Inlet Hot Streak Research Articles

Numerical analysis on effects of inlet pressure and temperature non-uniformities on aero-thermal performance of a HP turbine

Unsteady numerical studies were conducted on the effects of combustor exit total pressure non-uniformity and hot streak (HS) on the aero-thermal characteristics of a high-pressure (HP) turbine stage. Firstly, four total pressure profiles including uniform, turbulent boundary layer, realistic engine combustor exit and radial reverse total pressure (higher total pressure near the endwall) were applied to reveal the vortex structures and heat transfer characteristics of the turbine. Then the four total pressure profiles coupled with inlet HS were specified to study the HS migration mechanisms. The results indicated that the turbulent boundary layer total pressure intensifies the passage vortices (PVs) while the higher total pressure near the endwall induces counter rotating vortices (CRVs), in both the stator and rotor passages. The heat transfer on the vane and blade surfaces was affected by the vortices and the extent of the impact directly depends on the intensity of the vortices, which is determined by the gradient of the total pressure. The heat transfer coefficients (HTCs) on the vane and blade pressure surface are increased by 104% and 20–30%, respectively, due to the CRV effects. The increase of tip leakage flow for the higher total pressure near the tip enhances the tip pressure side HTC by 4% comparing with the uniform case. The PVs and CRVs from the stator passage persistently exist in the rotor passage near the suction side endwall while have negligible influence on the rotor heat transfer. The migration paths of the hot streak are significantly affected by the PVs and CRVs in the stator passage, and the rotor blade surface temperature is dominated by both of the redistribution of HS in the vane passage and the vortices in the rotor passage. The PVs extend the HS radial migration and increase the vane and blade surface temperature. While the CRVs circulate the hot fluid away from the vane surface and increase the HS attenuation, thus decrease the vane and blade surface temperature significantly. The total pressure non-uniformity also decreases the turbine adiabatic efficiency by 0.6% at uniform inlet temperature condition.

Influence of Mainstream Turbulence Intensity on Heat Transfer Characteristics of a High Pressure Turbine Stage With Inlet Hot Streak

An unsteady computational study was carried out on GE-E3 high pressure (HP) turbine at inflow turbulence intensities of 5%, 10%, and 20% accompanying with inlet hot streak (HS) at two circumferential positions (impinging and nonimpinging relative to vane leading edge) to analyze the interacted turbulence and HS influences. Turbulence decay mechanisms in turbine passage were presented, and the airfoil heat transfer behaviors were explored by means of adiabatic wall temperature, heat transfer coefficient (HTC), and wall heat flux. The results indicate that the elevated turbulence leads to favorable turbine airfoil temperature distributions, and turbulence induced HS attenuation mainly occurs in vane passage. In addition, the HS dispersion is related directly to the temperature gradients. Although the endwall temperature increases by more than 20 K (2.8% inlet mass-averaged temperature) and midregion temperature decreases by 16 K at blade leading edge, the hot region on blade pressure surface (PS) is only weakened by about 7 K, when turbulence intensity is increased from 5% to 20%. Higher turbulence significantly affects the airfoil HTC, excepting the regions secondary and leakage flow effects are dominating. Therefore, the tip and blade suction surface (SS) trailing edge heat flux is decreased for the temperature decline at higher turbulence, which is beneficial to tip cooling. HS position not only affects the airfoil surface temperature variations but also slightly affects the vane and blade midspan HTC for the variation of heat transfer driving temperature.

Rotor Blade Heat Transfer of High Pressure Turbine Stage Under Inlet Hot-Streak and Swirl

A key consideration in high pressure (HP) turbine designs is the heat load experienced by rotor blades. Impact of turbine inlet nonuniformity of combined temperature and velocity traverses, typical for a lean-burn combustor exit, has rarely been studied. For general turbine aerothermal designs, it is also of interest to understand how the behavior of lean-burn combustor traverses (with both hot-streak and swirl) might contrast with those for a rich-burn combustor (largely hot-streak only). In the present work, a computational study has been carried out on the aerothermal performance of a HP turbine stage under nonuniform temperature and velocity inlet profiles. The analyses are primarily conducted for two combined hot-streak and swirl inlets, with opposite swirl directions. In addition, comparisons are made against a hot-streak only case and a uniform inlet. The effects of three nozzle guide vane (NGV) shape configurations are investigated: straight, compound lean (CL) and reverse CL (RCL). The present results reveal a qualitative change in the roles played by heat transfer coefficient (HTC) and fluid driving (“adiabatic wall”) temperature, Taw. It has been shown that the blade heat load for a uniform inlet is dominated by HTC, whilst a hot-streak only case is largely influenced by Taw. However, in contrast to the hot-streak only case, a combined hot-streak and swirl case shows a role reversal with the HTC being a dominant factor. Additionally, it is seen that the swirling flow redistributes radially the hot fluid within the NGV passage considerably, leading to a much ‘flatter’ rotor inlet temperature profile compared to its hot-streak only counterpart. Furthermore, the rotor heat transfer characteristics for the combined traverses are shown to be strongly dependent on the NGV shaping and the inlet swirl direction, indicating a potential for further design space exploration. The present findings underline the need to clearly define relevant combustor exit temperature and velocity profiles when designing and optimizing NGVs for HP turbine aerothermal performance.

Hot Streak and Vane Coolant Migration in a Downstream Rotor

This paper describes a method of improving the cooling of the hub region of high-pressure turbine (HPT) rotor by making better use of the unsteady coolant flows originating from the upstream vane. The study was performed computationally on an engine HPT stage with representative inlet hot streak and vane coolant conditions. An experimental validation study of hot streak migration was undertaken on two low-speed test facilities. The unsteady mechanisms that transport hot and cold fluid within the rotor hub region are first examined. It was found that vortex-blade interaction dominated the unsteady transport of hot and cold fluid in the rotor hub region. This resulted in the transport of hot fluid onto the rotor hub and pressure surface, causing a peak in the surface gas temperatures. The vane film coolant was found to have only a limited effect in cooling this region. A new cooling configuration was thus examined which exploits the unsteadiness in rotor hub to aid transport of coolant towards regions of high rotor surface temperatures. The new coolant was introduced from a slot upstream of the vane. This resulted in the feed of slot coolant at a different phase and location relative to the vane film coolant within the rotor. The slot coolant was entrained into the unsteady rotor secondary flows and transported towards the rotor hub-pressure surface region. The slot coolant reduced the peak time-averaged rotor temperatures by a similar amount as the vane film coolant despite having only a sixth of the coolant mass flow.

Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine

In this paper, three-dimensional multiblade row unsteady Navier–Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in high pressure stage of a vaneless counter-rotating turbine. The numerical results indicate that the migration characteristics of the hot streak in the high pressure turbine rotor are dominated by the combined effects of secondary flow, buoyancy, and leakage flow in the rotor tip clearance. The leakage flow trends to drive the hotter fluid toward the blade tip on the pressure surface and to the hub on the suction surface. Under the effect of the leakage flow, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the high pressure turbine rotor is intensified due to the effects of the leakage flow. And the results indicate that the leakage flow effects trend to increase the low pressure turbine rotor inlet temperature at the tip region. The air flow with higher temperature at the tip region of the low pressure turbine rotor inlet will affect the flow and heat transfer characteristics in the downstream low pressure turbine.

Analysis of Hot Streak Effects on Turbine Rotor Heat Load

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multiblade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed on elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10–30 percent (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified that drive the heat load nonuniformity: buoyancy, wake convection (the Kerrebrock–Mikolajczak effect), and Rotor–Stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space, which minimizes the adverse effects of hot streaks.