Wind Tunnel Testing - Science method

why don't you check with blockage corrections in automotive wind tunnel? The blockage problem should not be reduced to the jet expansion effect alone. There is a nozzle effect, a collector effect and a static pressure gradient effect of the empty test section as well (see SAE Technical Paper Series).

The answer is that the similitude is governed by the non-dimensional numbers. You can scale the dimensions but you have to increase the velocity in the wind tunnel in such a way to get the same Re number. A further parameter, the Mach number can be required. Clearly the fluid must be the same to have the same viscosity.

Manoj Pradhan please find your answer in the link attached

You can do non-linear analysis if you want, but it totally depends on your aims. According to some CODEs, you can do linear analysis for up to 50 story buildings.

Thus, specify the purpose of the design and refer to the restrictions of your country's CODEs.

Dear Prasenjit Sanyal

Try this book https://books.google.com.ua/books?hl=ru&lr=&id=nUHWDwAAQBAJ&oi=fnd&pg=PR11&dq=wind+tunnel&ots=LwHmhX27Xx&sig=FoSoHM6daPPoys2R92pMnkpecQw&redir_esc=y#v=onepage&q=wind%20tunnel&f=false

Barlow, Jewel B., William H. Rae, and Alan Pope. Low-speed wind tunnel testing. John Wiley & Sons, 1999.

Regards

I would suggest to check if you have an scaling factor enabled in the software.

Thank you very much

Khaled. Yes, the buildings and structures you mention (and many other human constructions) are routinely studied in wind tunnels every day. Some at universities (eg UWO, CSU, TTU, UF, Monash, HKUST, etc.) and some at commercial facilities (eg RWDI, CPP, MEL, etc.). The success at modeling various actions on a small-scale model in the wind tunnel has been well-established and refined since the 1960s. There are dozens of wind-engineering societies and associations in many countries around the world (AAWE and AWES to name two I belong to) and these are all connected to the international body, IAWE. The best assessment of "accuracy" is to compare the wind tunnel with a full-scale building in the real wind. There are several good examples of this (a well-known recent example was the Texas Tech University Building that spanned work over the 1990s and 2000s, and an earlier effort in Britain called SILSOE) in the literature and, with some caveats, the agreement is really quite good between model and full scale data. The Elsevier journal called Journal of Wind Engineering and Industrial Aerodynamics has been the source of many papers in this field for over 40 years. Lots of reading for you!

Hi,

To create an interface, you need to do two steps; one in the design modeler and the other in Fluent itself. There may be different ways. For simplicity, consider you have two blocks one over the other and you need to define the interface between them. You will need to define each block as a domain so as they appear in Fluent/cell zone conditions as two domains. Then the common surface now will be two coincide surfaces. Then, you name each boundary, e.g. int and int1 even as walls.

In fluent, you will change the boundary type to interfaces from the boundary condition. Hence a new tab in Fluent appears called mesh interfaces. You will need to create the interface in this tab. That is easy by create/edit and give a name for a new interface. Then, specify the boundaries "int" and "int1" in the columns on the middle and right, just one boundary in each column, for example int in the middle and int1 in the right.

Hope that helps

following

Hi Mohamed Azab I can open the second one.

Thank you

Regards

Soma

Dear @Shobhan Roy,

1. > first determining bl thickness (delta) and integrating for y=0 to delta

correct;

2. using local value of velocity instead of inflow value is the only and absolutely correct way. When dealing with a flat plate these values are almost the same. It is the reason of this little mess.

I'd suggest to plot all evaluated quantities (for example delta*) as functions of x and double inspect any ambiguous regions. If you are unsure whether your algorithm is correct in some regions (for example, shock impridgements on boundary layer), then just plot velocity(y) profile and determine delta by an eye instead of algorithm.

Best regards.

The most sensitive of the Microswitch pressure transducers (sealed, plastic, robust device about 50x25x12 mm in size with two pressure ports) are inexpensive and at very linear in the calibration in terms of Pa/V. From memory around 100 Pa/v when you calibrate with screw-driven syringe, or similar. Good luck. LC.

agree with@ Dominik Felix Finger

regards

You might try making the same series of flow measurements at sections across the tunnel but at a series of positions farther and farther upwind, so you can observe if this 'bump' in your transverse cross section profile is growing, shriking, or constant as you move upstream

Do you have a contraction at the inlet to your tunnel, and honeycomb or simmilar t provide something like smooth uniform flow entering the tunnel? Also - are the inlet and exit to your tunnel far from any walls or columns and free from blockage (no crates or desks or anything to obstruct flow coming in or exiting)?

