Developing a Data Acquisition and Control System for a Trisonic Wind Tunnel

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"With reliable NI hardware and LabVIEW software for test and measurement, we are developing and deploying a rugged, and highly precise data acquisition and control system. The system is user friendly for novice users and provides low-level control over the tunnel for experienced users."

- Praveen Baburao, Captronic Systems Private Limited

The Challenge:
Automating and controlling the various operations of a 0.3 m wind tunnel that runs in subsonic, transonic, and supersonic modes.

The Solution:
Automating and controlling the movement of the model based on a predefined sequence inside the wind tunnel and monitoring system parameters, alarms, and interlocks in real time while achieving the desired MACH number within the specified test time. We designed the data acquisition and control system for the trisonic 0.3 m wind tunnel using NI PXI hardware and NI LabVIEW system design software.

Author(s):
Praveen Baburao - Captronic Systems Private Limited
Temin Sam Dalton - Captronic Systems Private Limited

Wind tunnels are an important testing tool for ground-based aerodynamics studies for aircraft and other moving objects. A large wind tunnel facility required a solution for automated control of the various operations of one of its wind tunnels. This tunnel was a trisonic 0.3 m wind tunnel for testing in subsonic, transonic, and supersonic modes. Reaching the desired MACH number within two seconds was one of the system’s key objectives. During the test runs, various interlocks had to be addressed to prevent accidents. Once the MACH number was achieved, the model under test was subjected to a range of linear and angular movements. The data acquisition system recorded important data through sensors mounted on the model.

System Architecture

The system controls the operation of the isolation valve (IV), pressure regulating valve (PRV), model incidence (MI), transonic model craft (TMC), and second throat flaps to ensure accurate and efficient control of the wind tunnel. The tests can run in three modes—subsonic, transonic, and supersonic. The tunnel operation can be further executed in three modes—auto, semiauto, and diagnostic/manual.

The air is stored in a reservoir with high pressure, and the isolation valve supplies this air to the tunnel. The isolation valve is operated through the digital output (DO) of the NI PXI-6514 module. The percentage of opening of the PRV valve (AO) is based on the MACH number that needs to be achieved and is implemented using a proportional integral derivative (PID) loop. The stagnation pressure (P0) and the percentage of valve opening are read as analog inputs via a Druck transducer for PID control. The static pressure (Ps) is measured from the settling chamber as analog input using the Druck transducer.

The MACH number is then calculated as the ratio of P0 to Ps. The TMC section and second throat section are used to vary the position of the vertical and horizontal control flaps, which helps the user achieve the MACH number accurately. These control flaps are also the analog inputs read from the potentiometer. All analog inputs are acquired using an NI PXI-6224 M Series multifunction DAQ module at high sampling rates. To control the PID loop, TMC, and second throat position analog outputs, an NI PXI-6713 high-speed analog input module is used. The model incidence section is the critical section where the position and the angle of the model are varied per the user configuration. This is accomplished using the hydraulic pressure, which is controlled by proportional valves, which are in turn controlled by analog outputs. During this, strain acting on the model is captured from various points at higher sampling rates using an NI PXIe-4330 simultaneous bridge input module. All the interlocks are handled using the digital I/O of the NI PXI-6514 module. The complete test can run for a maximum of 300 seconds. Separate mimic displays, provided with the touch panel monitor display, depict the actual flow of the tunnel.

System Operation

Before running the tunnel, all the interlocks are checked. If all the interlocks are satisfactory, the IV is opened to supply air to the tunnel. The PRV is opened initially in position mode and then in pressure mode. Based on the MACH number to be achieved, the respective P0 is taken as a setpoint for the initial opening of the PRV. Then, based on the Ps and P0, the MACH number is calculated. If a MACH number is not yet achieved, then the PRV is opened some more and the same calculation is completed again. For subsonic and transonic modes, in addition to the PRV, the TMC and second throat control flaps are varied to achieve the required MACH number.

Once the MACH number is achieved, the linear and angular movements of the model start running based on the configurations from the user in the Run Configuration window of the software. The model can be moved in two modes—pitch and heave. In pitch mode, the model is moved up and down linearly. In heave mode, it is moved angularly. In each mode, the user can configure for step mode, continuous mode, and preposition modes. The model should respond to the movements in a specified time accurately; failing to do this indicates a faulty model. Faults in the tunnel during the run trigger an alarm module, which generates the alarm and shuts down the tunnel.

The Software

The control system application software provides the following modules:

  1. Login
  2. Main
  3. Mimic
  4. Channel Setting
  5. Calibration
  6. Parameter Setting Limit
  7. Diagnostic
  8. Alarm
  9. Run Configuration
  10. 0.  Run
  11. 1.  Data Logging
  12. 2.  Report Generation

Figure 1. Control System Overview

Figure 2. Main Panel of Test Application Software

Figure 3. Mimic Panel of the Actual Tunnel

Figure 4. Diagnostic Panel

Figure 5. Run Configuration Panel

Figure 6. Run Panel

The Benefits of Using the NI Platform for Our System

With reliable NI hardware and LabVIEW software for test and measurement, we are developing and deploying a rugged, and highly precise data acquisition and control system. The system is user friendly for novice users and provides low-level control over the tunnel for experienced users. The high data acquisition speed and processing capabilities of NI hardware made it possible to have multiple simultaneously executing PID control loops. Overall, the fully automatic control and test system we delivered increased research activity in the aerospace laboratory and reduced testing time.

Author Information:
Praveen Baburao
Captronic Systems Private Limited
No.03, Victorian Meadows Airport-Varthur Road
Marathahalli Bangalore-37
India
Tel: 9916877405
Praveen.b@captronicsystems.com

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