UWE’s School of Engineering places strong emphasis on hands-on, experiment-led teaching. A critical asset supporting this approach is a large wind tunnel originally designed in the 1960s. It is used daily during teaching modules and postgraduate research across aerospace, mechanical, civil engineering and architecture.
The wind tunnel is driven by a 120 kW DC motor, housed within a 1.35 m diameter nacelle, and capable of delivering controlled airflow speeds suitable for aerodynamic testing. The reliability and stability of this system are critical to both safety and the accuracy of experimental results.
The Challenge
After more than 35 years without service, the wind tunnel’s main fan unit began exhibiting abnormal noise and unstable speed behaviour. These symptoms compromised test repeatability and raised concerns as the university worked to bring the facility in line with modern safety and regulatory standards.
Compounding the above and that access to the motor was severely restricted due to its location within the wind tunnel structure. Initial internal assessments suggested that full removal and replacement of the motor would require dismantling parts of the building, with estimated costs exceeding £2 million and months of downtime.
UWE required a solution that reduced risk, controlled cost, and avoided unnecessary replacement—while delivering confidence in long-term operation. Since we have dealt with them in the past, we were their first point of contact.
The Solution
Our experienced engineers proposed a phased, condition-based engineering approach, allowing decisions to be driven by measured data rather than assumptions. This ensured risk was managed progressively and that intervention was proportionate to the actual condition of the asset.
Phase 1: Initial Inspection & Access Planning
Our engineers carried out an initial site visit to assess safe access to the motor. This involved planning and executing the removal of the wind tunnel tail cone and confirming lifting, rigging, and working arrangements within the confined cylindrical structure.
Once exposed, the system was confirmed to be a 120 kW DC motor, with visible degradation to the brush gear and lubrication system consistent with long-term inactivity. A visual inspection was completed, and a phased investigation plan was agreed with UWE.
Phase 2: Condition-Based Monitoring
To establish the true mechanical and electrical condition of the system, a vibration analysis condition assessment was carried out. Data was collected across the operating speed range, including Velocity, Acceleration, and PeakVue bearing measurements.
Key findings included:
- Overall vibration levels within ISO 10816 / 20816 limits
- Fan blade imbalance measured at <1 mm/s RMS, an excellent result for a system of this age
- Elevated bearing stress at the drive end, consistent with lubrication degradation rather than mechanical failure
- Low-level electrical activity indicating load instability rather than terminal damage
These results confirmed that the motor remained fundamentally sound and that full removal was unnecessary.
Phase 3: On-Site Refurbishment
Based on the condition assessment, we completed a comprehensive refurbishment entirely on site, avoiding removal, transport, and structural modification.
Work included:
- Full overhaul of the DC brush gear, freeing seized brushes and reinstating degraded components
- Commutator inspection, undercutting, and polishing to restore even brush contact and promote controlled wear
- Replacement of the non-drive-end bearing, heated to 120°C prior to installation to ensure correct fit without inducing mechanical stress
- Electrical cleaning and drying, restoring insulation resistance and improving overall electrical integrity
- Installation of dedicated lubrication pipework, allowing routine greasing without dismantling the wind tunnel
All work was delivered in phased site visits to accommodate the university’s teaching schedule.
Phase 4: Testing & Validation
Following reassembly, the system underwent a structured programme of electrical and operational testing.
Insulation resistance and continuity testing confirmed strong electrical integrity across the motor. Operational run-up testing demonstrated stable performance throughout the speed range. During full-load validation, the fan operated at 500 RPM, drawing 100 amps at 320 V DC, confirming a stable and reliable performance profile for equipment of this scale and age.
Noise levels were audibly reduced, and speed stability was restored, providing confidence in both safety and test accuracy.
The Results
The wind tunnel has been successfully returned to reliable service, delivering stable airflow essential for aerodynamic testing and teaching. By completing the work on site, months of downtime was avoided, the need for building alterations – eliminated, and capital expenditure exceeding £2 million -prevented. The refurbishment has extended the service life of a critical legacy asset while improving its long-term maintainability through enhanced lubrication access and condition-led monitoring.
“The overall engagement with the Mawdsleys team was very good and extremely helpful. They were highly knowledgeable and worked with us to solve a complex problem quickly, using the resources available and at a very reasonable cost. What really stood out was their approach — instead of immediately pushing for removal or replacement, they suggested measuring the vibration first and exploring on-site solutions. That saved a huge amount of time, cost and disruption. We would absolutely recommend their service.”
Samson Annapureddy
Lecturer in Experimental Aerospace Engineering, UWE Bristol
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