Niclas Falck (2008). Axial Flow Compressor Mean Line Design
Erick Dick (2015). Fundamentals of
S.L Dixon (1998). Fluid mechanics and
Thermodynamics of fluid machines, 5th edition
To sum up,
the following flowchart is supposed to be
Mx1 is the axial
component of entry Mach number.
P denotes the passage
throat before the entry
the factors; maximum thickness to chord (t/c)
and the Axial Velocity Density Ratio, to apply a more advanced correlation as
2.3.2 Koch and Smith
factor according to Lieblein
Figure 4 Loss coefficient as a function
By establishment of the velocity
gradient on the suction side, in conjunction with results from cascade testing,
Lieblein deduced the following formulae for both diffusion factor and
equivalent diffusion ratio
2.3.1 Lieblein 1957 approach
2.3 Approach methods to Diffusion ratio and Diffusion
It’s defined as
2.2.4 Total pressure
It’s the ratio between the maximum velocity and the
2.2.3 Diffusion ratio
To calculate the diffusion factor there are various
approaches to which we are going to expose just before the procedure section.
Diffusion factor relates the maximum velocity at the
suction side of the rotor airfoil and the
velocity at the trailing edge as follows
It’s a dimensionless parameter which somehow indicates
the amount of loss due to flow, tells us
what the possibility for the blade to stall, primarily on the suction surface
of the airfoil.
2.2.2 Diffusion factor
Diffusers have a limiting property than nozzles from a
fluid-mechanics point of view, that it
can’t exceed a certain diverging angle to avoid high-pressure
gradient which in
turn facilitates stall, and since the exit velocity decreases as the pressure
increases, De Haller number is defined. Accordingly, from practical analysis, it was found that a safe
value of De Haller number should not be less than 72%.
It’s defined as the ratio between exit and inlet
velocities relative to the rotor.
related parameters to compressor losses
We are going to get into further details concerning
these two types, and their related parameters, the objective is to reach more
realistic fluid properties at the rotor exit for our design, worth to be
mentioned it’s constant-mean-diameter based.
represents the dominant source of loss, occurs near the end walls rather than
blades’ surfaces. It’s classified from the secondary losses due to the secondary crossflow
established by the curved path of the blade.
loss takes place as a result of boundary layer growth on the blade surface
On the other hand, from the Fluid mechanics’ perspective, those losses are distributed among
two major loss types
loss aspects through blades
As well as any flow circumstances, fluid flow through
a cascade of axial flow compressor experiences losses which are physically
dependent on various parameters like Tip
clearance, Aspect ratio, Solidity, Mach number& Reynolds number.
2. Axial flow compressor losses