The noise generated in the rotary compressor can be classified by pressure pulsation of the refrigerant and structural vibration. This paper deals with the noise generated by pressure pulsation of refrigerant in a rotary compressor. During the operation of the compressor, the refrigerant and the internal structure of the compressor have strong interaction with each other. At this time, the oil around the reed valve causes the compressor to overpressure the refrigerant, which is the main cause of noise generation. Therefore, the interaction between the refrigerant and the valve during the compressor operation is analyzed using the FSI technique. The pressure pulsation of the refrigerant and the behavior of the valve were analyzed. Also, the noise characteristics were confirmed through the spectrum analysis of the generated noise.

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SummaryThe main challenge of the immersed boundary approach is the proper enforcement of boundary conditions on the body interface without any spurious oscillations, which are induced by the nongrid‐conforming boundary configuration. In this study, a new sharp interface ghost‐cell immersed boundary method (IBM) is proposed for obtaining solutions near the immersed boundary with a high order of accuracy. The main idea is “jump‐reduction” instead of jump‐correction across the boundary interface by combining the ghost‐cell method with the flow reconstruction method. In the proposed IBM, the unknown values at the three points, that is, boundary points, ghost cell, and flow field reconstruction point are solved simultaneously using equations formulated by the moving least‐squares interpolation method. It is a hybrid of ghost‐cell and flow reconstruction methods, correlated with interface values, which result in a reduced jump‐discontinuity. In addition, a discontinuity‐distinguishing algorithm is introduced so that the low‐order method is applied only to the discontinuous or non smooth region, while the current high‐order method is applied elsewhere. Reduced jump‐discontinuity of the proposed IBM has been verified in both subsonic and supersonic flow using fundamental benchmark problems. We observed that the reduced jump‐discontinuity does not hamper the mass conservation and shows even better conservation property than conventional methods due to the nonoscillatory performance in smooth regions. The numerical results further confirm the ability of the proposed IBM to solve complex flow physics with high‐order accuracy and improved stability.

During a lift-off of a launch vehicle, a large amount of acoustic wave is generated by jet plumes. Acoustic waves lead to pressure fluctuations on the surface of the vehicle in the form of acoustic loads and these are transmitted to the internal payload. In order to evaluate the effects of acoustic loads, we developed the integrated simulation model. The model is mainly divided into two parts, prediction and reduction parts. First, the external acoustic loads are predicted empirically based on the Distributing Source Method-II (DSM-II) of NASA SP-8072. We developed the improved method able to consider the additional effects of surrounding structures. We perform a next prediction process for the internal acoustic environment by using Statistical Energy Analysis (SEA). For the Korean Sounding Rocket-III (KSR-III), we predict the internal acoustic environment and evaluate the stability of the payload in the fairing. After the prediction process, we perform the noise reduction simulation. With an active noise control (ANC) simulation, we could confirm the possibility and reliability of the noise reduction system.

This article proposes a hybrid adaptive mesh refinement (AMR) algorithm for the immersed boundary method (IBM) combination, and the AMR code is split into mesh and physics codes to optimize each part individually. The uniform parent grid solver is used for AMR grids by constructing hanging cells for the high‐order extension. The restrictive spatial refinement in a fully threaded tree (FTT) data structure is explored, and a simplified stencil search algorithm for hanging cells construction is introduced, including current and following child AMR level cells, if any. The proposed AMR method was applied to IBM, which offers flexibility in treating complex geometries in the Cartesian grid, leading to algorithmic simplicity and computational efficiency. Local near immersed boundary refinement is proposed to avoid complex and computationally expensive IBM and AMR algorithms near the solid bodies. Finally, a high‐order flux scheme extension at AMR level transition cells and the proposed method's applicability for steady and transient flows are demonstrated. Besides state and flux variables storage, the proposed hybrid AMR method's additional cost is 4.5 words/cell instead of 3.5 words/cell for 2D and 3.75 words/cell instead of 2.75 words/cell for 3D compared to the conventional FTT‐based AMR method. By comparing the uniform grid, the AMR final grid distribution shows that the optimal cell distribution based on flow physics reduces the cells required by more than 40% to resolve the complex flow features in less computational time. The enhanced performance and accuracy of the proposed AMR method in resolving different scale flow features are validated through benchmark problems.