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Thermodynamic and aerodynamic measurements were carried out in a linear turbine cascade with transonic flow field. Heat transfer and adiabatic film-cooling effectiveness resulting from the interaction of the flow field and the ejected coolant at the endwall were measured and will be discussed in two parts. The investigations were performed in the W...
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... endwall used for measuring heat transfer and adiabatic filmcooling effectiveness consists of a high-temperature plastic material (TECATRON) with a thermal conductivity of 0.2W/mK and a maximum operating temperature of about 500K (Fig. 3). In order to create a constant specific heat flux, heating foils were appended on the wetted surface of the passage. The heating foils were composed of manganin-meander. This material´s resistance changes at only 10 -5 /K caused by temperature. Conduction losses at the endwall ...
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Citations
... Mclean et al. [4,5] and Kost et al. [6] conducted early studies on the influence of wheel space coolant injection in turbines, especially on the endwall region. They pointed out that due to the interaction of cooled air and the mainstream, this leakage flow intensifies the intricacy of the three-dimensional flow characteristics on the endwall surface, and even a Energies 2023, 16,7976 2 of 19 small amount of coolant injection (1%) has a significant impact on the aerodynamic and flow field structures of the stage. ...
During the practical operation of gas turbines, relatively cooled air from the compressor and the rim seal is applied in order to prevent mainstream ingestion into the space between the rotor and stator disc cavities, which can prolong the service life of hot components. On the one hand, the purge flow from the rim seal will inevitably interact with the mainstream and result in secondary flow on the endwall. On the other hand, it can also provide an additional cooling effect. In this paper, four rim seal structures, including an original single-tooth seal (ORI), a double-tooth seal (DS), a single-tooth seal with an adverse direction of the coolant purge flow and mainstream (AS) and a double-tooth seal with an adverse direction of the coolant purge flow and mainstream (ASDS), are experimentally and numerically investigated with mass flow ratios of 0.5%, 1.0% and 1.5%. The flow orientation of the coolant from the rim seal is considered as one of the main factors. The pressure-sensitive paint technique is used to experimentally measure the film cooling effectiveness on the endwall, and flow field analysis is conducted via numerical simulations. The results show that the cooling effect decreases in the cases of DS and ASDS. AS and ASDS can achieve a better film cooling performance, especially under a higher mass flow ratio. Furthermore, the structural changes in the rim seal have little impact on the aerodynamic performance. AS and ASDS can both achieve a better aerodynamic and film cooling performance.
... Hence, measuring the heat transfer characteristics and pressure field on the surface of turbine endwalls holds great significance in comprehending the distribution of thermal load and facilitating the design of turbine endwall cooling. In studying endwall film cooling, researchers employed various experimental methods, such as infrared camera systems [104,105], pressure-sensitive paint (PSP) [29,37,75,76,80,81,83,[106][107][108][109], temperature-sensitive paint (TSP) [26,75,106,110] and the steady-state liquid crystal technique [111]. ...
... Nicklas [104] conducted a comparative investigation on the effects of coolant ejection from a slot and three rows of holes. Endwall temperatures in the transonic flow field were measured using an infrared camera system in a rectilinear wind tunnel. ...
With an increased inlet gas temperature and the homogenization of the combustion chamber outlet temperature, the endwalls of gas turbines are exposed to extremely high heat loads. The complex flow structure of turbine endwalls makes it difficult to cool some regions of the endwalls, which can easily cause endwall ablation, reducing turbine aerodynamic performance and threatening the turbine’s safe operation. In order to improve the cooling and aerodynamic performance of gas turbines, the flow structure, heat transfer and film cooling characteristics of endwalls are analyzed in depth in this paper. This paper summarizes and analyzes the development of the aerodynamic heat transfer and film cooling of gas turbine endwalls in terms of geometric structures and flow boundary conditions and also presents new research directions. Based on the literature, the development and challenge of turbine endwall film cooling are also discussed.
... The arrangement of endwall film cooling holes is based on varied principles, resulting in six different configurations, as shown in Figure 2. Pattern A and Pattern B have their roots in previous arrangements derived from references [20,32]. Pattern B, in particular, considers the effects of the slot that forms when two endwall components are assembled. ...
