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Original design & manufacturing of a New Upstream Rotating Measurement System for gas turbine exhaust gases studies

Final Report Summary - NURMSYS (Original design & manufacturing of a New Upstream Rotating Measurement System for gas turbine exhaust gases studies)

Executive Summary:

The objectives of the NURMSys program consists on the design and manufacturing of a New Upstream Rotating Measurement System for gas turbine exhaust gases analysis.

Project Context and Objectives:
The Topic deals with the development of a new adaptable and reliable combustor test module, including measurement system, devoted to reverse flow annular shape combustors – used in helicopter engine for example. In fact, environmental concerns encourage gas turbine manufacturers to reduce pollutant emissions by improving combustion quality. To study combustion, it is essential to characterize exhaust burnt gases by measuring chemical species concentration, velocity, pressures and temperatures. These measurements are required to qualify the combustion efficiency allowing manufacturers to estimate fuel consumption, pollutants emissions and lifetime.

However, there are some difficulties when trying to obtain such crucial data because of severe environmental conditions (1600K). Efficient combustion study implies to pick up gases samples, directly at combustor exit and to convey them at controlled temperature to the gas analyser. Moreover, high temperature is a real threat for thermocouples and sensors.

Nowadays, system architecture consists in positioning a rotating shaft equipped with four rakes downstream the combustor, surrounded by hot gas flow. Exhaust gas sampling system, thermocouples, velocity and pressure sensors are directly mounted on these rakes. Displacement system is subjected to high level of thermal stress. Despite continuous water cooling, this configuration correctly ensures neither good sensors operation nor measurement accuracy.
A first study have been carried out by Topic leader in order to mitigate this dysfunction and the best solution to bypass these constraints seems to move gas sampling system and rotating system upstream the combustor. It implies to integrate the shaft to the air admission part. Study concludes that electrical motor that drives the shaft should be placed outside the system and data conveyors (sensors wires and gas sampling tube) must not disturb admission air flow.

The topic is to develop and work out a system corresponding to the above specifications.

Project Results:
In the framework of the period, AKIRA performed the design and the manufacturing of the module called ‘’NATIA’’ (for Nouvel Anneau Tournant Intégré Amont). It consists of two main parts: the mechanical module itself and the acquisition rack. The acquisition and the rakes displacement is controlled via a Labview software also developed by AKIRA for this purpose.

The mechanical module has been designed taking into account the following constraint

- Mechanical constraints linked to Akira’s solution environment are taken into account. Mechanical dimensioning will take into account the thermal gradient and thermal expansion differences of the materials used in order to avoid any tightening of the motion device. Stress analysis of the device will also be performed in accordance with Topic leader.

- Exhaust gases study requires velocity, temperatures and gas chemical species measurements. New system is fully adapted to existing module and is able to provide at least as much data as the previous one by using the same rakes to support sensors. Particular attention has been given to the shaft design in order to make it easily and rapidly fit with existing measurements rakes

- The electrical motor and associated encoder allowing continuous or step by step operation is placed outside the casing. The rotation is transmitted to the one-piece shaft tanks to a bevel gear. Pivot connection between casing and shaft is be obtained thanks to roller bearings. It is essential to take environmental conditions such as high temperature into account when choosing bearings and sealing rings.

- Holes are drilled through the shaft to hold sensors wires. The electrical rotating collector is gather thermocouples data. This configuration allows reducing thermal stress on components, but high combustor chamber temperature implies to protect collector (usual operating temperature 80-100°C) by an insulating ceramic layer and to cool it thanks to air circulation.

- Specific ducts are drilled/performed through the shaft as shown on the top scheme (See attached file). Rotating sealing rings allow various independent gas samplings.

- Inside system air cooling induces system intern pressurization. It is essential to take it into account when choosing bevel gears and designing sealing solutions. Shaft holes (or ducts) dedicated to house thermocouples are drilled wider to allow air admission.

- High temperature environment calls for particular cooling caution. Thermocouples are surrounded with hot exhaust gases and need to be permanently cooled by water flow. It implies ton create ducts/holes through the shaft to permit water circulation.

- Gases ducts are no longer than 400mm, there is no chance that gases samples temperature goes down from 1300°C below 190°C. A complete heating solution operating with hot oil circulation to maintain gas samples temperature between the casing and the gas analyser is implemented.

- Rotating rings ensure both water and gas circulations. Metallic rings ensure different static sealing. Rotating rings positioning need specific tools designed and provided by AKIRA.

Because all those constraints and the global complexity of the system, the development and manufacturing phase has been longer than initially planned. This extra duration is explained by different reasons:

The global technical complexity of the project has made our design operations slower than usual.
Other consequence of this complexity: we preferred to have every design evolution checked by TURBOMECA design department.
Difficulty to find machining companies able to machine such complex parts.

This extra duration leads AKIRA to request an amendment to the initial grant agreement, that has been released by the JU.

A complete control/command solution associated to AKIRA’s mechanical by AKIRA solution is designed, tuned and provided.
- A Labview based software is developped to perform both acquisition and automatic rakes displacement. It collects data from the test rig control unit (TURBOCAT) via FTP and gathers them to instantaneous data measured on the module trough the NATIA’s rack via an optical fibre. It also performs data post processing: statistical and frequency analysis as well as temperature calculation based on exhaust gas analysis.

- Hardware has been chosen according both Topic Leader requirements and data acquisition/generation needs. The data acquisition system allows collecting both direct data from thermocouples and processed one from gas analyser. A particular attention is given to gas analyser interface when designing the program architecture. The principal key points of the program, with respect to Topic Leader specifications, are:
+ Set in motion/actuators command.
+ Data collection, processing and recording (Topic Leader specified file format).
+ Risk mitigation software procedures (key parameters monitoring and associated alarms triggering).

At the end of the period, the complete system has been delivered, tested and validated by the topic leader. The system entirely fullfill the initial requirement and will be operated by the topic leader to improve the understanding of the combustors behavior, and so their efficiency.

Potential Impact:
The objective of this Topic was to design an experimental mean that improve the capability of analysis of the combustors manufacturers to understand combustors behavior. Based on this new device capability, developments and breaktroughs for the next generations of combustors will be accelerate, leadings to more fuel efficient and eco friendly engines.

List of Websites:

http://akira-technologies.fr/