The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct. Multiple shock waves are formed inside the duct at a shock Mach number of 1.75. The duct has an exit height of H, and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H, 50H, and 150H. The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves. The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure, shock train leading-edge location, shock train length, and the size of the separation bubble. The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition. The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted. The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations. The RMS amplitude of the normalized shock train length (ζ_ST) increases with an increase in the exit duct length for the self-excited oscillation condition. When the downstream perturbation frequency is increased, ζ_ST is decreased for exit duct configurations. For all exit duct designs and downstream forcing frequencies, the size of the separation bubble grows and shrinks during the shock oscillations, demonstrating the dependence on duct resonance and forced oscillations.

A pair of unidirectional turbines (UT) can operate in oscillatory airflow without additional units. However, this arrangement suffers from poor flow rectification. A fluidic diode (FD) offers variable hydrodynamic resistance based on the flow direction, and this can be coupled with UT to improve flow rectification. In this work, a numerical investigation on the effect of FD with UT is presented using the commercial fluid dynamics software ANSYS Fluent 16.1 with k-ω SST turbulence closure model. Periodic domains of UT and FD are numerically validated individually with experimental results. Later, both are coupled to obtain the combined effect, and these results are compared with the analytical approach. It was observed that coupling FD with UT improved the unit’s performance at the lower flow coefficient (<1), but its performance decreased as the flow coefficient increased. Due to the diode’s presence, fluid leaving the turbine experiences higher resistance at a higher flow coefficient, which decreases the overall performance of the combined unit.

Flow around a pair of flat plates is a basic hydrodynamics problem. In this paper, the flow and heat transfer characteristics of two parallel plates with different edge shapes are numerically calculated. Under different inclined angles, the influence of chamfered and rounded structures with different sizes at the end-edge on unsteady flow and heat transfer characteristics of two parallel plates are analyzed. It is found that the instability and unsteadiness of flow decrease with the increase of end-edge size, and the non-uniformity of wake velocity of both rounded and chamfered plates decreases gradually. The non-uniformity of wake temperature increases firstly and then decreases at a small inclined angle, and the amplitude becomes the largest when S_rou(S_cha)=3, while it basically keeps monotonically increasing at a large inclined angle. Moreover, the global heat transfer performance of the flat plate is obviously affected by the end-edge modification, especially the chamfered structure. With the increase of chamfered size, the global Nusselt number basically shows the decreasing trend. This study provides a theoretical basis for the application of plate-shape structure in engineering fields.

Hot gas ingestion refers to the phenomenon of mainstream hot gas flowing into the space cavity of a turbine wheel. Previous studies have found that mainstream annulus pressure distribution plays an important role in hot gas ingestion, but due to its complexity, the mechanism of the interaction between mainstream flow and hot gas ingestion remains unclear. This paper adopts the URANS method, and three sealing flow rates are considered, named C_w=0, C_w=500, and C_w=5000. The time-averaged annulus pressure distribution shows that an increase in the sealing flow decreases the pressure value, and the effects of the sealing flow on the pressure distribution of the leading edge of the blade are much more influential than that of the trailing edge of the vane. The unsteady pressure time-space distribution in the annulus indicates that a time-space tilted distribution of pressure at the rim exits when the sealing flow exists. This phenomenon is mainly due to the strong feedback mechanism of the sealing flow to the annulus pressure field. A comparison of the pressure and mean radial velocity distribution of the mainstream shows that the ingestion mainly occurs on the blade side, where the pressure is lower than on the vane side. The flow characteristics at the wheel rim are analyzed with a sealing flow rate C_w=5000, and under these conditions, both pressure-induced ingestion and ingestion caused by a passage vortex can be inferred. The three-dimensional and inertial effects of the mainstream at the wheel rim lead to the generation of separation vortices on the blade side, and the presence of separation vortices leads to ingestion along the blade side. At the same time, pressure on the blade side will cause the fluid to have a radial inward flow tendency, which will promote the formation of separation vortices, leading to more serious ingestion in the high-pressure region on the blade side. The blade pressure field can be more significant than the vane trailing pressure field in the rim seal ingestion, and it contributes some explanations to the open question: the effect of blade on ingestion.