Customer Solutions

Instrumentation For National Wind Tunnel Facility at IIT Kanpur

Author(s):

Kamal Podda, Indian Institute of Technology

Industry:

Aerospace/Avionics

Product:

Data Acquisition, LabVIEW, Motion Control, Vision

The Challenge:

To develop an integrated, low cost, modular system for data acquisition and control for a 3m 2.25m closed-circuit low speed wind tunnel.

The Solution:

Develop a LabVIEW based DAQ and Control system running on a network of four PCs using DAQ boards, FlexMotion, and IMAQ.

Introduction
The recently established National Wind Tunnel Facility (NWTF), a 3m ´ 2.25m closed-circuit low speed wind tunnel, at IIT Kanpur uses Virtual Instrumentation (LabVIEW) for all its control and data acquisition functions. Such Wind Tunnels are the workhorses of industry and are extensively used in Aerospace, Automotive, Environmental, and Civil Engineering industries.

Deviating from the general practice of using a workstation for data acquisition and control, the entire control and DAQ function has been implemented using a network of PCs. Standard data acquisition (DAQ), Motion Control, and Image Capture hardware have been utilised in the instrumentation of the tunnel. Various operations which had to be integrated into the system include: Motion control of sting type model mount system, turntable (dual synchronous, and single), and 3-axis traverse, Flow visualisation with image acquisition, Multipoint (currently 352) differential pressure scanning, Hot Wire Anemometry, Force and moment measurement using internal balances, Roll, Pitch and Yaw angle measurements, and Noise and temperature measurements.

Off the shelf hardware from National Instruments including standard DAQ boards, FlexMotion, IMAQ, SG-2043 signal conditioners, Analog Devices 5B modules, and accessories have been used to implement all the functions on a network of four PCs. Out of these three systems are for control and DAQ functions, while the fourth unit is dedicated as a User Station. This arrangement provides the required flexibility and security for the operation of the wind tunnel.

System Configuration
The four PCs are configured as follows: The first (Master) unit handles all communication and will also control the main fan motor (1000kW) drive and safety interlocks of the tunnel. The second unit handles the pressure measurements using PSI pressure scanners and force and moment measurements through two PCI-6024E DAQ cards and SC-2043SG. The third unit is assigned to hot wire anemometry using Dantec Streamline CTA System through AT-MIO-16E-1 and motion control of the sting support mechanism through FlexMotion. In addition, it also manages the image acquisition (IMAQ) from the flow visualisation system. The fourth computer is configured as a User Station with a dedicated DAQ facility. Another system is to be added in the near future to reduce the load on the second and third systems.

Salient Features
Motion Control: The FlexMotion based sting support model mounting system as shown in the picture (with closed loop servo controlled hydraulic motors) is one of the most versatile systems in use, providing angular (±20° in pitch and yaw with full 360° roll) and positional (Vertical 1750 mm and Cross 2100 mm) movements. The accuracy is ±0.01° in roll & pitch, ±0.05° in yaw), ±0.13 mm vertical and ±0.08 mm cross. Five independent motions, e.g., pitch, yaw, roll, and vertical and cross translation can be simultaneously applied statically or dynamically. This permits simulation of various real life situations like, heaving, pitch and roll oscillations, etc. Siemens Simatic system is being used for the turntable systems. However, given the success of the FlexMotion system on the Sting Support Mechanism, replacement of the Simatic system by FlexMotion is under consideration. The three-axis traverse system (currently with independent controls) will also be moved to FlexMotion control.

Pressure & Flow Measurements: Pressure measurements form the heart of all wind tunnel instrumentation. The system as shown below has been developed to support up to 16 pressure scanners without any changes in the DAQ system. Therefore, in principle up to 1024 channels (16 scanners with 64 ports each) can be supported. Currently the Wind Tunnel provides 352 channels through 11 scanners of 32 ports each. These are supplemented by free-stream velocity measurements, and hot-wire anemometry.

Force Measurements: Two six-component Strain Gauge Balances are available for force and moment measurements. Data from either of these balances can be recorded through the PCI-6024E and SC-2043SG combination. A VI based system for on-line acquisition, analysis and display of actual forces and moments has been implemented.

Flow Visualisation & Image Acquisition: A light sheet using a 6W argon-ion laser is available for flow visualization, with three CCD cameras and recording system. The images can also be captured and analysed using IMAQ hardware (PCI-1411) and software (IMAQ vision).

About the NWTF
A state-of-the-art ‘3m x 2.25m Low Speed Closed Circuit Wind Tunnel’ with considerable associated equipment and instrumentation has been established in January 1999 at the Indian Institute of Technology Kanpur as a National Facility to meet the national need in the area of transport aircraft testing, non-aeronautical applications, and related R&D work.

This wind tunnel is of return circuit type with continuous closed jet test section (cross section 3 m ´ 2.25 m) at atmospheric pressure. The flow quality at the test section is: local deviation in static and dynamic pressure less than 0.3 percent; local deviation in flow angularity better than 0.1 degree; turbulence level less than 0.1 percent; local temperature deviation smaller than 0.5 degree Celsius. The tunnel has a contraction ratio of 9:1, and the maximum speed that can be generated in the test section is 90 m/s, yielding a test Reynolds number of about 6 million/m.

The various model testing capabilities of NWTF include (a) Full-model tests with sting support mechanism; (b) Half-model testing with external balance; (c) Two-dimensional model testing; (d) Ground effect simulation with moving belt; (e) Gust and cross wind simulation, and (e) Aero-acoustic testing.

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