CFD simulation of helicopter rotor flow based on unsteady actuator disk model

Actuator Disks(AD)can provide characterizations of rotor wakes while reducing computational expense associated with modeling the fully resolved blades.This work presents an unsteady actuator disk method based on surface circulation distribution combined with empirical data,blade element theory and rotor momentum theory.The nonuniform circulation distribution accounts for 3 D blade load effects,and in particular,tip loses.Numerical simulations were conducted for the isolated pressure sensitive paint model rotor blade in hover and forward flight using the HMB3 CFD solver of Glasgow University.Validation of CFD results in comparison with published numerical data was performed in hover,for a range of blade pitch angles using fully turbulent flow and the k-x SST model.In forward flight,the vortex structures predicted using the unsteady actuator disk model showed configurations similar to the ones obtained using fully resolved rotor blades.Despite the reduced grid cells number,the CFD results for AD models captured well the main vortical structures around the rotor disk in comparison to the fully resolved cases.

Validation of actuator disc circulation distribution for unsteady virtual blades model

The actuator disc method is an engineering approach to reduce computer resources in computational fluid dynamics(CFD)simulations of helicopter rotors or aeroplane propellers.Implementation of an actuator disc based on rotor circulation distribution allows for approximations to be made while reproducing the blade tip vortices.Radial circulation distributions can be formulated according to the nonuniform Heyson-Katzoff“typical load”in hover.In forward flight,the nonuniform disk models include“azimuthal”sin and cos terms to reproduce the blade cyclic motion.The azimuthal circulation distribution for a forward flight mode corresponds to trimmed conditions for the disk rolling and pitching moments.The amplitude of the cos harmonic is analysed and compared here with presented in references data and CFD simulations results.

Towards multi-fidelity simulation of flows around an underwater vehicle with appendages and propeller

Flow around a real-life underwater vehicle often happens at a high Reynolds number with flow structures at different scales from the boundary layer around a blade to that around the hull. This poses a great challenge for large-eddy simulation of an underwater vehicle aiming at resolving all relevant flow scales. In this work, we propose to model the hull with appendages using the immersed boundary method, and model the propeller using the actuator disk model without resolving the geometry of the blade. The proposed method is then applied to simulate the flow around Defense Advanced Research Projects Agency(DARPA) suboff. An overall acceptable agreement is obtained for the pressure and friction coefficients. Complex flow features are observed in the near wake of suboff. In the far wake, the core region is featured by a jet because of the actuator disk, surrounded by an annular region with velocity deficit due to the body of suboff.

Effects of a rooftop wind turbine on the dispersion of air pollutant behind a cube-shaped building

The concentration distribution of urban air pollutants is closely related to people’s health.As an important utilization form of urban wind power,rooftop wind turbines have been widely used in cities.The wake effect of the rooftop wind turbines will change the flow behind buildings and then affect the pollutant dispersion.To this end,the pollutant dispersion behind the building is studied via the computational fluid dynamics method.The actuator disk model and idealized cube are adopted to model the wind turbine and the building,respectively.The study shows that the rooftop wind turbine can reduce the pollutant mass fraction near the ground and the pedestrian level.Due to the wake effect of the rooftop wind turbine,the turbulent fluctuation behind the building is weakened,and the spanwise pollutant dispersion is suppressed.Besides,the rooftop wind turbine weakens the downwash movement of the building,which enhances the vertical pollutant dispersion.