Norbert Szaszák Ph.D. student,
University of Miskolc, Department of Fluid and Heat Engineering
2013.
Tavaszi Szél Konferencia 2013, Sopron
Outline
Doctoral topic: laboratory investigation and development of novel turbulence generators
Main flow with sufficiently low turbulence intensity
Usage of small scale wind tunnel
Improvement of the velocity profile, unification
Measurement of the turbulence, attempt to reduce it
Installation of several types of flow straighteners
Measurement of different compilations using CTA technique
Evaluation and comparison of the results
Choose the most appropriate compilation
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Turbulence generators
Laboratory application
Passive and active generators
Advantages/disadvantages
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Development of novel experimental turbulence
generator
Development of the wind tunnel
Previous measurements in a mini wind tunnel before designing the new one
Role of the flow straighteners
Effect of the length of the tunnel section
Practice of the CTA measurement technique
The application of the results
Design of small scale wind tunnel
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The layout of the wind tunnel
Based on previous measurements, increase the length of the tunnel section and the cross section was required
5600x400x400 mm
More powerful radial blower
Buffer box
Easy opening upper sheet for the change of flow straighteners
Test section made of Plexiglas: PIV and LDV measurements are possible
The assembled wind tunnel
Set the air velocity: using frequency converter
Need of bypass mode: jalousie on the buffer box
Flow straighteners were inserted into the tunnel section
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The assembled wind tunnel
Jalousie was placed in front of the ventillation intake: bypass- mode
Operation in lower velocity interval: 0-2,5 m/s
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CTA measurement technique
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In-point measurement
Perfect for measuring turbulence
Computer controlled traverse system
High sampling rate
Low noise ratio: 1/10000
Investigation of different flow straightener variations
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Case 1: empty tunnel section without metal net, only with a dust filter
Case 2: flow with two metal nets, with the distance from the exhaust of 4000 and
4500 mm
M=5 mm, d=1 mm
Passive turbulence generators
Investigation of different flow straightener variations
10
Case 3: 2 metal nets with the distance from the exhaust of 4000 and 4240 mm, between them tube bundle with
diameter of 6 mm
Measurements in each cases at two different frequency of power supply: 20 and 50 Hz
Investigation of different flow straightener variations
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MATLAB script
Post processing of the dataset obtained from the CTA software
Spatial coordinates, mean velocity, velocity RMS matrix
Display of mean velocity fields, histograms
Illustration of turbulence profile
Computing of spatial averaged quantities:
, ,
The deviation of the velocities at the investigated surface:
Results
The measurements were done perpendicular to the main stream, at the distance of 100 mm from the exhaust
Due to the mount of the CTA probe, only the central section (350x350 mm) was measured
Turbulent velocity profile: Case 3 at 20 Hz
0 0,5 1 1,5 2 2,5 3 3,5 4
0 50 100 150 200 250 300 350 400
Time averaged velocity [m/s]
Horizontal direction perpendicular to the air flow[mm]
350 mm
Results
Case
1 3,496 0,1521 4,289 10,237 0,2643 1,984 2 3,375 0,1112 3,894 10,270 0,1089 1,277 3 3,135 0,0544 3,498 9,885 0,1171 2,014
20 Hz: monotone decreasing values
50 Hz: fewest turbulence at Case 2
Presumption: higher air speed, vortexes have less time to decaying vortexes in the test section
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Results
Time averaged velocity profile in Case 3, at 20Hz
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Results
Turbulent intensity in Case 3, at 20Hz
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Results
The turbulent intensities in the 3 cases at 20 Hz, illustrated by histograms
The most frequent values and the width of intervals are different
Conclusions
It can be seen, that the flow straighteners have significant effect to the fluidic properties
Based on the presented measurements, the flow is nearly adequate for the turbulence generator experiments
Further flow straightener variation measurements
Find the most appropriate wind tunnel setup: unified velocity and turtbulence profile
Construction of the designed novel active turbulence generator
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The described work was carried out as part of the TÁMOP-4.2.2/B-10/1-2010- 0008 and the TÁMOP-4.2.1.B-10/2/KONV-2010-0001 projects in the framework of the New Hungarian Development Plan. The realization of this project is supported by the European Union, co-financed by the European Social Fund.
Email: aramszn@uni-miskolc.hu
2013.
