Endwall Secondary Flow Research Articles

Loss Mechanism of Low-Pressure Turbine Secondary Flows Due to Different Incoming Boundary Layers

Abstract In high bypass ratio engines, the flow exits the interturbine duct (ITD) and enters the low-pressure (LP) turbine. This paper aims to understand the effects of the boundary layer at the exit of ITD on the endwall secondary flows and loss of the first blade row in a low-pressure turbine. From the Navier–Stokes equations, the loss is decomposed into the parts generated by the mean vortex as well as turbulence theoretically. The result of computational fluid dynamics (CFD) shows that the incoming boundary layer from the ITD increases the total pressure loss coefficient by 14% compared to the case with uniform inlet condition. Although the distribution of the secondary vortices is strongly affected by the inlet boundary layer, the loss generated by the mean vortex within the blade passage is hardly affected. The analysis based on the turbulent dissipation shows that the dominant factor leading to the loss increase is the turbulent dissipation downstream of the blade trailing edge (TE) near the hub. The mixing process of the wake and the strong counter-rotating vortex pair (CVP) increases the turbulent dissipation significantly. It is also found that a simplified incoming boundary layer defined by the Prandtl's one-seventh power law can not reproduce the complex effects of the incoming boundary layer from the ITD.

Numerical investigation on flow and heat transfer characteristics of vortex cooling in an actual film-cooled leading edge

This paper numerically investigates the flow and heat transfer characteristics of vortex cooling in an actual film-cooled leading edge. Two internal vortex cooling cases called Case P and Case S are involved in this study. Case P means that the coolant injection nozzles are arranged near the pressure surface side of the blade, and Case S means that the coolant injection nozzles are arranged near the suction surface side. The mainstream region and the swirl chambers of the vortex cooling cases are connected by 6 rows of film holes. Results indicate that the practical mainstream flow generated by the actual blade affects the vortex flow structures and brings about an endwall secondary flow. For internal vortex cooling, the large-scale vortex flow structures in Case P skew off while flow structures in Case S are not distinctly influenced. Two type of flow regimes form near the film hole due to the suction effect, and bring about different local heat transfer augmentation intensity. For film cooling, the endwall secondary flow forces the coolant film move towards or away from the endwall thus decreases the film cooling efficiency. The film hole blowing ratio distribution is affected due to the different influence of mainstream flow on internal vortex flow of Case P and Case S, which results in different film cooling efficiency distribution. The film cooling efficiency of Case S on the pressure surface increases by up to 59.8% compared with Case P.

Unsteady experimental and numerical investigation of aerodynamic performance in ultra-high-lift LPT

Detailed experimental and numerical investigations were performed for an ultra-high-lift front-loaded low-pressure turbine cascade (Zw = 1.58) with periodic wakes. The interaction mechanisms between the incoming wakes and endwall secondary flow were carefully examined. Wakes were produced by moving upstream rods, and flow field downstream of the cascade was measured using a seven-hole probe. Experimental results revealed that incoming wakes influenced not only the boundary layer development of the blade suction surface but also the complex endwall secondary vortex structures. On the suction surface: Incoming wakes clearly suppressed the suction side separation bubble at a low Reynolds number of 25000. Nevertheless, the effects of different wake passing frequencies were not significantly different at Re = 100000, and the profile losses under wake passing were even greater than in the absence of wakes. At the endwalls: Incoming wakes more strongly suppressed secondary flow at Re = 100000 than at Re = 25000, because the low-momentum fluid inside the incoming wakes clearly increased the endwall cross-passage pressure gradient at Re = 25000. The experimental results indicated that periodic wakes decreased the passage vortex and counter vortex core strength by 25% and 30%, respectively, at Re = 100000. Instantaneous results also demonstrated that endwall secondary vortices decreased significantly near the position of wakes passing.

Unsteady wakes-secondary flow interactions in a high-lift low-pressure turbine cascade

Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine (LPT) cascade. All of the measurements were conducted in both the presence and absence of incoming wakes, and numerical analysis was performed to elucidate the flow mechanism. With increasing Reynolds number, the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers, leading to a lower blade loading near the leading edge and suppression of the Pressure Side (PS) leg of the horseshoe vortex. However, the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side (SS) separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers. Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000. In contrast, at the high Reynolds number of 100,000, the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes, and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.

Influences of large fillets on endwall flows in a vane cascade with upstream slot film-cooling