To protect turbine endwall from heat damage of hot exhaust gas, film cooling is the most significant method. The complex vortex structures on the endwall, such as the development of horseshoe vortices and transverse flow, affects cooling coverage on the endwall. In this study, the effects of gas thermophysical properties on full-range endwall film cooling of a turbine vane are investigated. Three kinds of gas thermophysical properties models are considered, i.e., the constant property gas model, ideal gas model, and real gas model, with six full-range endwall film cooling holes patterns based on different distribution principles. From the results, when gas thermophysical properties are considered, the coolant coverage in the pressure side (PS)-vane junction region is improved in Pattern B, Pattern D, Pattern E, and Pattern F, which are respectively designed based on the passage middle gap, limiting streamlines, heat transfer coefficients (HTCs), and four-holes pattern. Endwall η distribution is mainly determined by relative ratio of ejecting velocity and density of the hot gas and the coolant. For the cooling holes on the endwall with an injection angle of 30°, the density ratio is more dominant in determining the coolant coverage. At the injection angle of 45°, i.e., the slot region, the ejecting velocity is more dominant in determining the coolant coverage. When the ejecting velocity Is large enough from the slot, the coolant coverage on the downstream endwall region is also improved.
... This process was visualized clearly by Friedrichs et al. [7], who claimed that the cooled and uncooled region due to vortex interaction should be considered in the design phase. Kost and Nicklas [8] studied the strong interactions between horseshoe and passage vortex along with the coolant jet. Their results show that the endwall film cooling effectiveness decreased significantly near PS because of the existence of a passage vortex. ...
As continuous of the previous sand-dune-inspired design, the Barchan-Dune-Shaped Injection Compound (BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically. While the public 777-shaped hole was served as a baseline, the BDSIC’s endwall effectiveness was assessed at various blowing ratios. Experiments were performed in a single-passage transonic wind tunnel using pressure-sensitive paint (PSP) technique. Carbon dioxide was used as coolant with density ratio of DR=1.53. The purge slot’s blowing ratio was fixed at M=0.3, but the coolant holes were adjusted within M=0.5−2.0. The measured experimental results indicate that the film distribution at the endwall is strongly affected by the passage flow structures. The BDSIC holes demonstrate much higher film effectiveness than the 777-shaped holes for all blowing ratios, ∼30% enhancement for regionally averaged effectiveness at M=1.0 and ∼26% at M=2.0. As shown by the numerical results, the existence of BDSIC reduced the coolant penetration effect at a higher blowing ratio. Coolant was deflected and its momentum increased in the streamwise direction, therefore providing more robust film coverage over the endwall region. The anti-counter-rotating vortex pair induced by the BDSIC further stabilized the coolant film and increased the coolant spreading downstream.
... It is necessary to know how secondary flows develop in transonic conditions, and how cooling along the endwall is affected. Limited studies have attempted to investigate endwall cooling with a high-speed mainstream flow [30][31][32][33]. These studies found a very complicated interaction of the mainstream and coolant flows. ...
The effects of mainstream flow velocity, density ratio (DR), and coolant-to-mainstream mass flow ratio (MFR) were investigated on a vane endwall in a transonic, annular cascade. A blow down facility consisting of five vanes was used. The film cooling effectiveness was measured using binary pressure sensitive paint (BPSP). The mainstream flow was set using isentropic exit Mach numbers of 0.7 and 0.9. The coolant-to-mainstream density ratio varied from 1.0 to 2.0. The coolant to mainstream MFR varied from 0.75% to 1.25%. The endwall was cooled by eighteen discrete holes located upstream of the vane passage to provide cooling to the upstream half of the endwall. Due to the curvature of the vane endwall, the upstream holes provided uniform coverage entering the endwall passage. The coverage was effective leading to the throat of the passage, where the downstream holes could provide additional protection. Increasing the coolant flowrate increased the effectiveness provided by the film cooling holes. Increasing the density of the coolant increases the effectiveness on the endwall while enhancing the lateral spread of the coolant. Finally, increasing the velocity of the mainstream while holding the MFR constant also yields increased protection on the endwall. Over the range of flow conditions considered in this study, the binary pressure sensitive paint proved to be a valuable tool for obtaining detailed pressure and film effectiveness distributions.
... Barigozzi et al. [7] also noted the strengthening of the passage vortex with increasing purge flow rate. Combined heat transfer coefficient and film cooling effectiveness studies where presented by Nicklas [8] and Mathison et al. [9 and 10]. Nicklas [8] reported the intensification of the horse-shoe vortex and relevant heat transfer coefficients with increasing slot coolant. ...
... Combined heat transfer coefficient and film cooling effectiveness studies where presented by Nicklas [8] and Mathison et al. [9 and 10]. Nicklas [8] reported the intensification of the horse-shoe vortex and relevant heat transfer coefficients with increasing slot coolant. The horse-shoe vortex was also found to have a negative impact on film cooling effectiveness. ...
