Equipment and resources in the laboratory of fluids and thermal science

Traversing systems

Several modular highly accurate and heavy-duty external traversing systems are available in the laboratory for accurate positioning of probes, lasers and cameras. Most is connected for Labview and can be synced with sampling. One of them is an accurate and heavy-duty six-axis ABB-PS 60/4-50-P-LSS 36/2 robotic arm.​​

Pressure probes

A large set of pneumatic probes is available in the laboratory, and new probes can be built to suit the requirement for the measurement. Additive manufacturing is used to produce probes with complex shapes in metal (Ti/Inconel) with pneumatic channels down to 0.3 mm inner diameter. As well, traditional manufacturing methods are used to manufacture probes from stainless steel pipes with the inner channel diameters down to 0.15 mm. The possibility to customise probes and an in-house calibration process make the pneumatic measurement very versatile. A selection of existing probes and their dimensions are summarized in Table 4.5. Typical results from a flow field measurement by a multi-hole probe are shown in images below where the total pressure coefficient, swirl angle and streamwise vorticity are shown.​

List of available pneumatic probes in the laboratory:

Probe calibration facilities

Calibration of the probes is performed either in an in-house dedicated calibration facility or in-situ in the wind tunnels. The calibration is traceable and repeated at regular intervals. The dedicated calibrator is versatile, so that straight, L-shaped, and other probes can be mounted. The calibration process is fully automated. Probe positioning is performed by servo-motors with high-resolution optical encoders. Probes are calibrated in a jet flow and achievable cone angles are up to 150° but a typical standard range is below 60°. A blockage correction from the probe blockage is applied. The resolution of the calibration matrices is down to 0.2° in pitch and yaw angles but are adjusted for each case. Probes are typically calibrated at velocities from 5 to 60 m/s, limited by the measurement range of the reference manometer FCO 510/560 (Furness Control) but higher velocities are possible as well. Commercial and in-house software is used for data reduction. In-house calibration method, data reduction, error analysis and measurement corrections are described in Hjärne (2007), Chernoray and Hjärne (2008), Axelsson (2009), Arroyo (2009) and Rojo (2017). 

A stand-alone data reduction script from Aeroprobe Corporation and calibrations performed by Aeroprobe Corporation are available for the commercial probes.

Surface pressure measurements on OGV and Endwalls

Surface static pressure distributions can be measured by embedded surface pressure taps. The aerodynamic surfaces are either instrumented by drilled holes and metal pipes or models with embedded pressure taps are manufactured by rapid prototyping methods. With a typical rapid prototyping by stereolithography (SLA) the surface pressure tap diameter is 1.2 mm and the diameter of the connecting lines is 1.6 mm. A know-how of the laboratory is a custom quick mount connector which can be directly attached to an embedded counterpart in a model. The quick mount connector is directly embedded in the model and an example of the surface pressure data from the pressure taps is shown as well. Normal recommendation are to keep the number of channels below 146, but more can be used but this requires manually change the port configuration.​

Pneumatic transducers

The lab possess three 16-channel PSI 9116 units from Pressure Systems Inc with a 500 Hz sampling frequency. With a custom calibration, the PSI-9116 unit provides a pressure measurement uncertainty of 0.1% in the pressure range from 500 to 2500 Pa and an uncertainty of ±1 Pa in the range from 0 to 500 Pa.

When the allocated space is limited, miniature pressure scanners are used. The laboratory has two 32-channel ESP-32HD digital miniature pressure scanners with a DTC-Initium unit from Pressure Systems Inc. The two ESP-32HD units have a measurement range of ±2500 Pa and an accuracy of ±1.5 Pa.

As a high-accuracy reference, four FCO 510 micromanometers from Furness Control are used. There are two units with a 200 Pa measurement range and two units with a 2000 Pa measurement range. The FCO micromanometers are calibrated annually by a certified company. The accuracy of the manometers is at least 0.25% of the reading and better than 0.025% of the measurement range.

A single FCO560 2000Pa is used for calibration using its internal pressurising pump with an accuracy of 0.1% of the reading + 0.003Pa.

A few enhanced FCO432 is used in the lab for high accuracy pressure measurement.

For time-resolved pressure measurements, 10 Kulite sensors are available. A large amount of miniature single-channel absolute and differential pressure transducers is available as well. The transducers have a typical measurement error of 0.5-0.75% of the full scale.

