Kenneth Ramsden

Ejector Pump Theory Applied to Gas Turbine Engine Performance inside Indoor Sea-Level Test Cell-Analytical and CFD Study

The paper deals with the interaction between the engine exhaust jets and the detuner of indoor gas turbine test facilities. This is part of an on-going research programme at Cranfield University looking at sea-level gas turbine testing from several aspects. In the case of sea level indoor testing several flow phenomena affecting both the engine performance and the thrust measurement arise inside the cell. Most of these phenomena are strictly related to the amount of secondary flow entering the cell which depends mainly on the interaction between the engine exhaust jets and the detuner. Following the above considerations this paper, beside a review of the main parameters that affect the performance of an ejector pump, concentrates on the development and application of an analytical ejector pump model. A complete description of the analytical model is presented including results obtained using genuine test data. The study covers the derivation of the Engine-Detuner ejector characteristic derived by using commercial CFD packages. Several computational models have been generated to analyze the influences of different Engine-Cell configurations on the performance characteristic of the ejector pump taking place inside indoor test cell. A comparison between analytical and CFD results is also presented.

Industrial Gas Turbine Performance: Compressor Fouling and On-Line Washing

Industrial gas turbines are susceptible to compressor fouling, which is the deposition and accretion of airborne particles or contaminants on the compressor blades. This paper demonstrates the blade aerodynamic effects of fouling through experimental compressor cascade tests and the accompanied engine performance degradation using turbomatch, an in-house gas turbine performance software. Similarly, on-line compressor washing is implemented taking into account typical operating conditions comparable with industry high pressure washing. The fouling study shows the changes in the individual stage maps of the compressor in this condition, the impact of degradation during part-load, influence of control variables, and the identification of key parameters to ascertain fouling levels. Applying demineralized water for 10 min, with a liquid-to-air ratio of 0.2%, the aerodynamic performance of the blade is shown to improve, however most of the cleaning effect occurred in the first 5 min. The most effectively washed part of the blade was the pressure side, in which most of the particles deposited during the accelerated fouling. The simulation of fouled and washed engine conditions indicates 30% recovery of the lost power due to washing.

Experimental Investigation of the Influence of Fouling on Compressor Cascade Characteristics and Implications for Gas Turbine Engine Performance

This article describes the findings of a study which examined the influence of fouling on the behaviour of a cascade and by making use of these results the performance implications for gas turbine engines of exposure to airborne foulants. A suction-type compressor cascade tunnel with a plenum chamber was employed for investigating fouling blade effects. The tests showed that such a testing arrangement allows the extraction of pressure and corrected velocity distribution data downstream of the blades that is comparable with what can be obtained from blow-type cascade tunnels. This study presents experimental results for smooth clean cascade blades and for uniformly fouled blades. For all the cases considered, mid-span-corrected velocity distributions and pressure losses taken one chord downstream of the blades were investigated in order to identify the effects of fouling on the blades. The result of fouling on exit flow angle was investigated as well. In the present study, cascade clean and fouled cases were used to predict real engine performance. Results are obtained in terms of stage polytropic efficiency, thermal efficiency, useful power, and compressor efficiency deterioration. Roughening the cascade blades uniformly with particles of 254 μ m size, the compressor efficiency dropped by 7.7 percentage points.

A Novel Method for Characterising Indoor Gas Turbine Test Facilities - Prediction and Control of Engine-Cell Performance

The paper deals with the characterisation of indoor gas turbine test facilities and is part of a field of research on going into Cranfield University looking at sea-level gas turbine testing from several aspects. In the case of gas turbine indoor tests, entrainment ratio ( = Wsecondary / Wprimary) represents one of the most important parameters and is usually applied to describe the performance of the engine-cell system. Basically, the secondary flow inside the cell alters the static pressure distribution around the metric assembly. Accordingly, the load measured by the load cells does not represent the real thrust delivered by the engine. At the same time, the presence of the secondary flow gives rise to several flow phenomena (distortion, separation, and recirculation), which can seriously affect both the performance and integrity of the engine. The paper deals with the characterisation of indoor gas turbine test facilities. In this context, the method proposed makes use of a previously developed ejector pump theory and of existing experimental data for deriving characteristic and operating enginecell lines. Two matching procedures are established using such lines which are shown to be able to predict and control respectively. Furthermore, both an analytical and experimental approach to quantify the effects of different engine-cell configurations are also presented and discussed. Though the importance of understanding and optimising the cell entrainment ratio is widely recognised no such a work has been found in the open literature. Accordingly, the novel method presented along with this paper can be of immediate benefit to the operator of enclosed gas turbine test cell facilities.

CFD Predictions of Cascade Pressure Losses Due to Compressor Fouling

The performance of the compressor component of an industrial gas turbine can suffer seriously from fouling due to the ingestion of particulate matter like sand and dust. In particular, in very hostile environments when mixed with oil vapour, the outcome is a substantial loss in power and efficiency due to compressor fouling. To recover this performance loss and subject to manufacturer’s firing temperature limitations, the engine fuel flow could be increased. This in turn would reduce the creep life of the turbine blades and result in large increases in engine operating costs. These effects can be reduced markedly by keeping the compressor as clean as possible through a combination of intake filtration and compressor washing. Against this background, the ongoing research involves the design and commissioning of a 2-D cascade tunnel to facilitate estimation of pressure losses and associated compressor inefficiencies as a function of degree of fouling (surface roughness). This paper presents preliminary CFD predictions for smooth clean cascade blades and for fouled blades applying on them different levels of fouling. For all these cases, velocity distributions and exit flow angles one chord downstream of the blades towards the cascade flow stramtube at a midspan height have been investigated. Also the pressure losses associated are presented. All these CFD results will be used to complement the future experimental measurements not yet obtained, which will be undertaken at different fouling level and blade washing scheme as well.Copyright

A Comparison of Loss Models Using Different Radial Distribution of Loss in an Axial Turbine Streamline Curvature Program

The streamline computer codes published in the open literature and used to analyze the performance of axial flow turbines have employed a particular loss model chosen from a number of existing prediction methods. It is well known that the performance prediction methods developed for one-dimensional models concentrates the losses at the blade mid-height. When used in a streamline curvature model, however it is necessary to distribute these losses along the blade span. However the way to distribute the losses is not unique, as is clear from the open literature. Some methods seem to be an arbitrary procedure, with a shortcoming in representing the real flow behavior within the blade row. In this paper, two different loss distribution models were implemented in a streamline curvature program specially developed for the study of axial flow turbine performance. The study seeks to establish which one best represents the reality of the complex flow physics occurring within a blade row. Three different loss models were also implemented in the program to check their reliability and validity when combined with different loss distribution systems. Performance maps for a single-stage turbine were generated by means of different combinations of loss models and radial loss distributions. The computed result for each case was compared with available experimental data of a single-stage turbine.Copyright

Prandtl—Meyer Expansion

This table of Prandtl—Meyer Angle as a function of Mach Number is calculated from the single equation:

Performance and Techno-Economic Investigation of On-Wing Compressor Wash for a Short-Range Aero Engine

{\rm{Prandtl - Meyer}}\;{\rm{Angle = }}\sqrt {\left( {{{\gamma + 1} \over {\gamma - 1}}} \right)} {\tan ^{ - 1}}\sqrt {\left\{ {{{\gamma - 1} \over {\gamma + 1}}({M^2} - 1)} \right\}} {\tan ^{ - 1}}\sqrt {({M^2} - 1)} ({\rm{radians}})