Accurate prediction of overall performance is vital if the extremely high design and development costs of modern high speed compressors are to be minimised. This fact, which is not novel, has led to the development of many computer programmes for such prediction. However, the most useful of these are proprietary. Some of those that are accessible in the open literature are of limited application to high performance axial compressors. This is mainly because they cannot reliably handle the transonic flows which characterise modern designs; nor are they generally easy to use from an interactive stand point. Accordingly, this report describes the origination of a streamline curvature programme for compressor performance prediction which attempts to bridge the gap in the existing literature base. The correlations used allow the package to be applied to more recent compressors at the highest level of the technology. In general, the programme is both interactive and fully modular. The former makes it easy for the user to access the programme quickly and effectively whilst the latter facilitates the use, for example, of alternative loss and deviation models to those prescribed within the programme. A further important feature of this new programme is its flexibility. For example, it can be used in three modes: firstly, as an analysis programme for performance prediction of compressors of known geometry; secondly, as a design/development tool to assess the likely performance changes occasioned by the introduction of geometrical variations in both blading and annulus shape; thirdly, as a straight design programme for new compressors provided a project analysis has been carried out beforehand. In the first two modes of operation, the programme requires details of standard blading, annulus geometry, design mass flow and pressure ratio. In the third, the user is free to prescribe his own blade shapes. The combined features described were introduced to make the package an ideal teaching tool. In this respect it should be emphasised that the complete novice to axial compressor design and performance assessment would experience difficulties using the package. However, the user who has some background, perhaps through lectures or in an appropriate industrial environment would quickly become adept. Against this background, whilst the programme is very interactive, it cannot claim, in its own right, to be an Expert System. The latter capability, however, can with some development easily be built in at a later stage. In order to minimise the time required accessing the programme, the report includes a comprehensive "user- guide". The validity of the prediction method is tested against an actual transonic compressor of known performance. The output is various and includes graphical presentation of all significant design/performance parameters throughout the compressor, including the compressor overall characteristic.

Abstract The application of Menter's transition model (Menter et al. (2004a), here-after known as the ץ - θ model) available in the CFX CFD code, for use within an axial compressor design group was studied. Simulations of a range of turbomachinery applicable test cases were undertaken, including a range of transitional flat plates and a 2D compressor cascade. Results were com¬pared to experimental data and the results of simulations performed with standard turbulence models. The ץ - θ model significantly improved the prediction of the boundary layer development, compared to the turbulence models. Comparisons with ex¬perimental data were also good. Features such as mid-chord transitional separation bubbles were predicted with the ץ - θ model, but not with the turbulence models. The ץ - θ model offered no consistent improved accuracy over the κ - ω SST turbulence model when predicting leading edge separa¬tion bubbles. The more accurate simulation of the boundary layer enables a closer prediction of viscous losses. 2D and 3D unsteady simulations of a low-speed axial compressor stator blade boundary layer, subject to impinging rotor wakes, were conducted. The pur¬pose was to determine the performance of the ץ - θ model in this environment, as there is no available literature for this. For both simulations, the model gave a good qualitative agreement to experimental data in the prediction of passing rotor wake effects on the suction surface. The effects on the pressure surface transition region due to wake passing were poorly predicted. All models were simulated on low and high-speed axial compressor stages. Results showed no improvement over the turbulence models of the ץ - θ model to predict blade exit parameters. The ץ - θ model does not present a significant enough improvement in the prediction of the flow to warrant its regular use in the design of axial compressor blading. However, it presents a useful tool in the development of high lift compressor blading.

