A synthetic inflow generation method using the attached eddy hypothesis

The attached eddy hypothesis is used to develop a means of generating synthetic turbulent boundary layers. Fluctuating velocity fields are created from simple vortex shapes using the Biot-Savart law. These are superposed with mean velocity profiles from experiment or RANS to create boxes of data which can be fed in through the inflow plane of a simulation. This provides realistic time varying inflow data. The method is computationally inexpensive compared with other synthetic inflow generation methods. Two flows are investigated using this approach. In the first, detached eddy simulation is used to compute normal and angled injection of helium into supersonic turbulent crossflows at Mach numbers 3 and 4 respectively. The diameter of the injector in each case is comparable to the boundary layer thickness of the crossflow and it is to be expected that fluctuations in the turbulent boundary layer play an important role in the dynamics of the jet. A comparison of the helium mass fraction in the flow field is made with experimental data and the results are encouraging. The second case considered is a supersonic turbulent mixing layer with a convective Mach number of 0.46 and a Reynolds number of 12 × 10⁶/m (based on the velocity difference and average ρ and μ). The two streams are brought together across a thin splitter plate and the boundary layers on both sides are turbulent. Simulations are performed with steady inflow conditions and with the synthetic turbulent flow fields. The DES methodology is used for subgrid modelling and results are compared with the experiments of Goebel and Dutton. With unsteady inflow, the comparison with experiment was found to be very good.