Abstract:Tip clearance flow between rotating blades and the stationary casing in high-pressure turbines is very complex and is one of the most important factors influencing turbine performance. The rotor with a winglet-cavity tip is often used as an effective method to improve the loss resulting from the tip clearance flow. In this study, an aerodynamic geometric optimisation of a winglet-cavity tip was carried out in a linear unshrouded high-pressure axial turbine cascade. For the purpose of shaping the efficient wing… Show more
“…Zhou et al. 26 also shows that the standard k-ω turbulence model achieved better predictions on the tip aerodynamic performance. Figure 3.The cascade geometry for turbulence model validation.Figure 4.Comparison of heat transfer coefficient contour distribution among experimental data and four turbulence models: (a) standard k-ɛ model; (b) standard k-ω model; (c) RNG k-ɛ model; (d) SST k-ω model.SST: shear stress transport.…”
The steady simulation with flow field and heat transfer performance for different rib layouts is investigated. By referring the GE-E3 turbine blade tip (Case 1) profile as a prototype model, four kinds of rib layouts of full rib structure (Case 2), half rib structure connected with suction side (Case 3), half rib structure connected with pressure side (Case 4), and half rib structure in the rear squealer cavity (Case 5) was designed. The availability of k-ω turbulence model was validated through comparison of heat transfer coefficient distribution with the experimental data. The area-averaged heat transfer coefficients of Case 5 decreases up to 11.3%, 3.1%, 11.3%, and 2.8% in comparison to Cases 1, 2, 3, and 4. The total pressure coefficient of Case 5 reduces by 1.4%, 2.7%, and 4.0% compared to Cases 1, 2, and 3. The results reveal that, among the five novel rib layout cases, Case 5 obtains the optimal comprehensive performance under the performance of considering tip heat transfer and cascade loss. Further investigation on the influence of Cases 1 and 5 at different rotational speeds on the flow field and heat transfer characteristics of the tip clearance is also illustrated and discussed.
“…Zhou et al. 26 also shows that the standard k-ω turbulence model achieved better predictions on the tip aerodynamic performance. Figure 3.The cascade geometry for turbulence model validation.Figure 4.Comparison of heat transfer coefficient contour distribution among experimental data and four turbulence models: (a) standard k-ɛ model; (b) standard k-ω model; (c) RNG k-ɛ model; (d) SST k-ω model.SST: shear stress transport.…”
The steady simulation with flow field and heat transfer performance for different rib layouts is investigated. By referring the GE-E3 turbine blade tip (Case 1) profile as a prototype model, four kinds of rib layouts of full rib structure (Case 2), half rib structure connected with suction side (Case 3), half rib structure connected with pressure side (Case 4), and half rib structure in the rear squealer cavity (Case 5) was designed. The availability of k-ω turbulence model was validated through comparison of heat transfer coefficient distribution with the experimental data. The area-averaged heat transfer coefficients of Case 5 decreases up to 11.3%, 3.1%, 11.3%, and 2.8% in comparison to Cases 1, 2, 3, and 4. The total pressure coefficient of Case 5 reduces by 1.4%, 2.7%, and 4.0% compared to Cases 1, 2, and 3. The results reveal that, among the five novel rib layout cases, Case 5 obtains the optimal comprehensive performance under the performance of considering tip heat transfer and cascade loss. Further investigation on the influence of Cases 1 and 5 at different rotational speeds on the flow field and heat transfer characteristics of the tip clearance is also illustrated and discussed.
“…A method of geometric parameterization about the winglet-cavity tip has been detailed described in the previous study. 36 For performance matching between upstream row and downstream row in real turbines, the geometry of the leading edge and trailing edge are unchanged in the optimization process. Based on an initial flat tip, the shape of the winglet is first generated by the variable offset in the normal direction of the profile between the beginning and ending position.…”
Section: Experimental Apparatus and Methodsmentioning
confidence: 99%
“…The winglet-cavity tip was found to have a lower tip leakage mass flow rate than the flat tip and thus has smaller tip leakage losses in the previous work. 36 The distribution of pitchwise-averaged aerodynamic parameters of these three types of tips are compared in Figure 6 at a tip clearance of / H ¼ 1.0%. Figure 6(a) illustrates the distribution of the yaw angle at the outlet.…”
Section: Flow Loss and Secondary Flow At Exitmentioning
confidence: 99%
“…32 The influence of boundary conditions can be found in Coull et al 33 The effects of compressibility can be found in O'Dowd et al 34 and Wheeler et al 35 In this paper, the effects of the winglet-cavity tip on the aerodynamic performance of the turbine cascade have been investigated in a low-speed wind tunnel. A detailed description of the optimized winglet-cavity tip is shown in Zhou et al 36 The aerodynamic parameters and the flow field of the flat tip, cavity tip, and winglet-cavity tip are compared and analyzed with a tip clearance of /H ¼ 1.0%. Based on the detailed endwall oil-flow visualizations and static pressure, the flow field and tip leakage flow are analyzed.…”
The effects of a novel winglet-cavity tip on the flow field and aerodynamic performance of a turbine blade with tip clearance have been investigated in a low-speed wind tunnel. A calibrated five-hole probe is used for the measurement of three-dimensional flows downstream of the cascade. The method of oil-flow visualization is used to show the endwall flow field structure. The distribution of endwall static pressure is measured particularly by using the special moveable endwall. The downstream results show that, compared with the flat tip and cavity tip, the winglet-cavity tip reduces aerodynamic loss in the region of tip leakage vortex and passage vortex effectively and gives a 8.5% reduction of total pressure losses at a tip clearance of τ/ H = 1.0%. Meanwhile, a more uniform flow angle is obtained with the winglet-cavity tip. Thus, the winglet-cavity tip provides better aerodynamic performance. It was found that more endwall flow enters the cavity from the front of suction side gap, combines with the flow entering the tip from the pressure side, and then separates upon the cavity. This reduces the loss of passage vortex. The endwall static pressure indicates that the winglet-cavity tip reduces the driving pressure difference and weakens the tip leakage flow. With the tip clearance increasing, the leakage flow is significantly enhanced. This strengthens the interaction between the tip leakage vortex and the passage vortex. With respect to the flat tip and cavity tip, the winglet-cavity tip obtains the lowest total pressure loss at all tested tip clearances.
“…6,7 Some combined control technologies at the clearance region have been put forward recently, e.g. casing treatment and blowing, 8 winglet and squealer, 9,10 and honeycomb seal. 11,12 However, the relative motion between the blade and shroud endwall has been neglected in these studies.…”
The tip clearance flow could lead to work reduction and loss generation in turbomachines. However, the effect of separation at low Reynolds number on leakage flow is seldom studied. The previous method for evaluating tip leakage characteristics should also be further researched. Thus, numerical investigations on the tip clearance flow in an unshrouded axial-inflow turbine are conducted at low Reynolds number (3.5 × 104 of the rotor outlet at the designed condition) in the present study. The flow patterns and leakage mass flow rate of the clearance have been analyzed in detail. It is found that the tip clearance flow is greatly affected by the flow separation caused by low Reynolds number. The scraping ratio adopted in previous references does not accord with the clearance flow characteristics at low Reynolds number, especially in the front part of the clearance. A coefficient by −0.70 power of the Reynolds number is proposed to modify the scraping ratio in the present study. The synergy between the velocity and the pressure gradient is innovatively employed to research the tip clearance flow characteristics, and it gives a reliable criterion of indicating the flow patterns in the tip clearance.
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