The turbine center frame (TCF) is an inherent component of turbofan aircraft engines and is used for connecting the high-pressure turbine (HPT) to the low-pressure turbine (LPT). Its position immediately downstream of the HPT makes it susceptible to the extremely high temperatures of future engines. Despite this, fundamental knowledge of heat transfer in TCFs and the influencing factors is still missing.
This paper presents a new 45° sector-cascade test rig specifically designed for fundamental studies of film cooling effectiveness and heat transfer coefficient in TCFs and for the development and validation of a measurement technique involving infrared thermography and heating foils.
Measurements of heat transfer coefficient in the TCF were taken for two purge-to-mainstream mass flow ratios corresponding to the case of no purge and nominal (to engine operation) purge. The magnitude of the heat transfer coefficients on the hub and strut surfaces was highly influenced by the various flow structures in the passage and by the velocity variation of the mainstream flow due to the “aggressive” design of the TCF. Heat transfer on the surface of the strut was mainly governed by boundary layer behavior (laminar near the leading edge and turbulent for the rest of the strut) augmented by the effect of the secondary flow structures.
Measurements of film cooling effectiveness were also taken for the single case of nominal purge. A region of high film cooling effectiveness was observed, extending from the purge cavity exit to about 40% of the passage axial length. In this region, the effectiveness decreased with increasing axial length. On the surface of the struts and fillet radii the film cooling effectiveness was found to be zero. This was attributed to the effect of the horse-shoe vortex which sweeps the purge flow away from the strut surface and dilutes it by continuously entraining hot mainstream flow.
... The results showed that the iso-pressure line arranged film cooling configuration has more uniform distribution of film cooling effectiveness while the axial arranged configuration has larger film cooling effectiveness values. F.Satta and G. Tanda [33] also compared film cooling effectiveness between two discrete hole configuations on a flat endwall, and they found that by redesigning the hole configuration based on knowledge of the heat tranfer coefficient map on the endwall, a significant increase of the area-averaged film cooling effectiveness was achieved.Fredrich and Martin [34,35] measured thermodynamic and aerodynamic performance of a passage with upstream slot leakage and film cooling hole at the fore part of the passage on a flat endwall, the result show that film cooling effectiveness can be increase by the holes at the rear part of the passage. D.G Knost and K.A. Thole [36,37] also measured the film cooling performance with the combination of slot leakage and endwall discrete film cooling holes. ...
Full coverage film cooling arrangement is widely needed in nozzle guide vanes (NGVs) to keep the turbine surfaces from melting due to the unprecedented high turbine inlet temperature. Meanwhile, to reduce the passage aerodynamic losses, non-axisymmetric endwall contouring are widely applied. The employment of endwall contouring will impact the full coverage film cooling performance, thus changing the turbine durability. Thus, it is important to deeper know the effect of non-axisymmetric endwall contouring on endwall full coverage film cooling performance. In this study, Pressure Sensitivity Paint (PSP) technique is used to measure the full coverage film cooling effectiveness (η) distributions on a non-axisymmetric contoured endwall (CE) and the corresponding baseline endwall (BE) with several coolant mass flow ratios (MFRs). Meanwhile, cases with the corresponding experimental conditions by computational fluid dynamics (CFD) are done to calculate the blowing ratio (BR) and MFR distributions of the film cooling holes. The η distributions on the CE and the BE are compared, and the effect of MFR on the CE full coverage film cooling performance are documented. In addition, different turbulence models are evaluated on the ability to model the endwall film cooling problems by comparing the CFD results with the experimental results. With small MFR values, the film cooling performance are worse on the CE in the near-hole regions at the fore part of the passage but better on the CE in the far-hole regions and at the aft part of the passage than that on the BE. While with large MFRvalues, the CE perform better than the BE throughout the endwall surface.
... The interaction between the horseshoe and passage vortices with the coolant was investigated by Kost and Nicklas [4] and Nicklas [5]. They found that the film cooling effectiveness Fig. 1 Leakage flow through the purge slot decreases strongly toward the pressure side due to the passage vortex. ...
