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Analiza niestacjonarnych zjawisk przepływowych w przewodach zasilanych pulsacyjnie

Olczyk A.

Zeszyty Naukowe. Rozprawy Naukowe / Politechnika Łódzka

2009

Z. 360

9-152

The phenomena occurring in a pulsating flow of gas through the straight pipe of a circular cross-section have been analyzed in this dissertation. Measurement methods that allow for determination of unsteady flow parameters (pressures, velocities and temperatures) for the pulse frequency up to /=200 Hz have been applied and improved. A method that enables to distinguish two components of the measured temperature signal, corresponding to static and dynamic temperature, has been proposed as well. In order to analyze the observed unsteady phenomena, a Bannister wave model that enables the pressure signal decomposition into the incoming and reflected wave has been adapted. Due to the employment of this model, the flow behavior in the types of systems under investigation could be explained to a great extent. A trial to adapt the classical acoustic theory to pulsating flow conditions has also been undertaken in the dissertation. The resonance frequencies of the systems under consideration have been determined with this method and a very good convergence of the calculation and measurement results has been obtained. The amplification coefficients for pressures and specific mass flow rates defined in the study reach their maximum values for the theoretically determined resonance frequencies. It has been also found that the pipe supplied with a pulsating flow can be treated dynamically as an object of the second order, which is confirmed by the amplitude and phase characteristics determined experimentally. To widen our knowledge on the character of flow parameter dynamics in the analyzed measurement cross-sections, unsteady temperature and specific mass flow rate fields have been measured for some selected conditions of excitation. It has been found that the pulsating flow alters the shape of the specific mass flow rate profile, leading to its uniformity. In the case of temperature, we encounter a very high degree of homogeneity of the unsteady fields recorded at the pipe inlet, which also indicates indirectly the homogeneity of static pressure fields. As regards practical applications of these investigation results, apart from typical cases of a flow through inlet and outlet pipes of diesel engines and piston compressors, they can be employed in all installations where a pulsating flow occurs and phenomena such as an increased pulsating amplitude or a reverse flow cause disturbances in their correct operation.