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The high energy demand associated with open multi-deck refrigerated display cabinets is a direct consequence of their open design. The interaction between the cold refrigerated air inside the cabinet and the relatively warm air of the supermarket takes place across the air curtain, which serves as a non-physical barrier between the customers and the products. It has been estimated that 70% to 80% of the cabinet’s cooling load is due to ambient air infiltration into the cabinet refrigeration apparatus, which was previously entrained through the descending air curtain. A new generation of display cabinets has immerged in recent years, where the display-to-floor area has increased for the sake of maximizing sales. This modification leaves the air curtain with a larger display opening to seal against. Therefore, the design of such cabinets has now become more challenging, especially when attempting to ensure product integrity and temperature homogeneity while attempting to minimize their energy consumption. In this work, advanced numerical and experimental techniques have been integrated to quantify and also minimize the entrainment rate through the air curtain and the infiltration rate into open low-front refrigerated display cabinets. Experimentally, the Particle Image Velocimetry (PIV) technique has been used to map the velocity profile along the air curtain while the Infrared (IR) Thermography technique has been used to map the temperature profile across the cabinet. The Computational Fluid Dynamics (CFD) technique has been used in both case and parametric studies after confirming its validation with experiment. CFD was found to be a valuable tool for the simulation of open low-front refrigerated display cabinets, and the credibility of the results was assured when the boundary conditions were fine-tuned by experimental data. This thesis has demonstrated a systematic procedure where the entrainment rate through the air curtain can be quantified. The effect of various Discharge Air Grille (DAG) parameters was studied, and it was found that the entrainment rate is highly sensitive to the velocity profile and magnitude at the DAG. A velocity profile with a ramp shape having the maximum velocity near the cabinet yielded the minimum entrainment rate, hence the cabinet cooling load was reduced. In addition, two techniques were introduced for the determination of the infiltration rate of the cabinet. The first utilises the tracer-gas method to determine the specific amounts of ambient dry air and water vapour entering the evaporator coil, and the second uses psychrometrics to quantify the infiltration load as well as the other cooling load components by identifying the various heat transfer processes encountered during the operation of the cabinet. The ambient air infiltrated into the cabinet, although corresponds to 31% of the total mass flow rate, was found to be responsible for at least 85% of the total cooling load of the cabinet. This indicates that low-front cabinet suffer more from infiltration. The contribution of this work is by providing a better understanding towards the entrainment and infiltration processes related to open refrigerated display cabinets. The new techniques introduced in this work can help designers to better assess the impact of different design parameters and quantify the amounts of the entrainment and infiltration rates associated with open low-front refrigerated display cabinets.

Although the performance of twin screw compressors is heavily dependent on the rotor clearances within them, chamber models, used as design aids, allow for the specification of their magnitude and distribution but do not account for how these may vary during operation, as a result of internal temperature changes caused by the compression process. A validated procedure has therefore been developed to enable a chamber model to predict compressor performance, while including the effects of rotor and casing distortion resulting from dependant thermal effects. This has been achieved by the use of surface boundary mapping to calculate the rotor and casing temperature exposure within the compression chamber resulting from initial performance estimates. These detailed temperature distributions are processed analytically using appropriate assumptions that allow calculation of component temperatures and thermal growth. A program for calculation of leakage area curves has been adapted to support locally calculated variations in clearances. These updated area curves can then be fed back into the chamber model in an iterative procedure to simulate performance with thermally distorted clearances. The inclusion of thermal clearance corrections generally improved the accuracy of the chamber model when predictions from it were compared with test results over a wide range of operating pressures and temperatures. Furthermore, this work was found to be applicable in the evaluation of the interlobe clearance distribution between the rotors. Predicting clearance distortions and likely areas of rotor to rotor contact at a particular operating duty allows clearances to be optimised for the correct balance between performance and reliability; the results thus obtained were supported by findings from available test and tear down results.

Compressor plant frequently operates under unsteady conditions. This is due to pressure fluctuations, variable flow demand, or unsteady inlet conditions, as well as shaft speed variation. Also, following demand, compressor plants often work intermittently with frequent starts and stops. This may cause premature wear, decrease of compressor performance and even failure, which might cost millions of pounds to industry in downtime. However, there is still a lack of published data which describes intermittent plant behaviour, or predicts the effects of unsteady operation upon compressor plant performance. Thus, there appears to be a need to develop a mathematical model to calculate compressor plant performance during intermittent operating conditions and to verify this model with experimental data. Accordingly, this thesis describes an experimental and analytical study of screw compressor plant operating under unsteady conditions. For this purpose a one-dimensional model of the processes within a compressor was used, based on the differential equations of conservation of mass and energy, extended to include other plant components, such as storage tanks, control valves and connecting pipes. The model can simulate processes in both oil-free and oil-injected compressor plants during transient operation, including the effects of sudden changes in pressure, speed and valve area. Performance predictions obtained from the model gave good agreement with test results. This model can, therefore, be used to predict a variety of events, which may occur in everyday compressor plant operation.

The initial results of an investigation into the flow properties of a gaseous suspension of fine particles are reported. The objective of the work has been the acquisition of extensive experimental data, the analysis of which provides a better understanding of the pressure drop and flow characteristics of pneumatically transported solid particles. The versatility of the test rig is demonstrated by the diversity of the investigations performed during this study. Quantitative results were acquired for the flow of different-sized alumina particles flowing through vertical and horizontal pipes of different diameters, and around six bends of varying geometry. Dimensional analysis is profitably applied to the correlation of the experimental. data and the ensuing deductions examined critically. These conclusions were either substantiated or refuted by a visual appreciation of the nature of the flowing suspension. Investigations into bend erosion have explained the mechanism of the erosion process, and the data analysis has produced an equation which defines the mean wear rate as a function of the mean air velocity and the solids-to-air mixture ratio. This study has revealed the need for extensive study of topics not yet fully examined. Suggestions for further work are included at the end of Chapters 5, 6, 7 and 8.