow is a saturated vapor (I don't have access to see how much water has been condensed). Do you find this assumption realistic? Or I may be dealing with a super-saturated flow?

On the other hand, I am a bit uncertain about the measurements of the temperature sensor. To what extent, do you think that latent heat of condensation on the sensor can affect the temperature reading?

The complete flow equations for a third grade flow can be derived from the differential representation of the stress tensor. Has anyone ever obtained any results, experimentally or otherwise, that indicate the space-invariance (constancy) of the velocity gradient, especially for 1D shear flow in the presence of constant wall-suction velocity? Under what conditions were the results obtained?

Multiphase and multi-layer flows such as

**flash floods, shock waves, tsunamis, dam-breaks, etc.**which are more than 3 phases including air, water, and saturated sediment layer, considering different forms (fluid-fluid or fluid-solid mode) with which of the software,**Ansys Fluent****, OpenFOAM, Flow 3D, HEC-RAS, etc.**is better simulated and also which software is easier to understand and more user-friendly?In addition, please introduce helpful s

**ources and links**for self-studying and -learning to run a model with such software.Hi!

Has any study used magnetic bead to be dripped into drop in microfluidics, just as other micro particle? The density (~27g/cm3 for magnetic bead) could be a major problem. How to keep the magnetic bead evenly float in syringe onto pump? Can magnetic bead be encapsulated in drop during dripping? in collection, is the fluorosurfactant strong enough to hold magnetic bead inside, instead of drop cleavage by sedimentation of magnetic bead?

Thanks!

I want to use standard sandpapers of different grit sizes to impart flow resistance to a surface. I am wondering how to convert the roughness of sandpaper to an equivalent sand-grain roughness. Is there any established correlation between grit size and equivalent sand-grain roughness?

I am currently designing a set-up for PIV measurements of turbulent flow statistics in a circular pipe. Different approaches can be found in literature. In my view, the best way is the use of refractive index matching technique to reduce a distortion effect and to get closer to the wall. However, I could not find any paper where flow statistics, such as mean velocity, turbulent fluctuations, dissipation rate etc., are accurately determined in viscous sublayer and buffer zone.

So, can anyone recommend any research paper dedicated to accurate estimation of the flow statistics in the circular pipe for

*y*+<30? I would also appreciate if someone shared some papers dedicated to the dependence of the accuracy of data determined by PIV on pipe radius and refractive index difference between wall material and fluid.Thank you very much in advance and take care of yourself

Dinar

Previously, I have used Reynolds number for dimensionless analysis for optimizing orifice shape ( ). I was hoping to do a similar analysis for more complex geometries. In that, the calculation of Re at the exit surface is tricky due to the curved exit surface (see attached figure).

Re= (ρ∗v∗Dh)/μ = (4∗ρ∗Q)/(μ∗p)

Where, Dh = Hydraulic diameter, v = Mean exit velocity, Q = Flow rate, p = Wetted perimeter.

Would it be more accurate to consider the wetted perimeter of the projected surface rather than a curved surface? (see figure)

We are gonna built an experimental setup about the flow of supercritical CO2 under constant heat flux in stainless steel circular microtube (0.5 mm diameter and 300 mm length). It will be placed lots of T-type thermocouple along the tube to measure the wall and hence the bulk temperature. I would like to take your advice about the correct inserting types of thermocouples on the tube to take the better results. Regards,

Particle Image Velocimetry, or PIV, is a technique for flow visualization and velocity measurement. Also frequently encountered in the literature is 'Large-Scale Particle Image Velocimetry', or LSPIV. What are the conceptual and technical differences between PIV and LSPIV? What kinds of applications are they most suitable for? Do they require the same equipment and procedure?

Trying to find any benchmark on the drag coefficient for a cylinder in axial flow. There are many on the flow from the side, also several on axial flow for Re over 10000. What about the near-Stokesian regime?

Dear researchers,

The following questions are the issues we had when using PIV. We would truly appreciate it if you could help us solve them.

1- Why are velocity vectors highly disorderly shown and recorded with reversed directions or mostly upward directions, and very low values during data collection by rtcontrol software?

2- Although the obstacle on flow path cuts the laser emission coordinates, why are velocity vectors coordinates illustrated continuously rendering the flow crossing path not distinguishable?

3- Why is velocity vector illustrated in the empty space above the flow (with no water), too?

4- What is the best settings for initial pass, overlap, and final window size options?

