CFD-CAA Method for Prediction of Pseudosound and Emitted Noise in Quadcopter Propeller

Subsonic flow air blade machines like UAV propellers generate intensive noise thus the prediction of acoustic impact, optimization of these machines in order to reduce the level of emitted noise is an urgent engineering task. Currently, the development of calculation methods for determining the amplitudes of pressure pulsations and noise characteristics by CFD-CAA methods is a necessary requirement for the development of computer-aided design methods for blade machines, where the determining factors are the accuracy and speed of calculations. The main objective is to provide industrial computer-aided design systems with a highly efficient domestic software to create optimal designs of UAV blade machines that provide a given level of pressure pulsations in the flow part and radiated noise. It comprises: 1) creation of a method for the numerical simulation of sound generation using the correct decomposition of the initial equations of hydrodynamics of a compressible medium and the selection of the source of sound waves in a three-dimensional definition, taking into account the rotation of blades and their interaction with the stator part of the UAV; 2) decomposition of the boundary conditions accounting pseudo-sound disturbances and the complex acoustic impedance at the boundaries of the computational domain 3) development of an effective SLAE solver for solving the acoustic-vortex equation in complex arithmetic (taking into account the boundary conditions in the form of complex acoustic impedance); 4) testing of a new method at all stages of development using experimental data on the generation of pressure pulsations and aerodynamic noise, including a propeller noise measurements.

Numerical and experimental evaluation of shock dividers

Mitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with different cross sections, allowing the shock waves to travel with different velocities along different paths. The separated shock waves redistribute the energy of the incident shock wave. The shock dynamics inside the divider are investigated using numerical simulations. A second-order dimensional split finite volume MUSCL-scheme is used to solve the compressible Euler equations. Furthermore, low-cost simulations are performed using geometrical shock dynamics to predict the shock wave propagation inside the divider. The numerical simulations are compared to high-speed schlieren images and time-resolved total pressure recording. For the latter, a high-frequency pressure probe is placed at the divider outlet, which is shown to resolve the transient total pressure during the shock passage. Moreover, the separation of the shock waves is investigated and found to grow as the divider duct width ratio increases. The numerical and experimental results allow for a better understanding of the dynamic evolution of the flow inside the divider and inform its capability to reduce the pressure pulsations at the exhaust of the pulse detonation combustor.

Numerical study of a case of the free discharge of water through the turbine with a braked runner

The paper presents a numerical study of the free discharge of water through the turbine with a braked runner. The simulation was carried out for a unit of a full-scale Francis turbine. The finite volume method was employed for unstructured meshes using the DES method. The simulation results show the flow structures, integral characteristics, and pressure pulsations in the flow path. The analysis of the applicability of this approach to real conditions is carried out.

Research of pressure pulsations during gas outlet to closed pipe area with liquid and installed disc barrier

A numerical simulation of the gas outflow to a closed region filled with liquid with a barrier disk was performed. The calculations were carried out using the VOF method, supplemented by the k-e turbulence model. Calculations were performed for three cases of 100, 200, and 300 mm distances of the disk from the injector with a gas outflow into water and liquid lead. The pulsations of axial pressure on a disk obstacle were investigated. It was found that the maximum pressure during pulsations of the upper gas volume in lead can be greater than the pressure in the gas receiver.

Intensification of mixing of fuel with supersonic air flow when injection and electric discharge are combined

This paper presents the results of experimental investigations of DC discharge influence on mixing intensification of transvers injected gas jet into supersonic aiflow. The air was used as injected gas to prevent the influence of chemical reactions on measurements. The data obtained during discharge includes current and voltage acquisition, registration of pressure pulsations in the jet downstream of discharge operation accompanied by correlation and Fourier analysis allowed to conclude that discharge significantly increase the pressure pulsations in a wide frequency range of 1000 Hz to 50kHz. Increase of the oscillations near the jet boundary is assumed to be related to kinematic mixing intensification of the injected gas with the oncoming flow.