Similar to first suggestion - you might try measuring the wind speed in the tunnel on a crossectional plane near the beginning of your test section, to see if there are some anommalies in the flow to begin with, or if they are creeping in as the flow moves down the test section.

Could you expand your question with the details of your problem? Why are you working with LES in such a problem?

Hi,

your WT-Model should be adapted for one Mass-flow at one condition. If your are interested in the drag at a cruise condition for example, perfom the WT-Tests at that specific reynolds number, and further there should be some comparative calculations for the other test conditions, which are preferably done by CFD. In this way, you must always account for the corrections starting from the most likely test condition you are performing. Another way, would be to have two or 3 different configurations for your WT-test.

Best Regards!

Thanks so much for the answers, we will carry the model tests after the computer simulation study.

Thank You very much.

Wind tunnel testing will be used as a calibration tool for cad.

Sometimes when there are limitations on the accuracy of the testing conditions like you wouldn't like to invest in a moving belt beneath  the car you can run the cad with the same boundary conditions and than extend to the real boundary conditions 

can u look this file

Thanks Martin George Rose

However, our problems are we have the experiment data sets of 20% scale model at several different Rey. numbers. We need to do the extrapolate to free flight condition. But I am not sure about the method that we used to extrapolate the maximum lift from WT

yes sry 

lamda= (omega*R)/wind speed =(7.54*5.029)/25= 1.52

Also I accept the fact that 3d corrections has to be included, I have included various corrections by Snel, Lidenburg etc. But my concern is about CFD and experimental analysis.

Sreejith,

If all you need is an estimate of power and torque, then you can take your subscale results and scale them up using historical trends (in changes of lift to drag ratio from low Re to higher Re) to inform expected changes in maximum lift to drag ratio.  This will get you to a decent ballpark estimate.

For the second part of the study, anything you conclude from your parametric study will be specific to the Low Re regime in which the test is performed and will not translate to the higher Re application.

In addition, the CFD gets trickier at low Re since the performance is so conditional on where and under what conditions boundary layers separate.  And just because you can validate your code at low Re's doesn't mean it will work well at the higher Re's of the practical application........

If I've been found out correctly you need to determine outlet conditions of air side leaving a fan with a particular geometry.

It is recommended to use HTRI air cooler design / rating sophisticated program to obtain wanted data

Yes, sir i am working on influence of wind also

I would suggest testing different NACA two or four digits airfoil series. You can find available experimental data to compare with at different Reynolds number values which would definitly fit in your wind tunnel specs. You can compliment the experiments with many videos on Youtube that explani the numerous applications of airfoils. As an excercise, you could ask thge students to do slight changes on the airfoil profiles, and observe the effect of such changes in Cd and Cl.

About portable wind tunnels, you may refer to Prof. Mario Carbonaro of von Karman Institute for Fluid Dynamics at:

Perhaps should you record data during a reference test point without wind, and make your analysis of data-with-wind relatively to it ? However, the variation of atmospheric pressure you mentioned is quite low...

Even if it is not too late, adjusting the speed of the airflow to keep the total pressure constant has a disadvantage: if you study a wing airfoil, your dynamic pressure will change, thus the pressure distribution will change, like the supersonic plateau, the shock location, especially in the transonic domain...

Fatigue in the resonant frequency to minimize the amount of energy needed to carry them out and reduce the duration of these tests.

You will need to select the appropriate parameters of the experiment. Particularly important is the power of the excitation signal. If it is too large the can achieve load causing plastic deformation in a very short period of time.

To my knowledge and experience, you may perform some studies such as: 1) Particle deposition in fully turbulent airflow; 2) Particle resuspension from wall surfaces under the effect of fully turbulent airflow. These are two issues related to the indoor air quality problems. I attached three of my previous publications for your references, but I found there are still problems, which need further study, especially the experimental work under wind tunnels.

Dear Milad,

I think you misunderstood my question..."parked situation" or "parked codition" or "standstill" refers to the situation in which the turbine is not rotating.

Anyhow, thanks for your consideration about my problem dude.