Best regards,

Maryam

We are looking at some interesting behavior by suspensions in confined thin films. But we're unaware of the basic fluid fundamentals that govern the phenomena of wetting and dewetting of solid substrates. For example, we're searching for simple physical models which can conclude about the role of factors like surface tension, viscosity, and surface wettability. Can anyone suggest some good resources, beyond basic fluid mechanics textbooks, to get us started? Or recent advances in this field?

Hello Everyone !

I am doing validation of a research article . The wind tunnel used in experiment is an open circuit , low turbulence wind tunnel .

I am not sure what boundary conditions should I use in the numerical simulations to accurately validate the wind tunnel experiments .

I'm looking for experimental data about the free surface elevation downstream of a horizontal cylinder in shallow water flow. Ideally for different Froude- and Reynolds numbers in a 2D setting. I'm not interested in the detailed flow structure, only the free surface shape is relevant.

Does anybody know some literature/papers?

For a submerged hydrofoil (Duncan 1981, 1983) such data is available.

Thank you

The speed of the wind is in the range of 1-9m/s and we are targeting an area of 3 by 3 cm or even smaller, say 1cm by 1cm. I was thinking about using a continuous 532nm laser with a high speed camera for that. People employed pulsed laser up to 5kHz as the light source, but the frame rate when capturing the image is set as 1kHz. I'm thinking if it gonna work if I use a 1kHz frame camera with a continuous laser. The seeding particles I'm thinking are atomized olive oil.

Hello all, currently I am doing experiments, in these experiments I am using a nozzle in order to cool a hot surface, meanwhile I am changing the water flow rate, and what I noticed is, when I change the water flow rate, the cone angle changes, and I am wondering whether the quality of the nozzle is low, or the water flow rate may affect the cone angle of the nozzle! Any answer will be very appreciated. thanks in advance for you all... :)

there is some papers that worked on reynolds number (lower and upper limit) for which darcy law can work. is there any upper limit reynolds number in forchheimer equation?

Hi everyone. I would like to ask fro suggestion about transferring cells out from a microfluidic device.

My work is to form cell spheroid inside the microcavity channel. Then, I will transfer them out from the device, but we get less cell spheroids as we did in the device.

Conditions in the experiment:

1. Cavity channel - 3 x 3 mm, channel height 100 micron

Note: We cannot change the height of the channel due to some limitations in forming spheroid.

2. Inlet and outlet size is 1.0 mm outer diameter

3. Coat the device with 10%BSA before loading cells for preventing cell adhesion

4. Inlet is connected with syringe + PBS / Outlet is connected with pipette tips

In our conclusion about the cause of this problem,

1. Cells may be exposed to high shear stress in the abrupt direction change from horizontal to vertical channel which causes spheroid to be broken. So we get less spheroid resulting from cell breakage

2. Or I see some cells get stuck to inside the channel near the outlet via a microscope even though we try to flush them out. so we get less spheroid originating from cell stuck in a device.

Does anyone deal with this problem before?

Thank you for your comment in advance.

I work on the flow of a gas in a micro channel, the goal is to compare between the analytical solution and the digital one for the temperature fields, the problem is that analytically I have that the difference in temperature Between the wall and the gas

CD is the ratio of actual flow rate to the theoretical flow rate

So, how can we calculate the theoretical flow rate?

To work out the aerodynamics of vertical axis wind turbine (VAWT) and probably the HAWT, we need to know Reynold number (Re) to use it along with angle of attach to find the drag and lift coefficients (C

_{d}& C_{l}) from the airfoil characteristics,**I would like to know which velocity we use to find Reynold number, Re=v*L/neu,***is it the induced (axial flow) velocity (assuming that MST or DMST is considered), or the relative velocity, or the tangential velocity V*_{t}*=Omega*R?*I have met a problem in measuring boundary layer by using hot-wire and sincerely ask for advice: There always exist low frequency disturbacnes ( around 10hz~20hz) when the probe intrude into the boundary layer (the frequency varies a little with change of traverse system ). When the probe is fixed on the plate, there is no this low frequency disturbance. (with Freestream velocity of 8m/s, its turbulent intensity is below 0.15%. In the experiment set-up, the probe used is TSI 1218-T1.5, and traverse rod with elliptic section (a=4mm, b=8mm) is inserted through wind tunnel side wall ) .

What is the most probably factor that causing this low frequency disturbance and how to avoid it? It is suspected that traverse system may be the cause of this problem, then what is the best set-up for traverse system? Thank you very much!

Normally, we will use pressure drop to calculate the pressure in a pipeline.

