| 1. |
- Arroyo, Carlos, 1977, et al.
(författare)
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Experimental Heat Transfer Investigation of an Aggressive Intermediate Turbine Duct
- 2012
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Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 134:5
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Tidskriftsartikel (refereegranskat)abstract
- In most designs of two-spool turbofan engines, intermediate turbine ducts (ITDs) are used to connect the high-pressure turbine (HPT) with the low-pressure turbine (LPT). Demands for more efficient engines with reduced emissions require more "aggressive ducts," ducts which provide both a higher radial offset and a larger area ratio in the shortest possible length, while maintaining low pressure losses and avoiding nonuniformities in the outlet flow that might affect the performance of the downstream LPT. The work presented in this paper is part of a more comprehensive experimental and computational study of the flowfield and the heat transfer in an aggressive ITD. The main objectives of the study were to obtain an understanding of the mechanisms governing the heat transfer in ITDs and to obtain high quality experimental data for the improvement of the CFD-based design tools. This paper presents and discusses the results of the experimental study. The duct studied was a state-of-the-art "aggressive" design with nine thick nonturning structural struts. It was tested in a large-scale low-speed experimental facility with a single-stage HPT. In this paper measurements of the steady convective heat transfer coefficient (HTC) distribution on both endwalls and on the strut for the duct design inlet conditions are presented. The heat transfer measurement technique used is based on infrared thermography. Part of the results of the flow measurements is also included.
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| 2. |
- Aslanidou, Ioanna, et al.
(författare)
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Aerothermal Performance of Shielded Vane Design
- 2017
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 139:11
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental investigation of the concept of using the combustor transition duct wall to shield the nozzle guide vane leading edge. The new vane is tested in a high-speed experimental facility, demonstrating the improved aerodynamic and thermal performance of the shielded vane. The new design is shown to have a lower average total pressure loss than the original vane, and the heat transfer on the vane surface is overall reduced. The peak heat transfer on the vane leading edge–endwall junction is moved further upstream, to a region that can be effectively cooled as shown in previously published numerical studies. Experimental results under engine-representative inlet conditions showed that the better performance of the shielded vane is maintained under a variety of inlet conditions.
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| 3. |
- Aslanidou, Ioanna, et al.
(författare)
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Effect of the Combustor Wall on the Aerothermal Field of a Nozzle Guide Vane
- 2018
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 140:5
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Tidskriftsartikel (refereegranskat)abstract
- In gas turbines with can combustors the trailing edge of the combustor transition duct wall is found upstream of ev- ery second vane. This paper presents an experimental and numerical investigation of the effect of the combustor wall trailing edge on the aerothermal performance of the nozzle guide vane. In the measurements carried out in a high speed experimental facility, the wake of this wall is shown to in- crease the aerodynamic loss of the vane. On the other hand, the wall alters secondary flow structures and has a protective effect on the heat transfer in the leading edge-endwall junc- tion, a critical region for component life. The different clock- ing positions of the vane relative to the combustor wall are tested experimentally and are shown to alter the aerothermal field. The experimental methods and processing techniques adopted in this work are used to highlight the differences be- tween the different cases studied.
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| 4. |
- Aslanidou, Ioanna, et al.
