On the aero-thermal performance of flat-plate film cooling hole with variable rib heights

Film cooling is widely adopted in the thermal protection of modern aerospace engines. The optimization of the film hole is an important issue in thermal designs. In this work, a density-based topology optimization is conducted to obtain a high-performance film cooling hole geometry. Unlike the traditional wall-temperature-based optimization objectives, a novel objective function based on the Q-criteria is proposed by taking the vorticity dynamics and flow mixing into account. Finally, a unique high-performance film hole is obtained, which shows superior performance compared to the standard cylindrical hole, particularly at high blowing ratios. The film cooling effectiveness can be elevated by 51 folds in the case of a high blowing ratio (M = 1.5). Analyses of the vortices and velocity fields suggest that the presence of the additional secondary vortex pair enhances the attachment of cooling air to the wall.

Topology optimization with vortex-intensity-based objective function enables novel film cooling hole with superior performance

Tang,

Zhu,

Tao

et al. 2024

Experimental investigations of aero-engine pre-swirl system performance improvement with consideration of inner seal flow effect

Zhang,

Liu,

et al. 2024

The pre-swirl system is essential for delivering cooling air to turbine blades within aviation engines. To explore the impact of the inner seal on the pre-swirl system, a high pressure ratio and high rotational speed experimental platform was constructed. The impact of inner seal inflow and outflow on the pre-swirl system's performance was evaluated. In response to the adverse effects of inner seal inflow on the system, a bypass structure was proposed to divert the inner seal flow, and the optimization effects and underlying mechanisms of the bypass structure were analyzed through a combination of experimental and numerical simulation approaches. The results indicate that the impact of inner seal outflow on the system is minimal, with the maximum variation in the temperature drop efficiency remaining below 1.9% under experimental conditions. Inner seal inflow, on the other hand, can have a significant negative impact on the system's performance. At a pressure ratio of 1.6, increasing inner seal inflow ratio leads to a decline in temperature drop efficiency from 0.55 to 0.43, representing a reduction of 21.8%. The bypass structure for inner seal can effectively prevent the mixing of inner seal flow with the mainstream within the pre-swirl cavity, reducing the pressure and temperature within the pre-swirl cavity. At a pressure ratio of 1.6 and inner seal inflow ratio of 15%, the specific work done by the airflow increased from 9.23 to 12.72 kW/(kg/s), increased by 37.8%, and the system temperature drop efficiency increased from 0.426 to 0.546, representing a 28.0% increase.

Dynamic characteristics and prediction and control models of subsonic exhaust from a container

Wang,

Hou

et al. 2024

This study combines experimental measurements, numerical simulations, and theoretical analysis to investigate the subsonic discharge process in a container under normal temperature and pressure conditions. Experimental data captured the internal pressure dynamics during exhaust at the atmospheric environmental pressure. Numerical simulations using OpenFOAM validated the isothermal exhaust model against the experimental results. Under the assumption of ideal gas and isothermal processes, a nonlinear differential equation was derived to describe the evolution of the container's internal pressure. This equation was simplified for a specific range of pressure ratios, yielding analytical solutions for the internal pressure of the container under both constant and variable external pressures. The effectiveness of the expressions of pressure inside the container was verified by comparing them with experimental and numerical simulation data. We further developed a formula for predicting exhaust mass flow rate, with a prediction error within 9%. An improved formula was subsequently proposed to reduce the error to below 0.4%, enhancing prediction accuracy. For containers with variable external pressure, a method for controlling the exhaust mass flow rate by predicting external pressure changes was proposed, demonstrating its effectiveness in achieving precise control.