الفهرس 
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Abstract
The design of suitable diffusers for various types of
turbomachines has faced, in the past and till now, many difficulties
which arose from the fac.t that no definite design
data is available to guide either investigators or designers.
The surne statement is also true in reg&rd to performance of
such diffusers.
In this research, a threefold trial was made to throw
some lleht on both the design and performance of diffusers
operating in a relatively low pressure ratio turbomachine.
The same impeller and measuring instruments were used in
all investigations.
The first trial was made to study the effect of number
of diffuser vanes on the performance of tne turbomachine.
For this purposet four diffusers were designed and constructed.
’l’hesehave 7,9,1 U and 12 vanes.
The results of these tests may be summarized as follows:
1. It was found that the number of diffuser vanes has
direct effects on the stage performance and diffuser
efficiecy.
2. The most efficient number of diffuser vanes aust be
choosen to optimize the diffusion advantage and blockage
effects.
). The changes in the gained pressure ratio and in diffuser
efficiency depend mainly on the ratio:
Overlap area between two successive vanes/No. of vanes
in the diffuser. The larger is this ratio, the minimum
is the combination of both friction and blockage effects
as compared to the efficient guidance of the flow through
the diffuser. This was obtained from the diffuser having
110 vane s ,
The second trial was made to show the effect of vane curv-
ature on such a performance. This was obtained by chOOSing
the most efficient diffuser of the first trial i.e. the diffuser
having 10 vanes.
’]he obtained results are:
1. It was noticed that diffuser vane curvature has also a
direct effect on the stage performance and diffuser
efficiency •2. By increasing the vane curvature, more overlap area
was obtained resulting in better performance and
efficiency. This result persists till the combination
of friction losses and secondary flow exceed the ad-
vantage of having a larger overlap area.
The third trial was made to clarify the effect of
diffuser rotation on the turbomachine stage performance.~
It was found that by rotating the diffuser, a higher pressure
ratio was obtained. This was also accompanied by a wider
range of mass flow rate.