Can Bernoulli's principle combine with pressure drop along the pipe in calculating the pressure of the fluid?

What is the condition needed to use Bernoulli's principle? Instead of incompressible fluid, inviscid region of flow* steady flow?

Is the pressure drop formula, like Darcy–Weisbach equation derived from Bernoulli's principle?

Appreciate if someone can answer my question. Thank you.

I am trying to determine surface roughness of a curved surface of 100 micron length. I wish to segregate it into five equal parts and then determine the surface roughness of each part. The surface roughness should be of the order of <=1 um. As per theory, the cut-off length should be minimum 0.08 mm. However, the sample is not that large enough. What should be the proper way for measuring surface roughness in such case?

I am trying to build several cases for solver and CAA-library code validation. There are breathing, trembling sphere, baffled piston.

In all cases we can see phase difference between pressure signals. I'm explaining it by inertia like in the mass-spring system. Is it correct?

How can i modify wave equation results or my CFD solution to clear it from such kind of discrepancy? I need to clear it because i'm trying to validate very different solvers (for example with mesh motion) and already observe reflections from boundaries (so then i will need to test some types of non-reflecting) and i suppose that this phase difference could make further analysis harder.

Thank you for any help ("to read" recommendations are also appreciated).

Last figure just for reference (baffled piston, 2d-axissymmetric case).

Due to the alternating vortex wake (“Karman street”) the

oscillations in lift force occur at the vortex shedding frequency

and oscillations in drag force occur at twice the vortex

shedding frequency. Why is that?

I have read of lasers used to measure flex in a kayak paddle, but wonder if water displacement is more important than an indirect measure. But how can it be done on a lab and in the ocean?

As it is known if pressure drop between inlet and outlet of a geometry is known friction factor can be calculated from equation below;

Dp = f (L\D) (ro U

^{2}\2)But use of this equation is only possible for fully developed flow. There are some other correlations to for pipes and square ducts but I need friction factor for wavy channel. Is it impossible to find it by measuring only two pressure value?

Please suggest any books or materials for reference.

Hi,

I'm studying the turbulent flow past an elliptic cylinder at different angle of attacks.

What reference area should be given to FLUENT for lift and drag coefficients?

Should it be varying with the angle of attack?

What should be the characteristic length for calculating Reynolds number? Should this also vary with the angle of attack?

Thanks.

In flow analysis for rough pipe using Large Eddy Simulation, how the roughness height and roughness constant value can be incorporated. Is it possible?....

Hi,

I am trying to employ stereoscopic PIV in a large flume which is 15-m long, 1.2-m wide and 0.6-m wide. I am looking for a local seeding technique in order to control the concentration of tracer particles in the object plane. Currently, I am using two spray pump installed about 3-m upstream. Are you aware of any other techniques?

Thanks,

Nasser

Hi,

i am simulating flow past a rotaionally oscillating cylinder. i've read some papers related to this and found that some authors were taking Re based on the perimeter and some based on the

*sqrt(a.b)*(a,b- half of major and minor axes).Mean position of the cylinder is going to be the major axis which is perpendicular to the flow.

Thanks.

I want to use vortex mixer that has temperature control when I am coating iron oxide nanoparticle with DMSA(dimercapto succinic acid).

But it is difficult for me to find vortex mixer "with temperature control".

Is there anyone who can recommand this vortex mixer model?

reference is here:

Colloids and Surfaces A: Physicochem. Eng. Aspects 316 (2008) 210–216

A flow between concentric cylinders is called Taylor Couette flow. A matrial having pores (void space) is called porous material.

I've found some references that use 2200 to 2300 xg for 30 minutes? But then I've found some people on here asking about cell fractionation that have been recommended that 500xg is the max they should use. Is 2200xg overkill? Does 500xg just apply to separation and not packing of RBC?

Any help would be greatly appreciated.

Alan

Hello! Does anyone know about speed flying from a Taylor cone of droplets? How to calculate it? We use horizontal electrospinning.

In solving the momentum equation which is more realistic BC's, mass flow rate or pressure drop. How can we justify mass flow boundary condition for BWR and SCWR? Is there any reactor practically working on controlled mass flow rate or something like that?

Any help is greatly appreciated. Thanks

Dear,

I am trying to use Salome recently, first with a simple geometry, as attached.

But after I used the partition tool, there are some internal faces, which are not expected at all, as highlighted in the attachment.

Could any body show me how to remove the internal faces please?

Thank you in advance.

