Effects of Inlet Temperature Uniformity and Nonuniformity on the Tip Leakage Flow and Rotor Blade Tip and Casing Heat Transfer Characteristics

Abstract

High thermal load appears at the blade tip and casing of a gas turbine engine. It becomes a significant design challenge to protect the turbine materials from this severe situation. As a result of geometric complexity and experimental limitations, computational fluid dynamics tools have been used to predict blade tip leakage flow aerodynamics and heat transfer at typical engine operating conditions. In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (444 K) and high (800 K) inlet temperatures and nonuniform (parabolic) temperature profiles have been considered at a fixed rotor rotation speed (9500 rpm). The results showed that the change of flow properties at a higher inlet temperature yields significant variations in the leakage flow aerodynamics and heat transfer relative to the lower inlet temperature condition. Aerodynamic behavior of the tip leakage flow varies significantly with the distortion of turbine inlet temperature. For more realistic inlet condition, the velocity range is insignificant at all time instants. At a high inlet temperature, reverse secondary flow is strongly opposed by the tip leakage flow and the heat transfer fluctuations are reduced greatly.

Unsteady Analysis on the Effects of Tip Clearance Height on Hot Streak Migration Across Rotor Blade Tip Clearance

“…Yaras and Sjolander [43] conducted detailed experiments to explore the physical mechanism of the scraping flow (the reverse secondary flow [36]) by which the relative motion of the end wall affected the flow structure in tip gap and reduced the leakage flow rate. In Fig.…”

“…According to the work of Krishnababu et al [41], Yang et al [31] and Rahman et al [36], the standard k-w, and SST k-w turbu lence models are capable of showing better agreement with the experimental data than k-s and other turbulence models in the researches on tip clearance. In order to validate the accuracy of the turbulence model used in the present paper, both of these two k-w turbulence models are examined in a steady numerical predic tion first, and the results are compared with the available experi mental data to select a better one.…”

“…In brief, five numerical cases with different tip gap heights, blade profiles, and inlet boundary conditions are summar ized in Table 2. In radial and circumferential directions, the temperature profiles with hot streak are set as para bolic curves by referencing [24] and [36], in order to simulate the actual turbine inlet conditions. Inlet total pressure is set at 344,750 Pa, and the pressure ratio of 2.25 determines the static pressure of 153,222 Pa at the outlet.…”

“…For the simulation of the leakage flow and heat transfer near the blade tip region in a gas turbine, commercial CFD software CFX was recommended [31,36]. In the present study, 3D viscid steady and unsteady simulations are performed using the software package ANSYS CFX 11.0.…”

“…Unsteady experimental measure ments for blade tip heat transfer of a Rolls Royce aero-engine were carried out by Chana and Jones [34] in the QinetiQ ILPF. Rahman et al [36] conducted a numerical simulation with the SST k-w turbulence model to investigate the effects of different inlet temperature conditions on blade tip leakage flow and heat transfer. The radial extending of hot fluid amplified by tip gap increases the integral surface temperature of rotor blade [35].…”