(författare)
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Leading Edge Shielding Concept in Gas Turbines With Can Combustors
- 2012
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 135:2
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Tidskriftsartikel (refereegranskat)abstract
- The remarkable developments in gas turbine materials and cooling technologies haveallowed a steady increase in combustor outlet temperature and, hence, in gas turbine efficiencyover the last half century. However, the efficiency benefits of higher gas temperature,even at the current levels, are significantly offset by the increased losses associatedwith the required cooling. Additionally, the advancements in gas turbine cooling technologyhave introduced considerable complexities into turbine design and manufacture.Therefore, a reduction in coolant requirements for the current gas temperature levels isone possible way for gas turbine designers to achieve even higher efficiency levels. Theleading edges of the first turbine vane row are exposed to high heat loads. The high coolantrequirements and geometry constraints limit the possible arrangement of the multiplerows of film cooling holes in the so-called showerhead region. In the past, investigatorshave tested many different showerhead configurations by varying the number of rows, inclinationangle, and shape of the cooling holes. However, the current leading edge coolingstrategies using showerheads have not been shown to allow a further increase inturbine temperature without the excessive use of coolant air. Therefore, new coolingstrategies for the first vane have to be explored. In gas turbines with multiple combustorchambers around the annulus, the transition duct walls can be used to shield, i.e., to protect,the first vane leading edges from the high heat loads. In this way, the stagnationregion at the leading edge and the showerhead of film cooling holes can be completelyremoved, resulting in a significant reduction in the total amount of cooling air that is otherwiserequired. By eliminating the showerhead the shielding concept significantly simplifiesthe design and lowers the manufacturing costs. This paper numerically analyzes the potentialof the leading edge shielding concept for cooling air reduction. The vane shape wasmodified to allow for the implementation of the concept and nonrestrictive relative movementbetween the combustor and the vane. It has been demonstrated that the coolant flowthat was originally used for cooling the combustor wall trailing edge and a fraction of thecoolant air used for the vane showerhead cooling can be used to effectively cool both thesuction and the pressure surfaces of the vane.
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| 5. |
- Baagherzadeh Hushmandi, Narmin, 1978-, et al.
(författare)
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Effects of multiblocking and axial gap distance on performance of partial admission turbines : A numerical analysis
- 2011
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 133:3, s. 031028-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the effects of axial gap distance between the first stage stator and rotor blades and multiblocking on aerodynamics and performance of partial admission turbines are analyzed numerically. The selected test case is a two stage axial steam turbine with low reaction blades operating with compressed air. The multiblocking effect is studied by blocking the inlet annulus of the turbine in a single arc and in two opposing blocked arcs, each having the same admission degree. The effect of axial gap distance between the first stage stator and rotor blades is studied while varying the axial gap by 20% compared with the design gap distance. Finally, full admission turbine is modeled numerically for comparison. Performance of various computational cases showed that the first stage efficiency of the two stage partial admission turbine with double blockage was better than that of the single blockage turbine; however, the extra mixing losses of the double blockage turbine caused the efficiency to deteriorate in the downstream stage. It was shown that the two stage partial admission turbine with smaller axial gap than the design value had better efficiency of the first stage due to lower main flow and leakage flow interactions; however, the efficiency at the second stage decreased faster compared with the other cases. Numerical computations showed that the parameters, which increased the axial force of the first stage rotor wheel for the partial admission turbine, were longer blocked arc, single blocked arc, and reduced axial gap distance between the first stage stator and rotor blades.
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| 6. |
- Baagherzadeh Hushmandi, Narmin, et al.
(författare)
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Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines
- 2011
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 133:4, s. 041017-1-041017-12
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Tidskriftsartikel (refereegranskat)abstract
- A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage's stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage's stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.
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| 7. |
- Binder, Christian, et al.
(författare)
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Experimental Study on Pressure Losses in Circular Orifices for the Application in Internal Cooling Systems
- 2015
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Ingår i: Journal of turbomachinery. - : ASME Press. - 0889-504X .- 1528-8900. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- The cooling air flow in a gas turbine is governed by the flow through its internal passages and controlled by restrictors such as circular orifices. If the cooling air flow is incorrectly controlled, the durability and mechanical integrity of the whole turbine may be affected. Consequently, a good understanding of the orifices in the internal passages is important. This study presents experimental results for a range of pressure ratios and length-to-diameter ratios common in gas turbines including even very small pressure ratios. Additionally, the chamfer depth at the inlet was also varied. The results of the chamfer depth variation confirmed its beneficial influence on decreasing pressure losses. Moreover, important effects were noted when varying more than one parameter at a time. Besides earlier mentioned hysteresis at the threshold of choking, new phenomena were observed, e.g. a rise of the discharge coefficient for certain pressure and length-to-diameter ratios. A correlation for the discharge coefficient was attained based on the new experimental data with a generally lower error than previous studies.