Yours Sincerely,

Bill

Well, I feel so confused about calculate camber on glulam.

Is it determined by radius or span or else?

Does anyone here have some formula to calculate it?

Thank you anyway.

There appears to be an aerodynamic instability of 3-wire conductors in overhead power lines.

Hi, I want to plot dean vortices inside a 90 degree pipe bend at different section (30 degree, 60 degree etc.). The pipe bend axis rotates from x-axis to y-axis from 0 to 90 degree. I have already plotted vortices at bend outlet (90 degree) and in the downstream region by using vector plot and streamtraces option available in tecplot of x-velocity and z-velocity. But what will be the vector variables for plotting that inside 30 degree of bend section as the bend rotates about z-axis, i.e from x-axis to y-axis? Should I have to create new variables of velocity components? Hope my problem is clear to all.

Water is flowing over a flat inclined plate and I have to cool the plate to freeze the water. How should I decide the geometry of the plate ?

Dears

I have a question regarding the time derivative of pressure in low-Mach number approximation of NS equations. Referring to the work " Numerical study of a channel

flow with variable properties" done by Nicoud, depending on the whether the simulation system is closed or open, the time derivative of pressure can be defined as ... (see the equation 8 of his paper) for the closed system or zero for the open system.

Could somebody tell me why for an open system this is zero?

Thank you all

I want to design steam jet refrigeration system and i am facing deficity in design super sonic CD nozzle. can anyone give some guidance about how to start design designing for particular pressure difference?

One way for this that I came across in literature was to represent the data in terms of irrotational and divergence free component and subsequently solving a poisson equation for the divergence-free part. Numerical solution for which is not coming correct maybe due to smaller window.

Microchannel experiment, Polymer flow

For external flow over a flat plate, what is the reason that boundary layer thickness is continuously increasing. What physics is responsible for this ?

I found the vortex type generated by pitched blade or hydrofoils agitators but all the times there are oriented to push the fluid down and in clockwise flow. But if i have a blade that is oriented to push the fluid up i am not able to guess if the vortex will be oriented upwards or how. I attach a view of my complex agitator and i am talking about the vortex created by the outer blades. Thanks in advance!

Dear Researchers and Professors,

I dispersed 0.5 gms of MgO in a litre of DI water and sonicated it for 3 hours and found that, it did not disperse well. After keeping it idle for a day, found that it got agglomerated.

I did the same procedure for CuO in DI water. Got dispersed partially, but settled after 8 hrs.

Can anyone please suggest the optimized volume or weight fraction and surfactants and/or dispersants to have stable Mgo and CuO based nanofluids with DI water as base fluid?

Dear All,

I am calculating lift (Cl) and drag coefficients (Cd) for a rotating airfoil. Let's say the tip speed ratio (TSR) is equal to 2 and the wind speed is 8m/s. I noticed that due to rotational motion, the airfoil will see an additional velocity tangential to the airfoil body, therefore Cl and Cd should be calculated based on the relative velocity (Vr).

However, when I did this, Cl and Cd were not comparable with the aerodynamic polar in static conditions. Since the dynamic stall (DS) should occur, the lift is expected to increase, and this was not observed when I used (Vr) as reference. Cl was significantly reduced compared to the static polar. Nevertheless, this was not the case when the wind speed was used as the reference. Cl was increased and behaved as usual DS characteristics. Please see the attached picture.

As a note, DS characteristics such as the leading edge vortex creation and convection were clearly observed. So, I am sure that DS is occurring.

Can somebody suggest me an idea? Thanks in advance for your response!

Galih

When a pump is tested in air, fluid leakages are entering inside the pump through the gap betwen the impeller and the diffuser for some flowrates. These fluid leakages can significally modify the flow inside the diffuser.

In order to understand the behaviour of 3D compressible unsteady flow we use URANS. Output processing of particle paths is very valuable, particularly if we include the thermodynamic variables for the particles at each time step. But I know the energy does not simply convect with the mass particles. It can travel 'sideways' by diffusion of heat and also by frictional transfer of work between particles.

I would be obliged if someone knows good lecture to this topic. In my case, I'have to focus on a compression shock in shock tube from round to square geometry.

I'm glad for every source of information.

Sincerely yours

Hello everyone,

I am recently working on experimental analysis of intermittent type two-phase air-water horizontal pipe flow. In this regards, i want to eagerly know the dynamics of intermittent flow structures (mainly governing forces or force balance inside the slug or plug type intermittent flow). Can anybody suggest me the literature which includes the free body diagram with considering all forces inside the slug or plug body?

how to reduce drag on ships by lubrication of air?

