Search

We introduce an open-source and unified framework for transition analysis for laminar boundary layer natural transition at transonic conditions and over complex geometries, where surface irregularities may be present. Different computational tools are integrated in the framework, and therefore overcomes the difficulties of two separate and usually quite disparate processes when using $e^N$ method for transition analysis. To generate a baseflow with desired pressure distribution, appropriate pressure compatible inflow boundary condition needs to be developed and enforced. We first derive the system for 1D numerical stability analysis for boundary conditions, and construct three types of pressure compatible inflow. We demonstrate that the entropy-pressure compatible inflow is stable unlike other choices. Compared with the steady baseflow computation, the unsteady simulation for the disturbance field is more challenging for compressible flows because of complex wave reflections, which can easily contaminate the results. We therefore introduce the two main sources of wave decontamination and corresponding methods to obtain clean signal. The workflow within the framework is then verified by computing the disturbance development in 2D flat plate boundary layer flows at Mach $0.8$. The $N$-factors over a clean flat plate and a flat plate with a forward-facing step are generated, and agree well with the results from the reference. Following the verified workflow, We then analyze the disturbance growth on a wing section of the CRM-NLF model. The N-factor on a 2D simulation is generated and studied., Comment: 20 pages, 22 figures, presented at the 2022 AIAA Aviation Forum

One approach to reduce the cost to simulate transitional compressible boundary layer flow is to adopt a near body reduced domain with boundary conditions enforced to be compatible with a computationally cheaper 3D RANS simulation. In such an approach it is desirable to enforce a consistent pressure distribution which is not typically the case when using the standard Riemann inflow boundary condition. We revisit the Riemann problem adopted in many DG based high fidelity formulations. Through analysis of the 1D linearised Euler equations it is demonstrated that maintaining entropy compatibility with the RANS simulation is important for a stable solution. The maintenance of Riemann invariant at outflow leaves one condition that can be imposed at the inflow. Therefore the entropy-pressure enforcement is the only stable boundary condition to enforce a known pressure distribution. We further demonstrate that all the entropy compatible inflow Riemann boundary conditions are stable providing the invariant compatible Riemann outflow boundary condition is also respected. Although the entropy-pressure compatible Riemann inflow boundary condition is stable from the 1D analysis, 2D tests highlight divergence in the inviscid problem and neutrally stable wiggles in the velocity fields in viscous simulations around the stagnation point. A 2D analysis about a non-uniform baseflow assumption provides insight into this stability issue (ill-posedness) and motivate the use of a mix of inflow boundary conditions in this region of the flow. As a validation we apply the proposed boundary conditions to a reduced domain of a wing section normal to the leading-edge of the CRM-NLF model taken out of a full 3D RANS simulation at Mach 0.86 and a Reynolds number of 8.5 million. The results show that the entropy-pressure compatible Riemann inflow boundary condition leads to a good agreement in pressure distribution.

Unraveling a descriptor that is correlated with catalytic reactivity is essential for fast screening for the optimal catalysts for a given catalytic reaction. Herein, we propose bond-derived orbitalwise coordination number ($\overline{CN}^\alpha$, $\alpha$= $s$ or $d$) as a simple and accurate descriptor used for transition metal (TM) oxides that takes into account both geometrical and electronic structures around active sites, and avoids excessive computation burden. This descriptor has a strong scaling relation with the activity in oxygen electrochemistry, enabling us to readily screen for the optimal catalyst for $\beta$-MnO$_2$. $\beta$-MnO$_2$ with $\overline{CN}^\alpha$=5.6 by creating an oxygen vacancy on (110) surface exhibits the best oxygen electrochemical activity, which is well consistent with experimetal result. This descriptor can be universally applied to other TM oxides, e.g. RuO$_2$, opening up a new route as a guideline to design novel catalysts in catalytic reactions., Comment: This work is not completed!