Wind tunnel

The Newton laboratory has recently completed the installation of a 280 kWatt subsonic wind tunnel.
The air is designed to flow in a closed return wind tunnel, Goettingen type. The test facility has been built to run with either an open or closed test section, as needed for particular experimental program.

The required electric energy required is produced by mean of a power generator fully integrated with the wind tunnel.

Wind tunnel Wind tunnel Wind tunnel

Wind tunnel Wind tunnel Wind tunnel

Wind tunnel Technical specifications

General

Single return closed circuit (Gottingen type)
Dimensions: 27m long, 4,5m wide, 8m high
Rectangular air path perimeter along centreline: 56m
Construction material: steel
Maximum power available: 280 kWatt

Test sections

Section A: 1,25mX1,25m, 1,6mq, max speed 280 kmh, nozzle 10,2
Section B: 1,5mX1,5m, 2,3mq, max speed 190 kmh, nozzle 7,1
Section C: 1,9mX1,9m, 3,6mq, max speed 125 kmh, nozzle 4,4

Test chamber

Open or closed (with adjustable slotted walls max 30% open)
Screens: n. 1 honeycomb + 2 turbulence screens

Fans

n. 4 axial fans, diameter 1250mm each
Total fan power: 210 kWatt

Instrumentation

6 componets balance (n. 3 load cells + n. 3 torque meter)
Pressure measurements: n. 20 ports available
Acoustic: n. 4 microphone

Control and data acquisition system with post processing

Computers: n. 2 + Windows O.S.
Software: control software by AD Engineering (BG-IT), data acquisition system with post processing by
Newton S.r.l.

Wind tunnel Test sections

Three test sections with a length of 5m are currently available.

Test section

Maximum speed

Contraction ratio (nozzle)

Length to hydraulic diameter ratio

1,25mx1,25m - A=1,6mq

280 kmh

10,2

4

1,5mx1,5m - A=2,3mq

190 kmh

7,1

3,3

1,9mx1,9m - A=3,6mq

125 kmh

4,4

2,6

Other test sections can be produced on demand.

Wind tunnel Wind tunnel Wind tunnel

Wind tunnel Wind tunnel Wind tunnel

Closed return wind tunnel advantages

Through the use of the corner turning vanes and screens, the quality of the flow is controlled with high accuracy.

The noise of the wind tunnel is kept low and it does not affect the results in the acoustics measurements test sessions.

Less energy is required for a given test section size and velocity: this aspect is important when completing developmental experiments with high utilization.

There is a reduced environmental noise when operating.

Wind tunnel Sample dimensions

Experiments to obtain aerodynamic parameters that affect automobile performance, engine cooling, brake cooling and wind noise are made with either at full scale or with scale models.

A key issue for automobile testing is the blockage based on frontal area= the ratio of the model frontal area to the test section area.

The flow around automobiles is often more characteristic of “bluff bodies” than of “streamlined bodies”: this means that there is always a sizable region of separated flow. The wind tunnel test section needs to be sufficient long so that these separated flow regions “close” before encountering the end of the test section and the entry of the diffuser.

In such case it is really helpful to use Newton Wind Tunnel in the open test session configuration.

For experiments with large objects in which the model is held stationary during data gathering and the maximum speed is below 0,3 Mach (350 kmh) it is possible to apply the similarity approach in order to work on a scaled model.

By keeping the same Reynolds number the model and the full scale flows will be dynamically similar: the non dimensional functions for fluid velocity components, pressure coefficients, density, viscosity, the force and the moments will be the same.

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Wind tunnel Test models

It is possible to realize test models starting from the 3D CAD drawing to the final CNC sample.

Wind tunnel Wind tunnel Wind tunnel

Wind tunnel Measurements on the model

Force and moments

At present time the force and moments to calculate the aerodynamic forces are acquired by mean of n. 3 load cells and n. 3 torque meters.

For the actual tests regarding the aerodynamic characteristic of helmets this system has been embedded inside a standard headform.

Wind tunnel Wind tunnel Wind tunnel Wind tunnel

Pressure mapping

The model can be special prepared in order to accommodate small tubes (2mm diameter) to acquire the local pressures. At present time up to 18 pressure locations can be acquired.

Surface flow visualization

Information about the flow on the surface of the model being studied helps to investigate stagnation point locations, separation lines, location of boundary layer transition.

In Newton lab we commonly use a smoke generator or, alternatively tufts. The tufts being light and flexible will align themselves with the local surface flow as a result of direct aerodynamic forces.

Wind tunnel Wind tunnel Wind tunnel

Wind tunnel Termodynamics

We have realized a new test headform all covered with thermocouple.

This headform will be used to measure the effect of the ventilation of the helmet.

The software, developed by Newton, shows the 3D model of the head and it represents with colored contour style the various temperatures of the head.

At the beginning the head is red and then, thanks of the air inlet/outlet some areas with different colors appear in relation to colder areas.

We can apply up to 32 thermocouples on a real athlete/tester that is practicing in front of the wind tunnel. We can monitor the temperature to check the ventilation and thermal behavior of the clothing.

Wind tunnel Wind tunnel

Wind tunnel Acoustics

The headform used in the aerodynamic test is equipped with two microphones at the auditive meatus level.

It is possible to measure the noise produced by the air stream on the helmet: the measurements include the sound level [dB(A)], the octave analysis, the frequency analysis.

Wind tunnel Turbulence Level

Variations in flow quality between different wind tunnels will cause variations between the results obtained when experiments for the same Reynolds number are performed. One of these flow quality parameters is turbulence level.

Turbulence spheres were used to obtain drag coefficient measurements for a range of Reynolds number flows.

The critical Reynolds number for freestream atmospheric transition was taken to be 385,000 and was divided by the measured critical Reynolds number to obtain a turbulence factor.

This comparison with the 5,5 inch turbulence sphere yielded the turbulence factor TF=1,02: the result indicates that the Newton wind tunnel has an excellent quality of flow with freestream turbulence levels below 0,2%.

Wind tunnel Wind tunnel

Wind tunnel Software and control

The control of the wind tunnel is completely separated from the data acquisition activities.
Two separated computer systems are used: the first control the speed of the wind and all the safety procedures, the second is dedicated to data acquisition (up to 32 channels) and post processing.

The software can be personalized on the base of special requests.

Wind tunnel

Wind tunnel References

Low-Speed Wind Tunnel Testing di Jewel B. Barlow, William H. Rae, Alan Pope
Performance testing using standardized wind tunnel (Newton laboratory internal procedure n. MPI-MWT-01)