Abstract.The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle) in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.

Для расчета параметров вибрации трубопроводов (амплитуды смещений, внутренних усилий и опорных реакций) разработаны модель, алгоритм и программа. Модель – квазиодномерная конечноэлементная система. Алгоритм расчета построен на базе метода парциальных откликов в его дискретном варианте. Выведены формулы для парциальных откликов и парциальных параметров, необходимые при реализации предложенного алгоритма. Влияние протекающей жидкости учтено приложением дополнительной инерционной нагрузки, которая, в свою очередь, учитывается коррекцией и модификацией инерционно-жесткостных характеристик модели трубопровода. В качестве примера рассмотрена задача о вибрации прямого трубопровода постоянного поперечного сечения, опирающегося на две опоры. Выполнено исследование влияния составляющих инерционной нагрузки на параметры вибрации, значения собственных частот и величину критической скорости жидкости. Оценена сходимость процесса в случае необходимости применения метода последовательных приближений. To analyze vibration parameters of the pipeline (displacement amplitudes, internal forces, and support reactions) the model, algorithm, and program were created. The model is a quasi-one-dimensional (quasi-1D) finite element system. The calculation algorithm is based on the discrete version of the partial responses method. Formulas for partial responses and partial parameters necessary for the implementation of the proposed algorithm were derived. The influence of the flowing liquid is compensated by applying an additional inertial load, which, in turn, is taken into account by correcting and modifying the inertia-stiffness characteristics of the pipeline model. The problem of the vibration of a straight pipeline of a constant cross-section with two points of support is given as an example. The influence of inertial load components on vibration parameters, own frequency values, and the critical velocity of the liquid were studied. The convergence of the process in case of using method of successive approximations was estimated.