I have been researching the air flow effects on frost formation at fin and tube heat exchanger and I need uniform flow media in front of heat exchanger. However, I haven't ensured at my tunnel illustrated attached image due the fact that it doesn't a contaction section including honeycomb or screen. I would like to thankful if you share documentation regarding contraction design at low-speed wind tunnel (my velocities are max. 5 m/s) and your recommendations. Also, Is there another method to form more uniform flow at entrance? Thanks and regards.

Hi Dear Colleagues,

As you know, refrigerant two phase distribution at evaporator is big problem because of the fact that it can cause significant capacity reduction unless used optimum distributor. Thus, I am planning a experimental test rig but I'll use water- vapor mixture as refrigerant, merging this mixture at determined ratios and measuring the flow rate at outlet of each circuit. Does using water instead of refrigerant such as R404A give certain result? I would like to take your value opinions. Thanks

I am wondering if velocity in formula means average velocity of fluid passing through cavitator, or velocity of fluid within the cavitator, between points with different pressure?

I'm trying to reconstruct the density distribution of an atomic gas jet from measured projections. I want to compare my results with what is expected from jets' distributions. I found an article which shows jet density profiles for Laval and conical nozzles, but this article discusses jets with clustering. I wanted to know if I can rely of these profiles even in the case with no clustering ?

I'd appreciate if you can refer me to a scientific source backing the answer.

By the way, if you also know of good articles which discuss the density profiles of gas jets (with and without perturbations in the nozzle), I'd also appreciate if you can refer me to them.

As stated in the literature, in species transport model mixture formulation, the components are mixed at molecular level and velocity and temperature are the same for all components.

Given the case for non-reactive mixture and the simulations I carried out, the mass fraction data is available for different components at various axial locations inside a cylindrical channel.

However, I intend to know how the species transport model can be used to know the extent of mixing between the two gases.

Secondly, since there is no reaction, what is the factor that is causing the mass fraction change?

I have simulation results for a particular problem (say 1D advection equation) for two grids. One is a coarse grid while the other is refined. I wish to determine the error scaling with time between the two grids theoretically (using pen and paper). Can I do this?

I'm considering heating and vacuuming a solution to decrease dissolved gases as well as coating with a superhydrophobic material. Any ideas?

Hi,

I want to carry out DNS of a high-speed turbulent reacting flow. How can I properly determine the Kolmogorov length scale according to the basic flow parameters such as velocity, temperature, pressure, etc. Or how can I determine the required grid resolution?

Hi,

I want to actually model a vortex tube in CFD. To do the meshing part I am using ICEM CFD. So I actually need to block the inlet region in it. I have trying various to achieve this but my attempts to do were a complete waste as i had a very bad mesh. I want to know how to actually block that in order to have a good mesh. Please reply as soon as possible.

attached are the model files i have made in ICEM

Thank you,

Regards,

Sankeerth

Thank you

How can we take into account seagrass (posidonia) and bed rocks rougness in the MIKE 21/3 coupled Model FM?

I applied FFT to my hotwire data downstream of a circular cylinder to find the vortex shedding frequency, however two clear peaks appear in my final results. How can I say which one is the actual vortex shedding? what could be the other one for?

Hi, recently I am focusing on developing a new way to measure the size of drops adhered to solid. So I need to create different sizes of drops at first, and the more uniform the drops, the better.

Is there anyone that has some knowledge about this?

Is there any relation for calculation of x(in the picture)?

I have to connect a syringe to a squared glass microcapillary. I looked in many online shops but I've never found a proper fitting thus having always liquid leakage between the microcapillary and the connection.

I am using a plunger pump to generate a 20 l/min of high pressure water flow rate to be injected through a nozzle. In order to avoid propagation of disturbances and provide smoother operation, a buffer tank is installed between the pump and the nozzle. The problem I'm facing now is that the flow rate after the buffer tank is reduced to approximately 8 l/min. Is there any explana for this? And is it possible to keep the flow rate constant (20 l/min)? If yes, how?

Thank you in advance.

I want to know whether we can use Bernoulli's equation in the case of pressurized (above 5 bar) pipelines of gasoline.

I work on polymer gels. The yield stress is ~100 Pa. Below 100 Pa, both G' and G'' show plateau wrt stress. But the G'' plateau fluctuates from run to run while G' does not. Can anyone explain this? Thanks in advance :)