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| 8. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Wake Analysis of an Aerodynamically Optimized Boxprop High Speed Propeller
- 2019
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Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 141:9
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Tidskriftsartikel (refereegranskat)abstract
- The Boxprop is a novel, double-bladed, tip-joined propeller for high-speed flight. The concept draws inspiration from the box wing concept and could potentially decrease tip vortex strength compared with conventional propeller blades. Early Boxprop designs experienced significant amounts of blade interference. By performing a wake analysis and quantifying the various losses of the flow, it could be seen that these Boxprop designs produced 45% more swirl than a conventional reference blade. The reason for this was the proximity of the Boxprop blade halves to each other, which prevented the Boxprop from achieving the required aerodynamic loading on the outer parts of the blade. This paper presents an aerodynamic optimization of a 6-bladed Boxprop aiming at maximizing efficiency and thrust at cruise. A geometric parametrization has been adopted which decreases interference by allowing the blade halves to be swept in opposite directions. Compared with an earlier equal-thrust Boxprop design, the optimized design features a 7% percentage point increase in propeller efficiency and a lower amount of swirl and entropy generation. A vortex-like structure has also appeared downstream of the optimized Boxprop, but with two key differences relative to conventional propellers. (1) Its formation differs from a traditional tip vortex and (2) it is 46% weaker than the tip vortex of an optimized 12-bladed conventional propeller.
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| 9. |
- Dahlqvist, Johan, et al.
(författare)
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Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds
- 2018
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Ingår i: Journal of turbomachinery. - : ASME Press. - 0889-504X .- 1528-8900. ; 140:3
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Tidskriftsartikel (refereegranskat)abstract
- The aspect of hub cavity purge has been investigated in a high-pressure axial lowreaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the cavities below the hub level from the hot main annulus flow. A fullscale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely, a high loading design case, and two high-speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. Observing the effect of the purge rate on measurement plane averaged parameters, a minor flow angle decrease and Mach number increase is seen for the low speed case, while maintaining near constant values for the higher operating speeds. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.
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| 10. |
- De Vincentiis, Luca, 1991-, et al.
(författare)
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Effects of Upstream Wakes on the Boundary Layer Over a Low-Pressure Turbine Blade
- 2023
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 145:5
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the evolution of the boundary layer over a low-pressure turbine blade is studied using direct numerical simulations, with the aim of investigating the unsteady flow field induced by the rotor-stator interaction. The freestream flow is characterized by the high level of freestream turbulence and periodically impinging wakes. As in the experiments, the wakes are shed by moving bars modeling the rotor blades and placed upstream of the turbine blades. To include the presence of the wake without employing an ad-hoc model, we simulate both the moving bars and the stationary blades in their respective frames of reference and the coupling of the two domains is done through appropriate boundary conditions. The presence of the wake mainly affects the development of the boundary layer on the suction side of the blade. In particular, the flow separation in the rear part of the blade is suppressed. Moreover, the presence of the wake introduces alternating regions in the streamwise direction of high- and low-velocity fluctuations inside the boundary layer. These fluctuations are responsible for significant variations of the shear stress. The analysis of the velocity fields allows the characterization of the streaky structures forced in the boundary layer by turbulence carried by upstream wakes. The breakdown events are observed once positive streamwise velocity fluctuations reach the end of the blade. Both the fluctuations induced by the migration of the wake in the blade passage and the presence of the streaks contribute to high values of the disturbance velocity inside the boundary layer with respect to a steady inflow case. The amplification of the boundary layer disturbances associated with different spanwise wavenumbers has been computed. It was found that the migration of the wake in the blade passage stands for the most part of the perturbations with zero spanwise wavenumber. The non-zero wavenumbers are found to be amplified in the rear part of the blade at the boundary between the low- and high-speed regions associated with the wakes.
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