Relationship between turbine blading friction and vacuum
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I’ve seen a statement saying that a certain level of vacuum is required before starting up, and one of the functions of this vacuum is to reduce fan friction. How should we understand the relationship between fan friction and vacuum?
Blowing friction generates heat, which raises the exhaust temperature; a certain degree of vacuum can lower the exhaust temperature.
During single-unit tests of the turbine, the exhaust temperature is generally higher than during normal operation. The main reason for this is insufficient air intake, which results in inadequate driving force for the gas flow; the heat generated by friction from the blower further increases the exhaust temperature. You can understand it by looking at the relationship between exhaust temperature and intake air flow. Temperature is directly related to the degree of vacuum.
During the individual testing of a turbine, when the volume of air is low and the angle between the airflow and the tangent to the blades is large, friction occurs, resulting in heat generation.