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Hi. Does anyone have any references to how a diffusor should be designed, i.e. angles vs. velocity. My "diffusor problem" has air as fluid and an inlet/outlet velocity approx. 20m/s - 5m/s. I would like to avoid any detachment. And, does anyone know if a diffusor flow is inherently unsteady...

1) You need to sample fast enough to capture the flow changes you are looking for, ie. see to that you have enough measuring points to draw up a profile that is smooth. Only you know what you are looking for (how fast the gusts are changing measuring values from the steady state, etc.) 2) Maybe...

Hi. I want to make an analysis of a device to find its eigenfrequency. But I am not sure how to do it. I seem to remember something about an FFT analysis of the frequency recorded, but that’s it. If anyone could help me with direct informations, I would be most grateful. Links are also...

When making a frequency measurement, one has to make sure that the Nyquist criterion is obeyed. But what if I have no frequency filtered data. Is it correct to make a FFT transformation and just look at the first half of the transformation? Is that the same as a low pass filtering?

Hi. I have a duct with a 90° bend. After the bend I want to have a symmetric velocity profile. But if I do nothing to the flow, the velocity distribution will be skew. What can one do to even out the distribution? And how far from the bend will the skewness remain? Flow details: u=10m/s...

Hi Johnchance. The tunnel is an open pass-through, i.e. I need the drive section to be upstream of the test section. I want to have a mixing chamber where the moisture and heat can be distributed uniformly before it enters the plenum (where the flow is straightened). He he. Well. I guess that...

amorrison4: Thanks. I have done that now. ccfowler: Thank you for you comments. My answer: I am not concerned primarily about measuring velocity at near zero. Velocities ranging from near zero to 40m/s are my first targets, but velocities from near zero to 350m/s are needed. And why? Well...

Hi. I want to build a wind tunnel for calibration of hotwire, pitot tubes etc. I have made the following considerations: A large plenum where the velocity will be nearly zero (to measure the static pressure as upstream condition for outlet velocity calculation). A baffle plate at the plenum...

Hi. I want to build a wind tunnel for calibration of hotwire, pitot tubes etc. I have made the following considerations: A large plenum where the velocity will be nearly zero. A baffle plate at the plenum inlet. A honeycomb, screen or a similar device inserted for to ensure a flat velocity...

Hmmm. I do not have any experimental data available. I was wondering how to estimate the turbulent velocities from a given intensity. The turbulent velocity in the formula calculating the intensity is a mean square. Is there any way of breaking this mean value to its (estimated) pieces...

Hi all. How can I determine the maximum velocity (the fluctuating turbulent part) in a flow that I estimate to have a turbulence intensity of 50% ? I cannot see by looking at the definition of the intensity how I with the intensity and a mean velocity can calculate the fluctuating...

MVD commented that the additive seems to reduce the turbulence. I am not sure, but it seems to me that turbulence is not reduced. It must be reduction of the shear stress through reduction of viscosity?! The reason I do not believe that the turbulence is reduced is because a high turbulence...

I agree. I would say that the car. length should be the 1ft. And the Cd value sounds fine to me (but then again, I have not worked with drag calc. in a long time).

Hi Can anyone help me with references to standards regarding pitot measurements and design ? I know of two ISO standards (3966 and 7194) but they may be too old and there may be others. I have tried a search on ISO´s and EU´s standard homepages, but found no useful information.

Thanks everybody for your answers. A observation: I just tried to hook a pressure transmitter up to a small system, and I noticed that when I held my hand around (just around, not bending, shaking or anything else) and heated the small plastic tube, the absolute pressure rose from 50mmWG to...

Hi. What is the best way to measure velocity approx 5m/s +- 0.1m/s in air approx 50C ? A pitot tube would have to measure a difference of 0.005Pa to detect a 0.1 m/s change, and that is properbly impossible. I think that a hotwire tool is the best solution, but I am not sure. Any comments on...

Thanks. I will take a closer look into that. Do you know if it is possible to say which frequency is “the most” responsible for the dispersion (of e.g. dust) in a flow? Is it the largest eddies, the smaller but more energy containing eddies or the smallest eddies (those responsible for viscous...

Well. I know that my question is not well posed, and I am not even sure that I know what I am looking for. Let me try to describe my search. I am looking for at way to calculate the frequencies of the eddies in the flow. Naturally I need to know the sizes and numbers of these eddies to know the...

Hi and thanks. I am not sure if I understand your answer correctly, but you are talking about the wake frequencies after a bluff body, right? There is no bluff body in the flow. I am trying to understand the frequency dependence in a tube and right after the tube. No bluff body in the flow. If...

Thanks. Do you know what happens in the boundary layer? And do you know why the laminar flow is dependent in the first order? (and why the turbulent in the second order?). And, as I have understood it, the reason of using dimples in the golf ball is because this introduces/insures turbulent...