One final menu option exists at the top menu bar of LURC. By clicking on the button About a very brief introduction to the program and the different design tools appears, see figure 8.31. This serves as a quick start guide to LURC, and is by no means exhaustive.
Figure 8.30: The geometry result of the wedge diffuser analysis. To the left are the trajectory within the vaneless space shown, along with all wedges characterizing the diffuser. To the right are the hub and shroud contours of the diffuser shown.
Figure 8.31: The About-view in LURC. This part of the program gives quick background information and some guidance to the different design tools
Chapter 9
Conclusions
This final part of the report gives some concluding remarks, mainly referring to the questions given in section 1.3. Also, potential improvement areas of the analyses are brought up.
9.1
Questions answered
The first question that was to be answered were how to model the impeller in a quick and efficient manner. This question has been answered in chapter 3 and 4 where two different models were outlined. Although both models are one-dimensional, they have been implemented in two separate ways. The preliminary impeller analysis provide a very fast mean to find an impeller geometry and performance. Since many of the important parameters, such as impeller internal efficiency, are determined completely within the analysis the results can be assumed rather reasonable. The detailed impeller analyses is also a very fast tool, but will require some knowledge of the user when selecting design data. It is not impossible at all to use this tool and find an internal impeller efficiency above 1. Thus, this tool require, to a larger extent, critical evaluation of the results calculated. Also, since the geometry of the impeller may be determined completely by the designer it gives a huge freedom of design choices. However, it again requires wise choices of the designer to get results applicable in practice. Nevertheless, both models can with no doubt be regarded as both quick and efficient giving the first question in section 1.3 two answers.
To answer the second question, if there is a method to study the impeller in a more thorough way, the answer is simply yes. To dig a little deeper, chapter 5 gives the full length answer, describing a type of analysis having found broad application within the turbomachinery field. Streamline curvature methods are widely accepted throughout the industry, see for instance Casey and Robinson (2008). This method must also be regarded very quick and efficient, giving the designer an idea of the velocity distribution in matter of tenths of a second. The quasi three-dimensional flow analyses implemented is based on the detailed impeller design and any changes found necessary in the internal flow analysis is easily changed using the detailed impeller analysis tool.
The third question found in section 1.3 related to the vaneless diffuser; how can an analysis method for these components be found? The answer is given in chapter 6. Here, a model taking not only compressible effects but also the phenomena of wall friction into account has been employed. Using this type of model is an improvement compared to the very simple constant angular momentum theory. Although the use of a friction factor can by no means model all phenomena encountered in a vaneless diffuser, it serves as a convenient and efficient way to
incorporate deviations from constant angular momentum behaviour. Further, the computer implementation allows a varying friction factor along the fluid path, giving the designer an extra degree of freedom when analysing a vaneless diffuser.
Finally, the last question, in what way a vaned diffuser can be modelled, is answered throughout chapter 7. In this work, the analysis was focused towards channel diffusers of the wedge type. Since all vaned diffusers contain some amount of vaneless space, the theory of vaneless diffusers was again applied to this part of the diffuser. Within the channels compressible channel flow theory was applied, again making use of the friction factor concept. Using the one-dimensional methods for modelling diffusers gives rise to fast solutions and reasonable result of the expected performance levels. However, the flow leaving the impeller is everything but one dimensional, something any designer must keep in mind.
Looking at the computer program in general, it is a rather straight forward design suite, enabling the designer to quickly change what design tool to use. Also, many of the different analyses are interconnected, enabling results from one module to be used in another. Using computers of current standard, solving problems in any of the design tools takes no longer than a few seconds. The program thus fulfil the main objective; being a fast and efficient computer program, taking many different aspects of the compressor into account. Also, a lot of effort have been put in to make LURC as easy and intuitive as possible to use. One of the intentions has been to allow any engineer interested in radial turbomachinery to use the program, regardless of what knowledge level he or she has.