This paper describes the development and evaluation of a novel equivalent fluid circuit model capable of accurately predicting the performance of a load-type bi-stable supersonic fluidic oscillator. The model utilizes some aspects of previous models that are available in the literature. It is based on a quasi-steady assumption and includes a special non-linear element to account for certain aspects of the oscillator switching mechanism in addition to the traditional fluid resistance, capacitance, and inductance. A new technique for modelling a junction in a fluid duct network is also presented. Unlike previous studies which made use of empirical experimental data or analytical assumptions to estimate the fluid element parameter values and form of the non-linearity, the current method utilizes steady, computational fluid dynamic techniques to evaluate the parameters and non-linearity which cannot be accurately determined analytically. A simplification of the model is also used to establish the criteria for oscillations to exist. The transient solution of the model equations is then shown to give good quantitative agreement with previous experimental values of the oscillation frequency and amplitude. The model is also capable of predicting certain operational limitations and other trends in the data. Finally, the usefulness and robustness of the model are also demonstrated by showing the ease with which a parameter and design changes can be investigated.
Unique aspects in the development of bi-stable load-type fluidic oscillators that satisfy the requirement of producing large-amplitude pressure fluctuations during the charging of vessels for potential implementation in industrial processes such as the superplastic forming process are addressed in this paper. A Pseudo-3D computational fluid dynamic model is shown to be capable of accurately predicting the experimental values of the dimensionless frequencies and pressure fluctuation amplitudes as well as the experimental Schlieren images of the flow field obtained over a wide range of operating conditions. The Pseudo-3D model is also used to provide details of the fluid motion in the oscillator which could not be measured experimentally when investigating the operation of the device. The flow switching mechanism is identified as a consequence of a reduction of the flow deflection angle due to the increase of the downstream pressure load by the charging of feedback tanks. Some examples of the usefulness of the model as a cost-effective industrial design tool are also demonstrated. The effects of changing the number and size of the feedback tank volumes on the device frequency and amplitude of the oscillation are clearly shown using dimensionless variables.
Two-dimensional instead of three-dimensional computational fluid dynamic solutions of flow problems are quite often used in industry to facilitate short design turn-around times with varying degrees of success. A simple and robust approach for improving the accuracy of two-dimensional computational fluid dynamics solutions for problems involving internal flow passages in industrial applications is presented. The technique utilizes an approximation to the shearing stresses that act in the fully three-dimensional case but are ignored in the traditional two-dimensional approximation. Although the technique does not fully account for all the three-dimensional effects in such flows, it gives a reasonable estimate of the operation of devices with internal flows, even those involving transients. The usefulness and accuracy of the method are demonstrated through the application of the method to predict the performance of a supersonic fluidic oscillator for industrial design purposes. This brief provides industrial designers with a simple and robust tool for improving the accuracy of their computational fluid dynamic simulations.
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