Analysis of flow characteristics and cooling performance of a novel impingement/effusion structure with bypass hollow holes

Thermal protection is a crucial issue for a long-flying hypersonic aircraft. In this work, a composite cooling method is proposed and implemented on a hypersonic blunt cone. The composite cooling method combines impinging and convective cooling at the cone head with transpiration cooling employed downstream to produce an overall cooling effect of the cone. Using computational fluid dynamics, the influences of the cooling gas and different attack angles on the cooling effect are examined. The results indicate that the combined cooling method can effectively reduce the overall outer wall temperature of the cone. In particular, with the combined cooling method, an increase in mass flow rate of the cooling gas has been observed in numerical tests, which results in a decrease in the head temperature. The maximum temperature decrease can reach 77.0% on the wall when the mass flow rate of the cooling stream is 1.1 kg/m2 s. The cooling performance on the leeward side can be better than that on the windward side for a fixed cooling gas mass flow rate. This gap in cooling performance between the two sides can be further amplified by a larger attack angle. Quantitatively, when using the combined cooling method, the temperature difference between the windward and leeward sides increases from 106 to 270 K when the attack angle increases from 4° to 8°. The numerical results in this study could provide theoretical and statistical guidance for the design of novel active thermal protection methods for hypersonic aircraft.

Numerical study of a composite cooling method for hypersonic aircraft

Chen,

Tian,

2024

Experimental and numerical studies on multi-jet impingement flow characteristics in a double-wall structure under rotating conditions

You,

Liu,

et al. 2024

This study employs time-resolved particle image velocimetry technology to investigate the flow field characteristics of a double-wall jet structure under both stationary and rotating conditions. The jet rotation number range from 0 to 0.08, covering both clockwise and counterclockwise rotations, with a jet Reynolds number of 4000. The dimensionless jet-to-target spacing is 2. In order to elucidate the flow mechanisms based on experimental results and provide complementary insight, validated numerical simulations under conditions identical to the experiments were conducted. This paper considers average velocity and Reynolds stress and utilizes the proper orthogonal decomposition method to study flow characteristics. The results indicate that the rotation-induced Coriolis force, centrifugal force, and radial pressure gradient in the radial direction influence the jet to deflect. The pressure gradient generated by the centrifugal force weakens its effect, making the jet deflection primarily dominated by the Coriolis force. The deflection direction and degree of the jet differ with the rotation direction and increase with the rotation number. When the rotation direction is reversed, differences in the direction of the force acting on the fluid lead to variations in the secondary flow structures of the jet; the secondary flow structures within the impingement holes exhibit two-vortex or four-vortex structures under counterclockwise or clockwise rotation, respectively. At the highest rotation number, jet deflection intensifies mixing with the surrounding fluid, resulting in a reduction of about 30% in the velocity peak compared to the stationary state but an increase of approximately 0.6 times in turbulent kinetic energy.

Numerical analysis of heat transfer characteristics in ribbed two-passed channel with varied cross section

Li,

Luo,

Yang

et al. 2024

The mid-chord region of turbine blades typically employs internal cooling channels to enhance heat transfer. However, traditional internal cooling channels are mostly designed in the form of straight channels, and studies based on it may not address the needs of variable cross section channels. Therefore, this study investigates the effect of rib configurations in variable cross section channels on channel performance. First, the cross sectional area of the two-passed channels is modified by altering the inclination angle of the dividers (−3°, 0°, and +3°). The flow pattern and heat transfer features within a two-passed channel with variable cross section under four different rib configurations of NP, NN, PN, and PP are investigated using numerical simulation. N denotes the ribs rotated 45° clockwise relative to the flow direction, while P denotes the ribs rotated 45° counterclockwise. Subsequently, the optimal rib configuration within the variable cross sectional two-passed channels is determined for Reynolds numbers ranging from 10 000 to 50 000. Results show that, at +3°, the PP exhibits the maximum decrease of up to 18.2% in transfer performance factor (TPF), while at −3°, the NN shows the maximum decrease of up to 12.7%. It is evident that the optimal rib configuration for two-passed channels under different divider inclinations is not consistent. At +3°, the NP exhibits the best TPF, while at −3°, the PP demonstrates the optimal TPF. This study provides insights into selecting appropriate rib configurations when the cross sectional area of internal channels within turbine blades varies. Compared to the studies that have focused on traditional straight channels, the research provides guidance for the design of ribbed two-passed channels with varied cross section.