All pressure transducers are currently incorporated into an automated data communication and measurements protocol.​

Hot wires and hot films

Boundary layer velocity profiles, time-resolved velocity, turbulence level, turbulence dissipation, intermittency and laminar-turbulent transition are measured by the hot-wire anemometry (HWA). Several multichannel HWA systems from Dantec (DISA 56C17 and mini-CTA) are available in the laboratory. Over 100 single and X-wire probes from Dantec are available as well as film sensors from Senflex. The hot-wire probes are mounted in the same traversing systems as multi-hole probes.

The laboratory has a long tradition and experience of using the Hot Wire Anemometry (HWA) technique, see Bakchinov et al. (2001), Chernoray (2007), Chernoray, Ore, Larsson (2010), Chernoray et al. (2010), Jonsson et al. (2018). Custom in-house hot wire probes, miniature hot wire probes and MEMS-probes are manufactured in the laboratory, see e.g. Gibson et al (2004).

The hot wire probes as resistance thermometers (cold wire mode) are used to measure the temperature of the flow. The wall-mounted hot films can be used for laminar-turbulent transition detection and as resistance thermometers for wall temperature measurement. However, our experience shows that the wall film probes can potentially disturb the flow. Specially designed surface cavities can be used to embed the film probes and to minimize the disturbances. Due to these complications, the priority is given to the hot wire probe traversing which are proven do not affect the transition location and more versatile than hot films.

Surface oil-film visualization, tuffs and smoke

A typical surface oil-flow visualization is shown in Figure 4.12 with highlighted streamlines and reference coordinate lines. This technique is used as a qualitative tool to identify topological surface structures on the vane, hub and shroud. The facility is instrumented with an embedded video camera for photo and video recording of the oil-film development. An oil-kerosene mixture with pigment particles is adapted for operating velocity and blade loading by changing proportion of the components to control the evaporation rate and viscosity of the mixture. Tuffs and smoke is commonly used as well to flow visualisation, its shown to the right below on a truck tested in the L2 windtunnel.

Temperature and heat transfer measurements

A set of modern equipment for temperature and heat transfer measurements is available in the laboratory. Heat transfer measurement via IR-thermography was first established by Arroyo (2009) and further developed by Rojo et al. (2013, 2014). Different heating/cooling sources are used to achieve the temperature difference between the surface and the flow, such as electric cartridge heaters, water circulation channels, heat foils and radiative heaters.

The primary tool used in the laboratory is the IR-thermography but the liquid crystal thermography and naphthalene sublimation are used as well. A large amount of resistance temperature detectors (RTD) with traceable uncertainty down to 0.02K, thermocouples (TC), miniature thermocouples, cold-wire probes and film probes is available. Corresponding DAQ equipment such as several units of NI-9217, NI-9214 and SCXI-1520 from National Instruments is readily available. The temperature calibrations are reference traceable.

IR-Thermography

This is the primary method for surface temperature measurements in the laboratory see Fig. 4.13. Heating of the models is realized either by heat foils as in Wang et al. (2013, 2016) or by electrical/water heating systems as in Arroyo (2009) and Rojo et al. (2013, 2014). A recent development is using rapid prototyping for manufacturing a vane with a section of hub and shroud with an embedded water channel system REF TO ETC. The new improved technique reduces uncertainties associated with the wall thickness non-uniformity and thermal conductivity variations. The new method provides substantially reduced manufacturing and instrumentation time at reduced model cost. The IR system used in the laboratory is from Phoenix with a 320 × 256 sensor and a frame rate of 122 Hz at full-frame. In-house developed control and image processing software is used to achieve high accuracy measurements and flexible post-processing. For bigger frame or faster sampling, we have the ability to rent cameras from FLIR.

