The effect of blade sweep has been studied numerically with the Lattice Boltzmann Method on a family of low-speed free-vortex axial fans with sweeps of ±45°. Good overall aerodynamic agreement is first demonstrated on all fans at the design condition, particularly in the tip gap. The local larger wall-pressure fluctuations seen in the unswept and backward swept fans compared to the forward case are traced to the stronger tip vortices that remain in the rotational plane or even move upstream. These stronger and faster vortices interacting with the fan blades are then responsible for the larger noise levels observed in the acoustic spectra of these fans, and particularly for large subharmonic humps. Excellent agreement between experimental and numerical noise predictions is finally reported stressing the dominant tip noise.

Two blade curvatures representative of those found in automotive fans are compared. Measured performances are analyzed for forward and backward curved blades, either with or without heat-exchangers placed in front of them. The backward fan demonstrated good efficiency but poor acoustics, whereas it is the contrary for the forward fan. Investigations are completed by a numerical analysis of the flow in the cooling module. Different integration effects are highlighted depending on the blade curvature, showing variation in pressure, torque and efficiency. Analyses of blade loadings show that the flow is more homogeneous with a forward curved fan and it produces less unsteadiness at the blade tip. Post-processing of detached eddy simulations (DES) shows density fluctuations on the blade wall and confirms the correlation between the large vortical structures and the acoustic sources for both fans. In addition, with the forward fan, the sound propagation is less directed towards the axis of rotation and it yields up to −3.6 dB of sound pressure level (SPL) measured in front of the cooling module. As a conclusion, any choice for a fan must result from a compromise between aerodynamics and aeroacoustics, and the final performances must be carefully checked on the module.

The aim of this paper is to provide data on the influence of the geometry of the fins on the acceleration performance of a ram accelerator projectile in the subdetonative mode. The data that are presented in this paper are derived from a non reacting computation performed at the French Research Institute (ISL) with the commercial numerical code TascFlowTM from AEA Technology. This code calculates the pressure and temperature profiles in a non-reactive flow around the ram accelerator projectile. Three types of projectiles were studied with respectively three, four and five fins. Furthermore, different fin geometries were studied. The wall temperature behavior was investigated, in order to explain the high erosion of the projectile that is observed as the projectile comes out of the tube. Moreover, the high temperatures that were derived from the calculation explain the initiation process of the reactive at some point of the projectile, which, in turn, explains the unstart process. These calculations were conducted during ram accelerator operations at ISL and were used to explain some effects observed on the experimental data obtained in both the 30-mm and 90-mm caliber facilities.

A large variety of initiation results in a ram accelerator have shown that a series of interactive parameters play a key role, such as the design of the facility, tube diameter, shape of both the projectile and sabot and the choice of the reactive propellant mixture. Two different ram accelerators were used at ISL for this study, namely a 30-mm and a 90-mm-caliber. In addition to the diameter effect, it was observed that the dimension of the sabot must be adapted not only to the caliber of the tube but also to both the launching device and vent section that are located before the ram accelerator tube. For instance, a sensitive mixture yielded a superdetonative mode in the larger tube diameter facility at ISL. Comparative experiments were conducted in these two caliber ram accelerators at ISL. Important transient effects were observed as the projectile enters the tube which could explain the discrepancies between the data derived from similar devices. The aim of the present paper is to provide a series of data that show the effect of the tube diameter on the initiation process of the propellant mixtures that are currently used in this facility. The design of the sabot is also discussed.

The global exploring feature of the surrogate model makes it a useful intermedia for design optimization. The accuracy of the surrogate model is closely related with the efficiency of optima-search. The cokriging approach described in present studies can significantly improve the surrogate model accuracy and cut down the turnaround time spent on the modeling process. Compared to the universal Kriging method, the cokriging method interpolates not only the sampling data, but also on their associated derivatives. However, the derivatives, especially high order ones, are too computationally costly to be easily affordable, forming a bottleneck for the application of derivative enhanced methods. Based on the sensitivity analysis of Navier–Stokes equations, current study introduces a low-cost method to compute the high-order derivatives, making high order derivatives enhanced cokriging modeling practically achievable. For a methodological illustration, second-order derivatives of regression model and correlation models are proposed. A second-order derivative enhanced cokriging model-based optimization tool was developed and tested on the optimal design of an automotive engine cooling fan. This approach improves the modern optimal design efficiency and proposes a novel direction for the large scale optimization problems.