Instrumentation

Stability Wind Tunnel Instrumentation

Data Acquisition Equipment

The centerpiece of the system is a SCXI-1001 Mainframe from National Instruments. The mainframe allows for the installation of up to 12 SCXI modules which may perform any desired signal conditioning and sampling of the input signals. Currently four SCXI-1120D isolation amplifier modules are installed in the mainframe. Each of these modules allows isolation and amplification of 8 differential analog voltages with an input range of -10 to +10 volts. Each module multiplexes the 8 inputs which are read by a National SCXI-1600 module, the SCXI-1600 is a USB data acquisition (DAQ) device that features a 16-bit ADC. The SCXI-1600 receives analog signals from other SCXI modules and amplifies, digitizes, and sends data through a USB port. This results in a total of 32 isolated differential analog input channels with an Analog to Digital conversion resolution of 16 Bits. All of the software for data acquisition is written using LabView. Collected data can be stored on the computer hard drive, and then transferred to via usb flash drive, CD, FTP, or e-mail (through wired or WiFi networks).

Forces and Moments

The tunnel is equipped with three; six component strain gauge balances for both sting and strut model support systems. All balances were manufactured and calibrated by Modern Machine and Tool, Inc. Table 2 gives the balance load limits. Balance excitation and signal amplification is provided by the National Instruments SCXI-1520 is an 8-channel universal strain gage input module that offers all of the features you need for simple or advanced strain measurements. With this single module, you can read signals from strain, force, torque, and pressure sensors. The NI SCXI-1520 includes an onboard reference for automatic calibration in changing environments. It offers a programmable amplifier and programmable 4-pole Butterworth filter on each channel. Each channel also has an independent 0 to 10 V programmable excitation source.

Table 2: Standard Tunnel Balance Limits

Pressure, Velocity and Turbulence

Pressure, velocity and turbulence measurements can be done through a large array of state-of-the-art instrumentation including multiple channel pressure scanning system, constant temperature and laser Doppler anemometry and particle image velocimetry. Additionally single microphones as well as 64 and 128-microphone phased arrays are available.

Multi-channel Pressure Scanner
Dynamic pressure in the test-section is read using a Datametrics Model 590D transducer with a traceable calibration. An Esterline Pressure Systems 144-channel pressure scanning system (98RK frames with 9816 series modules) is available for measurements. This system allows the simultaneous measurement of pressure on 96 channels for pressures up to 10 inH2O and 48 channels for pressures up to 2.5psi. The pressure scanner comes with a traceable and up-to-date calibration. Such system is ideal for measuring surface pressure distributions and mean wake or boundary layer profiles.

Constant Temperature Anemometry
Unsteady velocities and velocity spectra measurements can be made with the constant temperature anemometry system available. Straight type single and four-sensor miniature hot wire probes permit measurements of three-dimensional mean velocity, turbulence quantities, and spectra. Probes are balanced and operated using a Dantec 90C10 Streamline bridge system. An Agilent E1432 16-bit digitizer (with a maximum sampling rate of 51.2kHz with built-in anti-aliasing filters) is used for data acquisition. Flow temperature is monitored continuously during hot wire measurements and corrections made using the method of Bearman (1971).

Stereoscopic Particle Image Velocimetry
The Stability tunnel is equipped with a state-of-the-art LaVision stereoscopic PIV system for instantaneous 3-component velocity measurements over a plane. This system will be measurements at the base of a model trailer, with and without drag reduction devices, to provide quantitative flow data on the separation and wake structure for comparison with, and validation of, the CFD. The system, acquired in 2006, features a 200mJ dual cavity pulsed Nd:YAG laser and two 4 megapixel 14-bit CCD cameras and can image seed particles at any point within the Stability tunnel test section over an interrogation area of up to 30x30cm. The two cameras provide the stereoscopic capability. While the most obvious benefit of this is the measurement of the out-of-plane velocity component, the use of two cameras also allows the elimination of parallax errors and the self-calibration of the camera image plane; after an initial approximate calibration using a target, the system uses the PIV images themselves to infer the location and orientation of the measurement plane. The software allows for a range of image processing options that, for example, eliminate peak-locking, or allow removal of unwanted images features.