旋转带肋通道流阻特性研究

With the development of aero-engines, the turbine inlet temperature continues to rise. In order to ensure the safety and reliability of the turbine blades, cooling structures must be set inside turbine blades to cool them. Heat transfer coefficient and flow resistance are the key parameters to measure the cooling characteristics of internal cooling structures. In this paper, the characteristics of flow resistance in a rotating ribbed channel is presented numerical simulation under different rib spacings, rib angles, and thermal boundary conditions. The results show that, separation and reattachment of fluid between ribs is the key effect of rib spacing on flow resistance. The flow resistance is small when the rib spacing is small, because it's difficult for the fluid to form reattachment between the ribs. With the increase of rib spacing, the reattachment phenomenon is more obvious and the flow resistance increases accordingly. In general,p: e=10 channel has the maximum flow resistance. Secondary flow caused by the ribs is the key factor affecting the flow resistance characteristics with different rib angles. The secondary flow interacts with the main flow and causes flow loss through mixing, thus affecting the flow resistance of the channel. Under static condition, the flow resistance of 60°ribbed channel is the largest. The flow resistance of channel was affected by the temperature rise ratio also. And with the increase of the Ro, the temperature rise ratio has a more obvious effect on the flow resistance of the ribbed channel.When Ro=0.45, the flow resistance of the channel with a temperature rise ratio of 0.4 is 2.4 times that of the channel without temperature rise, while when Ro=0.3, it is 1.6 times, and when Ro=0.15, it is 1.2 times.

Analysis of Film Cooling Effectiveness on Shaped Hole and Antivortex Hole

Film cooling is introduction of a secondary fluid （coolant or injected fluid） at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.

Impacts of Startup,Shutdown and Load Variation on Transient Temperature and Thermal Stress Fields within Blades of Gas Turbines

Based on the actual operation parameters and temperature-dependent material properties of a gas turbine unit,composite cooling blade model and corresponding reliable boundary conditions were established.Transient thermal-fluid-solid coupling simulations were then comprehensively conducted to analyze the transient flow and the temperature field of the blade under startup,shutdown,and variable loads condition.Combined with the obtained transient temperature data,the non-linear finite element method was exploited to examine the effect of these transient operations on the turbine blade thermal stress characteristics.Results show that the temperature and pressure on the blade surface increase with the load level and vice versa.As the startup process progresses,the film cooling effectiveness and the heat convection of airflows inside the blade continuously grow;high-temperature areas on the pressure surface and along the trailing edge of the blade tip gradually disappear.Locally high-temperature zones with the maximum of 1280 K are generated at the air inlet and outlet of the blade platform and the leading edge of the blade tip.The high thermal stresses detected on the higher temperature side of the temperature gradient are commonly generated in places with large temperature gradients and significant geometry variations.For the startup/shutdown process,the rate of increase/decrease of the thermal stress is positively correlated with the load variation rate.A slight variation rate of the load(1.52%/min)can lead to an apparent alteration(41%)to the thermal stress.In operations under action of the variable load,although thermal stress is less sensitive to the load variation,the rising or falling rate of the exerted load still needs to be carefully controlled due to the highly leveled thermal stresses.

Simulation of the secondary air system of turbofan engines:Insights from 1D-3D modeling

Focusing on the internal flow and heat transfer analysis,a platform for the performance evaluation of the Secondary Air System(SAS)is developed.A multi-fidelity modeling technique has been developed in a turbofan engine model under different flight conditions.A turbine blade cool-ing model which integrates external heat transfer calculations and coolant side modeling with com-mon components is proposed.In addition,the Computational Fluid Dynamics(CFD)method is selected to capture the complex flow field structure in the preswirl system.The validity of the SAS models is compared with publicly available data.An elaborately designed cooling system for the AGTF30 engine is analyzed through three main branches.It is found that the 1D-3D mod-eling technique can provide more accurate predictions of the SAS for the AGTF30 engine.The results demonstrate the versatility and flexibility of the SAS models,thereby indicating the capacity of meeting most of the demands of flow and thermal analysis of the SAS.

Heat transfer characteristics in a rotating AR=4:1 channel with different channel orientations at high rotation numbers

In order to reveal the effect of channel orientations on rotational heat transfer performance,this paper presents an experimental model of AR=4:1 smooth rectangular channel.The stationary and rotational heat transfer characteristics of the channel are studied in the range of Re=10,000-40,000 and Ro=0-1.23 under the channel orientation of 90°and 135°,which represent the basic one and realistic one,respectively.The experimental results indicate that for the trailing wall,the 90°channel shows a typical large range enhancement of rotational heat transfer,while the rotational effect becomes negative in most areas at 135°case.As the rotation number exceeds 0.7,the heat transfer of the trailing surface is greatly improved by rotational effect in 90°channel.When the channel was orientated at 135°,the leading surface heat transfer is more sensitive to rotation under the low rotation number(Ro<0.3),and 20%-30%worse than non-rotating cases.The averaged Nusselt ratios correlations under the channel orientation of 90°and 135°have been developed for further engineering applications.