Investigations in cascade employ filleted blades to influence the near endwall secondary flows and total-pressure losses. The secondary flows aggravate the aerodynamic losses and endwall thermal stresses in the gas turbine passages. Investigations of different configurations of the slot-bleed flow from the endwall of cascade upstream show significant influences on the near endwall flows. In the present paper, the near endwall flow-field in a linear cascade employing filleted vanes and bleed flow from the upstream endwall slots is measured experimentally. Two fillet profiles are tested, one is larger than the other. The objectives are to quantify the combined effects of endwall fillet, fillet profiles, and film-cooling flow on the endwall region flow-field. The fillet covers the junction of vane and endwall upstream of the cascade throat region. The discontinuous bleed-slots near the cascade entrance provide the film-cooling flow on endwall and simulate the gaps between combustor/nozzle-vane discs or stator/rotor discs in the gas turbine. The inlet Reynolds number of 2.0E+05 is based on the chord length of vane profile. The density and temperature ratios of the coolant flow to mainstream are both about 1.0. The inlet blowing ratio of the film-cooling flow varies between 1.0 and 2.8. The flow-field is measured through the distributions of flow temperature, yaw angle, axial vorticity, and total-pressure losses along the vane passage. The effects on the flow-field are then presented by comparing the cases of filleted vanes with the cases of un-filleted vanes. The results of flow yaw angle and axial vorticity in the filleted passage are smaller than those in the passage without the fillet. The yaw angles responsible for the endwall secondary flows are the smallest for the smaller fillet (Fillet-2). The temperature field indicates the pitchwise distributions of the coolant on endwall specially near the pressure side are better when the smaller fillet is employed. Also, the weakened passage vortex of the endwall secondary flows in the filleted passage reduces the total-pressure losses. Although the total-pressure losses decrease at very high coolant mass flux with and without the fillet, the losses are always smaller for the filleted passage than for the un-filleted passage. The present investigation is beneficial for improving and optimizing the endwall film-cooling in the gas turbine passage.

The effect of endwall boundary layer and incoming wakes on secondary flow in a high-lift low-pressure turbine cascade at low Reynolds number

The endwall flow features are heavily dependent on the incoming boundary layer. It was particularly important to increase understanding the effect of inlet boundary layer thickness on endwall secondary flow under unsteady conditions. In present study, the influences of incoming wakes and various boundary layer thickness on endwall secondary flow were studied in a typical high-lift low-pressure turbine cascade, numerical calculation and experiment measurement of seven-hole probe were adopted at Re = 25,000 (based on the inlet velocity and the axial chord). Upstream wakes were simulated through moving rods upstream of the cascade. Detailed analysis was focused on the mechanisms of periodic wake influencing on the endwall vortex structures under thick endwall boundary layer condition. Influences of two different endwall boundary layer thickness on endwall secondary vortices structures were also comparatively analyzed. Under steady condition without wake, although thick incoming boundary layer reduces the cross-passage pressure gradient near endwall, more low momentum fluid inside thick endwall boundary layer is drawn into secondary vortices, finally resulting in stronger the pressure side leg of the leading edge horseshoe vortex and passage vortex, compared to the results of thin boundary layer condition. Under unsteady condition with thick inlet boundary layer, the “negative jet” effect of incoming wakes delays intersection of pressure side leg and suction side leg of leading edge horseshoe vortex on blade suction surface. The time-averaged strength of passage vortex and counter vortex core decreases by about 32%, and the underturning and overturning of endwall secondary flow is suppressed. The instantaneous results also indicate the endwall secondary vortices are reduced periodically at the position of wakes passing.

Effect of periodic wakes and a contoured endwall on secondary flow in a high-lift low-pressure turbine cascade at low Reynolds numbers

The use of a contoured endwall has the potential to suppress endwall secondary flow. Unsteady wakes affect not only the boundary layer characteristics of blade suction surface at blade midspan but also the endwall flow structures. The lack of understanding of the flow mechanism of the combined effects of periodic wakes and contoured endwall on secondary flow limits their roles. This paper presents a experimental and numerical investigation of the endwall secondary flow in a typical high-lift low-pressure turbine cascade. Wakes were produced by moving rods upstream of cascade, and the flow fields at the exit of cascade were measured using a seven-hole pressure probe. The study focused on the combined effect of the upstream wakes and the contoured endwall on the secondary flow as well as the underlying physical mechanisms. The influences of the Reynolds numbers and the contoured endwall on the performance of high-lift low-pressure turbine endwall regions were also discussed. At steady conditions without wakes, the total losses in the turbine cascade increased with decreasing Reynolds number; the most intense passage vortex, counter vortex and corner vortex were observed at a low Reynolds number of 25,000 (based on the axial chord and the inlet velocity). The contoured endwall decreased the cross-passage pressure gradient, and suppressed the passage vortex. Under unsteady conditions, the interaction between upstream wakes and the passage vortex results in reduction of the passage vortex. The combined effect of the contoured endwall and periodic wakes redistributed the endwall pressure and further decreased the cross-passage pressure gradient. Consequently, the intensities of the passage vortex and counter vortex decreased by 17% and 11% respectively, compared with the flat endwall cascade with wakes. Contoured endwall with wakes reduced secondary kinetic energy of cascade exit by 53.8% than the result of the flat endwall no wake. Which is beneficial to improve the aerodynamic performance of the high-lift low-pressure turbine.

Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5×106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward-facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely, Nusselt number, was derived. This paper also presents a comparison with computational fluid dynamics (CFD) predictions performed by solving the steady-state Reynolds-averaged Navier–Stokes with Reynolds stress model using the commercial CFD solver ansysfluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25% to 0% span), and five backward-facing, upstream step geometries (step heights from 0% to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient (HTC) level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the HTC (by ∼10% to 40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3–1.3%) because of the forward-facing upstream step geometry but is slightly reduced (by 0.1–0.3%) by the presence of the backward upstream step geometry.

