"We used a combination of LabVIEW software and NI high-speed data acquisition hardware to collect all necessary data and process it for dynamic derivatives of the oscillating aerospace model."
- Dheerendra B. Singh,
National Aerospace Laboratories (NAL)
The Challenge:
Developing a highly reliable, user-friendly system to acquire, monitor, and process data in real time for the oscillating aerospace models in a 1.2 m Trisonic wind tunnel.
The Solution:
Using an NI PCI-4474 dynamic signal acquisition (DSA) module and an NI USB-9233 DSA module to simultaneously collect data and, along with NI LabVIEW, process the data for accurate amplitudes, phase, and frequency measurements.
Author(s):
Dheerendra B. Singh -
National Aerospace Laboratories (NAL)
K Prasad Rao -
National Aerospace Laboratories (NAL)
The 1.2 m blowdown wind tunnel at NAL is an intermittent facility that provides steady airflow from about 20 seconds (at Mach 4.0) to about a minute (at Mach 0.2). The test section has a dimension of 1.2 m by 1.2 m. To measure dynamic derivatives on a flight vehicle model, we developed a single-degree-of-freedom (SDOF) forced oscillation rig for data generation.
System Overview
The model is supported on an SDOF elastic suspension system created by a flexure pivot. An electrodynamic shaker, combined with a power amplifier, a closed-loop control system, and a link, sets up steady oscillation at or near the resonant frequency of the model-flexure pivot combination. The flexure pivot and the link are instrumented with strain gages to measure the model angular displacement (Ɵ) and the exciting moment (T).
The system based on LabVIEW uses NI PCI-4474 and NI USB-9233 DSA modules for data acquisition, monitoring, and processing. Aerodynamic data on the model is derived by measuring the model response and the exciting moment when the model performs constant amplitude oscillation at the desired frequency and amplitude, initially in wind-off, and subsequently at the required wind-on condition.
For monitoring the forced oscillating aerospace model during the blowdown condition in the Trisonic wind tunnel, we acquire the data using PCI-4474 and USB-9233 DSA modules in parallel. The system monitors the basic condition for resonance between forcing function and response on the dial gauge, which helps the operator make decisions about whether the model is oscillating at resonance or not. If the resonance condition is not met within a specified time, the operator may stop the blowdown sequence to save valuable energy.
The basic rig motion signal and a reference signal are acquired using the PCI-4474 and processed using digital filter techniques in LabVIEW for accurate amplitude, phase, and frequency measurements. Model motion is acquired in parallel with the USB-9233 at different sampling rates to rotate the model based on the acquired response signal. Because model viewing is not available, acquired signals oscillate the image to simulate the tunnel condition. An theta signal acquired with the USB-9233 is used as an input to oscillate the image.
To suppress the noise, we incorporated a real-time digital filtering technique, which helps monitor the exact response from the strain gages. Because model and human safety is critical in the Trisonic wind tunnel, the system relies on LabVIEW to provide a highly user-friendly, flexible, and accurate platform to monitor the signals from the oscillating model and help the user make decisions to avoid catastrophic failures.
System Benefits
We used a combination of LabVIEW software and NI high-speed data acquisition hardware to collect all necessary data and process it for dynamic derivatives of the oscillating aerospace model. The amplitude data acquired by the USB DSA simulates the model rotation as it happens without compromising the acquisition rate, and the system can monitor the critical parameters of the oscillating model in real time. In addition, users can precisely analyze the amplitude of the model oscillation because unit cycle (frequency) remains fixed in the front panel.
We used LabVIEW for data acquisition, processing, and monitoring the forced oscillating aerospace model in the wind tunnel. The user-friendly system generates highly reliable data for our aerospace application.
Author Information:
DheerendraB. Singh
National Aerospace Laboratories (NAL)
NWTC Wind Tunnel Road Yemmalur Post Belur Campus
Bangalore
India
dbsingh@nal.res.in
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