Crossflow heat exchangers play a significant role in the operation of an aircraft's environmental control system (ECS). The bleed air supplied by an aircraft engine, at high pressure and high temperature, requires regulation and control in order to be used for various pneumatic services. In the present investigation, the transient temperature response of crossflow plate-and-fin ECS heat exchangers, having a large core capacity with both fluids unmixed, is investigated numerically and experimentally for perturbations experienced in temperature. A non-linear lumped model of crossflow heat exchangers with a state-space solution valid for equal fluid velocities is derived and evaluated, in terms of fluid placement and number of lumps (sections) required. Dependency of the heat transfer coefficient on flowrates is incorporated in the dynamic modelling of the heat exchanger. Two models are derived, and the variation of the mean exit temperatures of both fluids with time is compared for the two alternative models, with consideration of the number of transfer units and heat capacitance rate ratios. One model requires axial lumping of the primary surface alone, as done in most of the existing models, and the second involves incorporating the effect of secondary surfaces (fins) on the heat exchanger transient performance. To quantify the importance of modelling the fins, a comparison of both simulation models with experimentally obtained data from a physical model is presented. By including fins and complex non-linearities in modelling of the ECS heat exchangers, a precise representation of the heat exchanger dynamics and accurate temperature responses are predicted. The model developments reported in this article can lead to improved aircraft ECS design and optimization.
This paper presents Ansys Fluent laminar–turbulent transition results using the shear stress transport [Formula: see text] model applied to the workshop cases of the First American Institute of Aeronautics and Astronautics Computational Fluid Dynamics (CFD) Transition Modeling Prediction Workshop. The key objectives of this workshop were to assess the current state-of-the-art laminar–turbulent transition models in an industrial Computational Fluid Dynamics environment and to determine and document the best practices to simulate laminar–turbulent transition flows. Sensitivity of the shear stress transport [Formula: see text] model to mesh refinement was established on a zero-pressure-gradient flat plate. Two other cases [a two-dimensional natural laminar flow (NLF) (1)-0416F airfoil, and a scaled Common Research Model (CRM)-NLF aircraft model] were selected as validation cases using a hierarchy of structured and unstructured meshes. Due to the complexity of the geometry and the airflow around the Common Research Model (CRM)- Natural laminar Flow (NLF) aircraft model, mesh adaptation cycles were also conducted to capture the shock, the wake, and the wing-tip vortices produced by the CRM-NLF. The accuracy of the [Formula: see text] model is evaluated using transition location measurements obtained with temperature-sensitive paint, pressure coefficient distributions at multiple wingspan stations, and aerodynamic coefficients at numerous angles of attack. The outcome of these comparisons will provide guidelines to conduct laminar–turbulent transition simulations with the [Formula: see text] model on simple and complex aerospace designs.
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