This study is concerned with the film cooling effectiveness of the flow issuing from the gap between the NGV and the transition duct on the NGV endwall, i.e. the purge slot. Different slot widths, positions and injection angles were examined in order to represent changes due to thermal expansion as well as design modifications. Apart from these geometric variations, different blowing ratios and density ratios were realized to investigate the effects of the interaction between secondary flow and film cooling effectiveness. The experimental tests were performed in a linear scale-1 cascade equipped with four highly loaded turbine vanes. The mainstream flow parameters were, with a Reynolds number of 300,000 and a Mach number (outlet) of 0.6, set to meet real engine conditions. The adiabatic film cooling effectiveness was determined by using the Pressure Sensitive Paint technique. In this context, nitrogen and carbon dioxide were used as tracer gases realizing two different density ratios DR = 1.0 and 1.6. The investigation was conducted for a broad range of blowing ratios with 0.25 < BR < 1.50. In combination with 10 geometry variations and the aforementioned blowing and density ratio variations 100 single operating points were investigated. For a better understanding of the coolant distribution, the secondary flows on the endwall were visualized by oil dye. The results provide a better insight into various parametric effects of gap variations on turbine vane endwall film cooling performance -- notably under realistic engine conditions.
... Kost and Nicklas [22] described the outcomes of strong coolant-mainstream interaction inside the blade passage and stated that detrimental effects of coolant ejection increases flow turbulence which was later confirmed by Liu and Yang [23]. Nicklas [24] identified an increase in Mach number at downstream trailing edge region where cooling becomes extremely difficult and suggested additional trailing edge cooling methods to provide better platform protection. Angular orientation of film holes towards pressure surface significantly reduces cross flow and provides better protection along pressure side-endwall corner [25]. ...
Secondary air bled from the compressor which bypasses the combustion chamber is used to seal the turbine components from incoming hot gas. Interaction of this secondary air (also known as purge flow) with the mainstream flow can alter the flow characteristics of turbine blade passage. This paper presents numerical investigation of interaction between ejected purge flow and mainstream flow in the presence of upstream disturbances/wakes. Steady as well as unsteady simulations are carried out using Reynolds Averaged Navier Stokes equations and SST turbulence model. The numerical results are validated with experimental measurements obtained at the blade exit region using an L shaped 5 hole probe and Scanivalve. Upstream wakes are generated by a circular cylinder, kept upstream of blade leading edge at different pitch-wise positions. For transient analysis cylinders are kept at stagnation line (STW) and middle of the blade passage (MW). The analysis reveals the interaction effects of two more additional vortices, viz. the cylinder vortex (Vc) and the purge vortex (Vp). Steady state analysis shows an increase in the underturning at blade exit due to the squeezing of the pressure side leg (PSL) of horse shoe vortex towards the pressure surface by the cylinder vortices (Vp). The unsteady analysis reveals the formation of filament shaped wake structures which breaks into smaller vortical structures at the blade leading edge for STW configuration. These filaments lead to the formation of additional pressure surface vortices. On the contrary, in MW configuration, the obstruction created by the purge flow causes the upper portion of cylinder vortices bend forward, creating a shearing action along the spanwise direction. In MW configuration, the horse shoe vortices generated from the upstream cylinder are broken by the purge vortex whereas in the STW configuration it slides over the purge vortex and move towards the suction surface under the influence of the pitchwise pressure gradient.
... According to the literature, there are mainly two different definitions of adiabatic cooling effectiveness in high-speed cascades. One is defined as [28]: ...
Endwall 2D contouring is a presently-employed design method for reducing the strength of secondary flows within gas turbine airfoil passages. Such contouring can lead to significant changes of passage flow. Also affecting passage flow is flow through an interface, or leakage slot, between the combustor and the turbine. Though introduced for eliminating ingression of passage gas into the cavity, leakage flow through the leakage slot, which has bypassed the combustor, can be used to cool the endwall and vane surfaces. Moreover, the leakage flow interacts with the main flow resulting in a change of aerodynamic losses. In this study, a 3D numerical method was used to compare endwall adiabatic cooling effectiveness values, η, and passage Total Pressure Loss Coefficients (TPLC) between a 2D contoured-endwall passage and a flat-endwall passage in a Nozzle Guide Vane (NGV) cascade using several Mass Flow Rate (MFR) values and several momentum flux ratios, I, of slot leakage flow. The numerical method was validated by comparing its computed results with experimental data, then the shape of endwall contouring was designed using an aerodynamic optimization system. The results indicate that with endwall contouring, adiabatic cooling effectiveness values on the endwall are higher than with the flat endwall for all MFR values investigated. Moreover, with the same average momentum flux ratio, I, value of leakage flow, contoured endwall and flat endwall passages show similar adiabatic cooling effectiveness distributions, especially at the regions over the upstream part of the passage, which means that η scales well with I. Over the downstream part of the passage, the contoured endwall cases show higher adiabatic cooling effectiveness values on the contoured endwall with the same average I value as used with the flat endwall passage. Over the MFR range of this study, the contoured-endwall passage shows better aerodynamic performance than that of the flat-endwall passage.