Unsteady IR-Thermography

The IR camera if often used as for flow visualisation by study the temperature fluctuations on the surface, this is non-intrusive method often used in the wind tunnel testing to detect vortex or transition location. For simpler tests this is done by external heating such as directional light but can be done with dispersed PIV laser or internal heating as well for more advanced testing. Below there is an example from OGV-LPT tunnel to the left where the high temperature fluctuations represent the transition point, and to the right the large scale vortices in a delta wing can be seen in the L2 tunnel.​

Liquid Crystal Thermography

In applications where the access for an IR-camera is limited a Liquid Crystal Thermography (LCT) technique is used as an alternative method for surface temperature mapping. Figure 4.15 shows typical LCT images and Nusselt number distributions from a liquid crystal thermography measurement obtained in the CHALMERS’ linear cascade (Wang et al. 2014).​

Naphthalene sublimation

This method is described in Jamshidi (2017) for heat transfer measurements in small cooling channels in an electric generator where optical access is not possible without substantially disturbing the flow field. The method was recently upgraded for improved measurement accuracy. An example test piece instrumented for naphthalene sublimation is shown in Fig. 4.16.​

Particle Image Velocimetry (PIV)

The technique is established in the laboratory since 2001. Currently, two PIV systems are available in the laboratory, from Dantec and LaVision. A cooperation with leading suppliers of the PIV software is established (Dantec, LaVision and the Institute of Thermophysics).

The equipment and software include a high-speed stereo-PIV system, a tomographic-PIV system, a long-distance micro-PIV equipment and endoscopic micro-PIV, see Figs. 4.17-4.18. Results obtained in the laboratory are published in recognized journals and conferences. Correspondingly, results from different PIV techniques are published in Hartono et al. (2014), Niebles et al. (2016), Minelli (2017), Zhao et al. (2016).

Other available measurement techniques

The laboratory is using many other measurement techniques such as oil-film interferometry, pressure- and temperature-sensitive paints, digital image correlation (DIC), force measurement etc. The equipment is available and the techniques are well-established.

Geometry control, measurement uncertainty, conformance and traceability

Care is taken to assess uncertainties for all measured quantities during all steps, from errors in the conversion of digital geometry formats to delivered results. To avoid any format conversion errors, the geometries are provided to the manufacturers in agreed format or when the manufacturer is using own conversion, the converted geometry is verified by us. The manufacturing drawings and specifications are established in a dialogue with our clients before manufacturing. Controls on the manufacturing are done for crucial parts to ensure manufacturing will be performed satisfactorily. Our standard procedure for geometric conformance control for an OGV after delivery is described below:

1. The geometry is inspected and returned if any visible errors can be detected.
2. The geometry conformance is controlled, either by a coordinate measurement machine (CMM) or a ROMER measurement arm with external optical scanning head or a ruby ball. This is done in a tempered room and an example of a scan of an stereolithography (SLA) rapid prototyped vane for heat transfer measurement. The equipment can accommodate accuracy down to ±0.005 mm (CMM), ±0.025 (ROMER+Ruby) and ±0.05 mm (ROMER+Optical) in a volumetric accuracy.
3. Surface roughness of aero- surfaces is inspected and measured:
   a. Either by a handheld roughness measurement device Surtronic 3+.
   b. Or by stationary machines as a Wyko Optical Profile or a surfscan S3 that provide a 3D surface topology.
4. Defects and leakages of internal channels are inspected and evaluated by pressurizing each channel and controlling the response with a pressure transducer.
   In addition, for the models instrumented for heat transfer measurements:
5. The wall thickness is measured with an ultra-sonic machine 38DL Plus down to ±0.005 mm accuracy.
6. Thermal conductivity of material samples is measured within ±1% or ±5% accuracy by HotDisk AB. The accuracy depends on sample dimensions.

Model manufacturing and modifications

We have selected to outsource most of our manufacturing as investment cost is too high to keep up with modern manufacturing methods for the production volumes we have. We do have a very good network of manufacturing and for most manufacturing methods we have a large pool and a large selection of different manufacturing. We also have some more in-house resources with both equipment and manufacturing from collaboration with other infrastructure and labs at Chalmers.

• Metal Workshop – Fully equipped manual metal workshop including; CNC, MDC, for minor modification or manufacturing series. (Chalmers Materials Analysis Laboratory)
• Metal Additive Manufacturing – (EOS 100, EOS270) for titanium, 718 and aluminium. We mostly print probes in this machine but larger object can be produced also. (Chalmers Materials Analysis Laboratory)

The manufacturing ability we have in the lab is the following:

• Plastic Additive Manufacturing – In the lab there is a Modix 3D printer with a print volume of 600x600x600mm for support models or more simple models.
• Hand Tools – In the lab there are hand tools for simpler modifications to a model, we do not recommend to make the model in our lab however.​