Number of blades
Number of blades, stator outlet diameter and minimum blade distance are significant for the actual diffuser part of the stator and therefore have high influence on the flow losses. These 3 parameters have to be adjusted carefully.
The number of blades of impeller and stator has to be coordinated carefully in order to minimize pressure pulsation and therefore mechanical load and noise emission.
The number of impeller blades is defined and fixed by the impeller, otherwise it's an input value.
The number of stator blades can be modified and should be one of the recommended ones.
According to the number of blades z different pressure fields are generated in the impeller and the stator, which are moving relative to each other and are characterized by the periodicity p:
•impeller periodicity pI = νI∙zI
•stator periodicity pII = νII∙zII
The interference of both pressure fields cannot be calculated exactly. But most important for the resulting pressure field is the difference of both periodicities:
The following recommendations should be kept:
•m = 0 (impeller and stator blade count have shared integer multipliers) should be avoided in each case, because high pressure pulsation can be generated here.
•m = 1 should not be allowed in first and second order (νI=1; νI=2) due to unacceptable shaft vibration, if possible also in third order (νI=3).
•m = 2 as well represents a periodic impeller load, but is acceptable in most cases.
•Vibration modes with m >2 normally don't generate resonance and are allowed therefore.
For each modification of the stator blade count zII the m-values for each combination (νI = 1..3) and (νII = 1..3) are calculated and displayed in the table. Values m=0 are marked in red color, m=1 in orange and m=2 in yellow.
The recommended stator blade count according to the current number of impeller blades are represented below the input field.