Wind-turbine wakes over two-dimensional (2D) hills with different slope gradients are systematically investigated using large-eddy simulation with wind turbine parameterized as actuator disk model and hilly terrain modeled by immersed boundary method. The chosen hill models represent typical hilly terrains with and without flow recirculation in the wake of the hills. The flow characteristics of wind-turbine wakes [including mean velocity, wake-center trajectory, turbulence statistics, and mean kinetic energy (MKE) budgets] and the power performance are analyzed, and the related flow mechanisms are elucidated in our study. It is found that the velocity deficit in turbine wakes cannot be acceptably represented by the Gaussian model in the wake of the steep hill until at a further distance. It is also found that the assumption that the wake-center trajectory maintains a nearly constant elevation downwind of the hilltop proposed by Shamsoddin and Porté-Agel [“Wind turbine wakes over hills,” J. Fluid Mech. 855, 671–702 (2018)] may not be applicable in particular for the steep hill cases. Furthermore, the hilltop is the optimal location for turbine placement because the turbine harvests more wind energy due to the speed-up effect and suffers less fatigue loading due to the lower turbulence levels. Both the turbulence levels and the magnitude of vertical turbulent flux are found to drop below those of the flat ground case on the windward side of the hills, and they also decrease within the hill wake region compared with the no-turbine cases. A detailed analysis of MKE budgets reveals that the budgets of pressure transport and mean convection are mainly responsible for balancing the MKE in turbine wakes over hilly terrain.

The coastal region of China is exposed to severe typhoon threats and suffers significant casualties as well as economic losses due to seven to eight landed storms every year. This study developed a geographically weighted regression (GWR) circular subregion algorithm that considers the spatial variation characteristics of typhoon storms to map extreme-typhoon wind speeds. The continuously varying coefficient maps for typhoon-tracking, intensity, and wind field parameter recursive models are determined in the simulation domain using the best track data set from the Japan Meteorological Agency and geographically weighted regression. By introducing a genesis parameter model, each model module is validated independently or together by comparing the records in the best track data set in various circular subregions. The effects of the size of the circular subregion on the convergence of the typhoon wind hazard curve are investigated at two sites before an appropriate size is recommended. Extreme typhoon wind speeds of 10 coastal cities are modeled using the present model coupled with a well-developed analytical wind field model. Several factors that potentially contribute to the remarkable differences between this research and code suggestions as well as other studies are discussed. The estimated return period values of the annual maximum typhoon wind speed at 1,079 grid points in the coastal region of China are interpolated to achieve wind hazard contour maps. Several new findings regarding the spatial characteristics of extreme typhoon winds speed along the coastal region of China are examined.

We study the nonequilibrium dynamics of axionlike particles (ALP) coupled to Standard Model degrees of freedom in thermal equilibrium. The quantum master equation (QME) for the ALP reduced density matrix is derived to leading order in the coupling of the ALP to the thermal bath, but to all orders of the bath couplings to degrees of freedom within or beyond the Standard Model other than the ALP. The QME describes the damped oscillation dynamics of an initial misaligned ALP condensate, thermalization with the bath, decoherence, and entropy production within a unifying framework. The ALP energy density $\mathcal{E}(t)$ features two components: a “cold” component from the misaligned condensate and a “hot” component from thermalization with the bath, with $\mathcal{E}(t)={\mathcal{E}}_c{e}^{-\gamma (T)t}+{\mathcal{E}}_h(1-e^{-\gamma (T)t})$ thus providing a “mixed dark matter” scenario. Relaxation of the ALP condensate, thermalization, decoherence, and entropy production occur on similar timescales. An explicit example with ALP-photon coupling, valid post recombination yields a relaxation rate $\gamma (T)$ with a substantial enhancement from thermal emission and absorption. A misaligned condensate is decaying at least since recombination and on the same timescale thermalizing with the cosmic microwave background (CMB). Possible consequences for birefringence of the CMB and ALP contribution to the effective number of ultrarelativistic species and galaxy formation are discussed.