The current work puts forth an implementation of a dynamic procedure to locally compute the value of the model constant C_DES, as used in the eddy simulation branch of Delayed Detached Eddy Simulation (DDES). Former DDES formulations [P. R. Spalart et al., “A new version of detached-eddy simulation, resistant to ambiguous grid densities,” Theor. Comput. Fluid Dyn. 20, 181 (2006); M. S. Gritskevich et al., “Development of DDES and IDDES formulations for the k- ω shear stress transport model,” Flow, Turbul. Combust. 88, 431 (2012)] are not conducive to the implementation of a dynamic procedure due to uncertainty as to what form the eddy viscosity expression takes in the eddy simulation branch. However, a recent, alternate formulation [K. R. Reddy et al., “A DDES model with a Smagorinsky-type eddy viscosity formulation and log-layer mismatch correction,” Int. J. Heat Fluid Flow 50, 103 (2014)] casts the eddy viscosity in a form that is similar to the Smagorinsky, LES (Large Eddy Simulation) sub-grid viscosity. The resemblance to the Smagorinsky model allows the implementation of a dynamic procedure similar to that of Lilly [D. K. Lilly, “A proposed modification of the Germano subgrid-scale closure method,” Phys. Fluids A 4, 633 (1992)]. A limiting function is proposed which constrains the computed value of C_DES, depending on the fineness of the grid and on the computed solution.

The basic question of whether a hybrid method for turbulence simulation can plausibly capture laminar-to-turbulent transition is addressed. The adaptive detached eddy simulation model (Yin & Durbin, Intl J. Heat Fluid Flow, vol. 62, 2016, pp. 499–509) does so. It dynamically adjusts a model constant, based on local mesh resolution and instantaneous flow features. In a laminar flow, the adaptive procedure returns zero subgrid viscosity, and large-scale low-frequency perturbations are resolved on the grid. However, rather than fully simulating transition, the hybrid model switches on at transition; small-scale turbulence is not resolved. It is found that the correct transitional behaviour is captured because the adaptive formulation responds to the initiation of small-scale components in the field of velocity gradient. The current work addresses flat-plate transition under the influence of free-stream turbulence and pressure gradient, encompassing bypass and separation-induced transition. First, the transition prediction mechanism of the adaptive model is explained. Then, the ability to predict transition statistically is evaluated, along with sensitivity studies of boundary conditions and mesh resolution.

The bevelled nozzle is a promising noise control approach and has been tested to suppress the noise levels in supersonic circular jets, but not in rectangular jets so far. In this study, implicit large-eddy simulations are performed to analyse the noise control of supersonic rectangular jets with single- and double-bevelled nozzles. Three nozzle pressure ratios ( $NPR = 2.3$ , 3.0 and 5.0) are considered to form two over-expanded cold jets and one under-expanded cold jet, exhausted from a baseline convergent–divergent rectangular nozzle with an aspect ratio of 2.0. Results show that, with the increase of $NPR$ , the oscillation of the jet plume is switched from a symmetrical mode to a flapping mode (preferential in the minor-axis plane), then to a helical mode, together with a reduction of the screech frequency. The amplitude of the screech tone is the strongest in the flapping jet, and the turbulent mixing noise is the most prominent in the helically oscillating jet. The single-bevelled nozzle induces asymmetric shock-cell structures and deflects the jet plumes, and the double-bevelled nozzle primarily enables the enhancement of the shear-layer mixing and shortens the lengths of the jet potential cores. With the bevelled nozzles, the gross thrusts of the baseline nozzle are increased by $0.05 \sim 7.38$ %. Details on the characteristics of far-field noise in the jets with/without the bevel cuts and their noise control mechanisms are discussed using the Ffowcs Williams–Hawkings acoustic analogy, dynamic mode decomposition and spatio-temporal Fourier transformation. Results suggest that the noise control has a close relationship with the destruction of well-organized coherent structures and the suppression of upstream-propagating guided-jet modes, which interrupt the feedback mechanism accounting for the generation of screech tones in the supersonic rectangular jets.

A 3D icing simulation code is developed in the open-source CFD toolbox OpenFOAM. A hybrid Cartesian/body-fitted meshing method is used to generate high-quality meshes around complex ice shapes. Steady-state 3D Reynolds-averaged Navier-Stokes (RANS) equations are solved to provide the ensemble-averaged flow around the airfoil. Considering the multi-scale nature of droplet size distribution, and more importantly, to represent the less uniform nature of the Super-cooled Large Droplets (SLD), two droplet tracking methods are realized: the Eulerian method is used to track the small-size droplets (below 50 $\mathsf{\mu }$m) for the sake of efficiency; the Lagrangian method with random sampling is used to track the large droplets (above 50 $\mathsf{\mu }$m); the heat transfer of the surface overflow is solved on a virtual surface mesh; the ice accumulation is estimated via the Myers model; finally, the final ice shape is predicted by time marching. Limited by the availability of experimental data, validations are performed on 3D simulations of 2D geometries using the Eulerian and Lagrangian methods, respectively. The code proves to be feasible and accurate enough in predicting ice shapes. Finally, an icing simulation result of the M6 wing is presented to illustrate the full 3D capability.