On a centrifugal compressor test facility various experimental investigations have been carried out contributing a valuable gain in knowledge on the fundamental flow physics within passage type diffusers. An extensive measurement series using various steady, unsteady and laser optical measurement techniques has been performed to detect the unsteady, highly three dimensional diffuser flow under various realistic operating conditions. Zachau et al. [1] presented the test facility and the results gathered under nominal conditions. As a follow-up the results of investigated parameter variations are now presented, covering bleed variations, impeller tip clearance and impeller-diffuser misalignment studies. The data is compared to the benchmark created from the nominal baseline data sets and evaluated with respect to the compressor stage performance. Zachau et al. [1] found that under nominal conditions the flow in the pipe diffuser separates on the pressure side in the first half of the pipe. In the last 30% of the pipe hardly any deceleration of the flow takes place. From this, special attention is given to the investigated parameter variations regarding a first proposal for a diffuser design change, which consists in shortening the diffuser. The results for each parameter variation are evaluated in detail in direct comparison to the nominal baseline configuration underlining the conclusion made earlier that the diffuser flow always separates on the pressure side with negligible deceleration in the last third of the diffusing pipe.

Centrifugal compressor stages with pipe diffusers are considered to perform with high efficiency. Yet very little information on these kinds of diffusers is available to this day. Therefore, experimental investigations have been performed on a centrifugal compressor stage with a pipe diffuser. An extensive measurement series using various steady, unsteady and laser optical measurement techniques has been performed to detect the highly three dimensional diffuser flow and create a benchmark for further development steps. Whereas this paper presents the test rig and the results gathered under nominal conditions, in a follow-up paper the results of the parameter variation studies covering bleed variation, impeller tip clearance and impeller-diffuser misalignment are compared to the nominal baseline and evaluated with respect to the compressor stage performance. For the investigations performed under nominal conditions it was found that the diffuser flow separates on the pressure side in the first half of the pipe. In the last 30% of the pipe hardly any deceleration of the flow takes place. From this, special attention is drawn to the parameter variations regarding a first proposal for a diffuser design change, which consists in shortening the diffuser. Ongoing investigations cover this design proposal. Along with the results of the ongoing investigations, the numerical investigations accompanying the experimental work will also be presented in follow-up papers.

The current maintenance and overhaul of large civil jet engines is completely based on-condition and is widely customized to the individual requirements of the operation. Therefore, a very important factor for an effective and economic engine maintenance program is the investigation and appreciation of the current engine condition, as well as its individual deterioration mechanism. This paper is introducing a method to analyze the engine performance deterioration between two typical off-wing maintenance events (shop visits) so as to draw conclusions for maintenance planning and operation. In order to perform a precise evaluation the performance analysis is conducted on a modular level. Therefore the engine is divided into the following major modules: FAN, LPC, HPC, combustor, HPT, LPT and exhaust nozzle. The basis for the evaluation is the overhauled engine condition after a shop visit (pass-off test run) and the deteriorated engine condition after operation (incoming test run). These two points in the engine life cycle provide specific engine conditions that are to be analyzed by scientific and commercial software, and combined with a self-developed engine performance model in order to obtain the desired results: The individual engine deterioration during operation demonstrated by the differences of the modular performance between incoming test run and the last pass-off test run. In addition, to ensure the continuous monitoring of the performance status between the two test runs, it is important to analyze the “on-wing operation”. This is done using MTU’s Engine Trend Monitoring (ETM) system, which generates performance data based on the available in-flight data. In this paper an analysis example is used to present the analytic method and the obtained results. Reasons of deterioration are evaluated separately in reference to different environmental influences from specific geographical regions. In summary this paper introduces a solution to track the total engine performance based on modular evaluation values, starting at improvements for pass-off and incoming test runs as well as performance degradation during the on-wing time.