Laurent is right, you can use FAST and AeroDyn. They are well-known, well-accepted codes, applied successfully in many previous investigations. Also, FAST and AeroDyn are freeware (open access software), and it is possible to periodically download improvements of these tools. You can also use QBlade, which I explain in the last paragraph.

These coupled software tools were developed by the National Renewable Energy Laboratory (NREL) for aeroelastic simulation of horizontal-axis wind turbines (HAWT): FAST is a dynamics analysis code, and AeroDyn is an aerodynamics analysis routine capable of interfacing with FAST. In particular, the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code “is a comprehensive aeroelastic simulator capable of predicting both the extreme and fatigue loads of two- and three-bladed HAWT”. AeroDyn is an element-level wind-turbine aerodynamics analysis routine that, when used in conjunction with dynamics software (e.g., FAST, YawDyn or SymDyn wind turbine dynamics analysis codes, or ADAMS® commercial dynamics analysis package), allows computing the aerodynamic loads on the blade elements of HAWT. For this purpose, AeroDyn uses essentially two wake models: the blade element momentum (BEM) theory, and the generalized dynamic-wake theory, a model for skewed and unsteady wake dynamics. Both models are used basically to calculate the axial induced velocities from the wake in the rotor plane, taking into account the influence of tip losses, hub losses and skewed wakes. AeroDyn uses also a dynamic stall model based on the semi-empirical Beddoes-Leishman model, and a tower shadow model based on potential flow around a cylinder and an expanding wake. Since FAST and AeroDyn incorporate models of controller (servo) dynamics and structural (elastic) dynamics, they enable also simulation of the behavior of the control and protection systems and the structural dynamics. It is worth to note that FAST and ADAMS®, together with AeroDyn, were evaluated in 2005 by Germanischer Lloyd WindEnergie and found adequate for computation of loading of onshore wind turbines for design and certification.

These tools require several input files containing diverse data like, for example, the wind-inflow conditions, and physical and aerodynamics parameters of the wind turbine blades. The first step is thus to characterize the wind turbine selected for your study and to build the input files requested by FAST and AeroDyn. You can do that using the information and technical data provided by the manufacturers, and data measured from the physical components.

QBlade is open source software for design and simulation of HAWT, distributed under the GNU General Public License. Its integration in XFOIL allows airfoil design and airfoil performance analysis. QBlade allows also for extrapolation of airfoil performance data to 360° angle of attack, turbine blade design, and realization of BEM simulations of the rotor and turbine. Finally, this tool allows structural blade design, modal and static loading analyses using QFem solver, generation of turbulent windfields, and realization of FAST simulations. You can download it here:

Hello Ahmed.

If you look at the rosettes, these are primarily used for measuring dual (or multi-axis) strains. It is actually  a combination of commonly used strain gauges usually arranged in X-Y (90 degrees) orientation to determine the stress/strain in these two (or more) directions.

I would suggest to go for a Torsional gauge (or torsion strain gauges) which has some slanted pattern (unlike linear patterns in the commonly used strain gauges) for your applications. I believe you want to study or measure the bending of a the blade if it is rotated (bent, not the actual rotation) due to wind pressure.

Hope this will be useful to you. Best luck!

It depends on what you are trying to determine and what assumptions you make.  Typically root bending and torsion moments versus tip bending and angular deflection are presented.  Sometimes the in-plane (lead/lag) bending moment with in-plane tip deflection may also be useful. 

After researching on the experimental methods to get the COG and to make the question useful for those who search in this point:

Method 1:

The center of gravity of the blade can be found out by hanging the blade as free as possible in two or three different positions and marking each time the vertical line that starts from the pivot point and the intersection of the vertical lines gives the center of gravity as shown in figure.

Method 2:

Mounting the blade on two jigs, each one at each end. One of the jigs will be displaced along the blade therefore the distance between the two jigs changes. When the movable jig is positioned beyond the center of gravity of the blade, then the blade becomes unbalanced and starts to turn. 

Hope this help all colleagues who answered me. 

Thanks Gerro Prinsloo and S. Tolun 

Just a comment. condensation in blow down tunnel is dependent on many factors like moisture content, air quality, length of channels.  Its not an instantaneous phenomenon.

Hi, Wood!

