Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 3 2021 05 22 Numerical Analysis of Cross Section Time Variation Effects of the Supersonic Exhaust Diffuser Numerical Analysis of Cross Section Time Variation Effects of the Supersonic Exhaust Diffuser 1469 1486 3807 10.22060/mej.2020.16956.6482 FA Nematollah Fouladi Space Transportation Research Institute, Iranian Space Research Center, Tehran, Iran 0000-0003-2737-0741 Mohsen Hataminasab School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran Sina Afkhami Space Transportation Research Institute, Iranian Space Research Center, Tehran, Iran Journal Article 2019 08 24 This paper is presented to investigate the deposition effect on a second throat exhaust diffuser performance. In the numerical simulation, the blockage of the diffuser due to the deposition of aluminum oxide is considered by a gradual and time-dependent cross-section constriction. In the initial conditions, the supersonic flow has been established in the nozzle and diffuser. Diffuser cross-section area is reduced by using a dynamic mesh method during the solution. The flow is considered compressible, viscous, and 2 dimensional axis-symmetric. The <em>k-ω</em> shear stress transport turbulence model is used to solve the turbulent flow field. Diffuser blockage (<em>n</em>) is equal to the ratio of instantaneous and primary diameters of the second-throat. By changing the value of <em>n</em> from 1 to 0.75, the onset of flow separation is moved to the downstream location in the diffuser. This results in a considerable reduction of total pressure loss and then improves the flow pressure recovery. Decreasing parameter <em>n</em> from 0.75 to 0.64, the flow structure is subjected to severe changes and the separation of the flow occurs near the diffuser inlet or inside the nozzle. In this condition, the diffuser state changes from starting to un-starting mode. Therefore, the vacuum condition vanishes in the test chamber. This paper is presented to investigate the deposition effect on a second throat exhaust diffuser performance. In the numerical simulation, the blockage of the diffuser due to the deposition of aluminum oxide is considered by a gradual and time-dependent cross-section constriction. In the initial conditions, the supersonic flow has been established in the nozzle and diffuser. Diffuser cross-section area is reduced by using a dynamic mesh method during the solution. The flow is considered compressible, viscous, and 2 dimensional axis-symmetric. The <em>k-ω</em> shear stress transport turbulence model is used to solve the turbulent flow field. Diffuser blockage (<em>n</em>) is equal to the ratio of instantaneous and primary diameters of the second-throat. By changing the value of <em>n</em> from 1 to 0.75, the onset of flow separation is moved to the downstream location in the diffuser. This results in a considerable reduction of total pressure loss and then improves the flow pressure recovery. Decreasing parameter <em>n</em> from 0.75 to 0.64, the flow structure is subjected to severe changes and the separation of the flow occurs near the diffuser inlet or inside the nozzle. In this condition, the diffuser state changes from starting to un-starting mode. Therefore, the vacuum condition vanishes in the test chamber. https://mej.aut.ac.ir/article_3807_43a115cbd6f4788924537365be3d6012.pdf