Abstract
The article describes an assessment of possible changes in constant fatigue life of a medium flow-coefficient centrifugal compressor impeller subject to operation at close-to-surge point. Some aspects of duct acoustics are additionally analyzed. The experimental measurements at partial load are presented and are primarily used for validation of unidirectionally coupled fluid-structural numerical model. The model is based on unsteady finite-volume fluid-flow simulations and on finite-element transient structural analysis. The validation is followed by the model implementation to replicate the industry-scale loads with reasonably higher rotational speed and suction pressure. The approach demonstrates satisfactory accuracy in prediction of stage performance and unsteady flow field in vaneless diffuser. The latter is deduced from signal analysis relying on continuous wavelet transformations. On the other hand, it is found that the aerodynamic incidence losses at close-to-surge point are underpredicted. The structural simulation generates considerable amounts of numerical noise, which has to be separated prior to evaluation of fluid-induced dynamic strain. The main source of disturbance is defined as a stationary region of static pressure drop caused by flow contraction at volute tongue and leading to first engine-order excitation in rotating frame of reference. Eventually, it is concluded that the amplitude of excitation is too low to lead to any additional fatigue.
Highlights
The modern industrial process market is characterised by consistently restricting environmental and economic regulations [1]
The data from model tests should be used in next-generation units: directly, in designs based on similarity theory [3], or indirectly, through designs based on statistical semi-empirical mathematical models [4,5]
It is known that aerodynamically stable operational range of these centrifugal compressors will be limited by inception of “choking” in the vicinity of ṁ > ṁdes and by onset of “surging” at a certain point as ṁ < ṁdes [6]
Summary
The modern industrial process market is characterised by consistently restricting environmental and economic regulations [1]. Fulfilment of the second condition, requires the knowledge of dynamic stress at critical locations (primarily in impeller) as the machine interacts with unsteady flow structures Research in this field have been accomplished, but the amount of relevant data available in the literature is yet limited. The primary numerical campaign, concerns an operating condition at reasonably higher speed and suction pressure, which is done to reproduce the loads commonly met in industry. This part of the work is referred to as “model implementation”
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