Yes, it's difficult task. One possible resolution is as follows: In most cases, flow sensitivity to the Reynolds number decreases with the increase of Reynolds number. For example, the non-dimensional vortex shedding frequency behind a prism becomes less sensitive to the Reynolds number at higher Re. You can find the same thing in the Moody chart for pipe flows. So, do the experiments in your wind tunnel at some different Reynolds numbers available, and guess the solution at the desired Reynolds number by extrapolating results obtained at lower Re numbers. Clearly, this approach will introduce error, and the result may be either good, fair, or bad. I think that you can evaluate the quality by running the Fluent code at lower Re's. As you know, engineering is always with errors. Obtaining solution by a rule-of-thumb is always better than doing nothing. Regards, Ji Ryong.

Are you using the same flow profile (measured in the wind tunnel) for your CFD inlet conditions?

I fully agree with Francesco! Static tests are entering the realm of structural design. As for the use of quasi-2D stationary wind tunnel measurements for the design of rotating blades operating under extreme turbulence and gusts....well that is another huge discussion :D

THe 5% physical scale is generally, to avoid too much error. Actually any cross section blockage (CSA model/CSA tunnel) of up to 10%, would allow corrections which are regarded as accurate. Anything above 10% would mean corrections to the results could be difficult to justify - meaning whatever readings you have cannot be guaranteed of their correctness, especially if you want to measure velocity and pressure.

It will depend on the goal of your experimental investigation. If your aim is to mimic 'homogeneous' decaying turbulence you may find it will only be realised much farther  from the grid than the standard rule of thumb of 30M (where M is the mesh size), or perhaps it will never really homogenise because it will persist as a wake-like flow . (Btw, you may want to refer to the book chapter by Corrsin who effectively put forth these rules of thumb [S. Corrsin. Handbook der Physik, volume 8, pages 524–590. Springer, New York, 1963.]). In essence it will depend how small the grid is compared to your wind tunnel. If it is too small it will be closer to a porous plate than to grid-generated turbulence. In case it may help, here follow references to experiments in flows closer to being wake-like flow with bleed air such as fractal spoilers [Nedić et al 2012, AIAA Journal, 50(12), doi: 10.2514/1.J051387] and fences [Keylock et al 2012, Environmental Fluid Mechanics, 12, pp 227-250]. 

Hello,

I am not sure that your results are absurd as you said... Since your measurements are made in the very near field of the jet (sometimes referred to as the production region), it is not surprising to observe the energy dissipation rate increasing in this particular region of the flow. A careful analysis of figs 7 to 9 of Mi et al, MST 2011 reveals that epsilon increases from 5D to 7D and then starts decaying.  Consequently, the Taylor and Kolmogorov length scales decrease before increasing beyond 7D (see figs 8(b) and 9).

Did you try to compare your results to that of Mi et al (Meas. Sci. Technol 2011), the latter being in the range 5 \leq x/D \leq 30. The measurements of Mi et al in the round jet were carried out at a Reynolds number of 20100, I hope you made yours at a similar Reynolds number. Otherwise, have a look to the following publication by the same authors (http://dx.doi.org/10.1063/1.4811403), even though the range of x/D is slightly larger (>10D).

Note also that, independently of the electronic noise contamination, the relevance of your measurements depends on the validity of the local isotropy hypothesis as I guess that you use the 1D surrogate of epsilon (\epsilon = 15 \nu (du_dx)^2), or perhaps a more sophisticated surrogate. Anyway, this hypothesis is unlikely to apply in the near field.

Finally, apart from the hypothesis of local isotropy, the ratio L/\eta (L being the length of the hot wire) may be also critical for a reliable estimate of epsilon to be inferred...

The best would be to compare your results to a DNS. I am not sure but perhaps BJ Boersma reported some profiles of epsilon in the near field of a round jet ...

Good luck

Fabien

Hi,

I'm not sure if you are asking about the information of 3D reconstruction using photogrammetry for buildings or aerocrafts. I guess what you need is the 3D models for wind tunnel testing, and in that case, you can have some reviews about the topics of 3D construction, close-range photogrammetry, and maybe Laser-scanning. This will help you building a frame about basic theory of photogrammetry. Also you can practice and model your overlapping photographs with some professional software like Photomodeler for close-range photogrammetry and Cyclone for point cloud processing.

Hope this helps.

The integral length scale is a challenging parameter to maintain. That is turbulence is not jus intensity. The whole spectrum is important unless you are interested in mean values of loading.