Application of endwall contouring in a high-subsonic tandem cascade with endwall boundary layer suction

A proper combination of active and passive flow control methods would be a promising way to further enhance the compressor performance. This numerical investigation presents a new attempt of application of endwall contouring in a high subsonic tandem cascade with the endwall boundary layer suction implemented in the forward blade. The study aims to further improve the corner flow in the rear blade at design and lower incidences. The planar endwall is redesigned using the optimization method. Nonuniform rational B-spline surface is employed to parameterize the endwall surface. A multi-points optimization strategy is selected to minimize the aerodynamic loss generated in the cascade. In the optimization, the suction strategy remains unchanged. To clarify the impacts of endwall contouring on the cascade performance, flow details in both mainflow passage and suction flow path at design and off-design incidences are analyzed.As a result, the total loss decreases by 8.4% at the design incidence via the endwall contouring. Furthermore, a more prominent loss reduction can be achieved at lower incidences. However, the control effects of endwall contouring is weakened towards higher positive incidences. Worse still, even a deterioration in the cascade performance can be detected at I=5° due to the presence of a small-scale corner stall in the forward blade. The results indicate that, as the gap flow is not strong enough to counteract the endwall secondary flow, the endwall contouring could be employed to further enhance the flow control ability of the previous proposed compound flow control method, while its negative impact on the cascade performance at higher positive incidences still remains to be addressed.

Influence of the pressure side injection slot on the cooling performance of endwall surface

ABSTRACTIn modern gas turbine engines, the first stage vane endwall endures high thermal load with the increase of the turbine inlet temperature and the uniformity of the temperature distribution at combustor outlet. Moreover, the endwall secondary flow forces the coolant flow toward the suction side, resulting in hot regions along the pressure side endwall. In the worst case, hot regions lead to thermal failure. In order to ensure that the gas turbine operates safely, advanced cooling techniques are urgently needed to be implemented to reduce the hot regions along the pressure side endwall. In the current research, the influences of the pressure side injection slot on the film cooling performance of the endwall surface were numerically investigated. The three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations combined with the shear stress transport (SST) turbulence model were solved to conduct the simulations. Cases with different injection slot configurations have been simulated. The results indicate that the hot region along the pressure side endwall is significantly reduced by introducing the pressure side injection slot. The coolant from the pressure side injection slot is assisted by the pressure side vertical flow toward the adjacent vane suction side. Therefore, the coolant coverage and the cooling effectiveness are increased. In this study, the expanded slot (ES) achieves a larger cooling effectiveness than the normal slot (NS) and convergent slot (CS) at a small blowing ratio M = 0.5. In contrast, the CS obtains a larger cooling effectiveness than the NS and ES at M = 1.0 and M = 1.5. In addition, the introduction of the pressure side injection slot has a small influence on the aerodynamic performance of the vane cascade.

The nonaxismmetric endwall aerodynamic optimization design for a large turbine cascade with a midgap

The nonaxisymmetric endwall has been verified to be an effective method in reducing the endwall secondary flow loss. Some assembly features, such as the midgap in the hub of real aircraft engines, may have an influence on the endwall secondary flow. In the present work, a nonaxisymmetric endwall with midgap structure is designed for a large linear turbine cascade. A nonaxisymmetric endwall optimization design procedure is developed to minimize the total pressure loss coefficient at the passage exit. The profile of the endwall is designed using automatic numerical optimization with the Kriging surrogate method. The numerical simulation based on a transition shear stress transport model is used as the aerodynamic evaluation tool for the optimization system. When the midgap is considered in the design, mixing loss between midgap flows and main flow is significantly reduced. However, the loss relative to the passage vortex is increased to some extent.

Large Eddy Simulation and CDNS Investigation of T106C Low-Pressure Turbine

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100,000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot–Savart Law.

Secondary flow control using endwall jet fence in a high-speed compressor cascade

This paper proposes a secondary flow control concept using Endwall jet fence (EJF). A parametric investigation concerning the variations of the jet location along the axial and pitch-wise direction as well as the skew angle is conducted numerically to validate the potential of EJF in a high-speed compressor cascade with an inlet Mach number of 0.67. And then the interaction mechanisms between the EJF and the endwall secondary flow are discussed in detail. The results show that the EJF could reduce the corner separation and losses significantly by inputting transverse momentum component, inducing a concentrated jet vortex to block the pitch-wise migration of the passage vortex as well as enhancing the energy exchange between the endwall boundary layer and the mainstream. The jet location and the skew angle are important for the influence of EJF on the cascade performance. In this work, a maximum total pressure loss reduction of 11.6 % is obtained by the EJF located at 30 % of the axial chord and 10 % of the pitch with a skew angle of β = 40°, whereas the jet-to-inflow mass flow ratio is only about 0.4 %, validating the high efficiency of this flow control concept. For the off-design points, the EJF also shows appreciable potential on the endwall secondary flow control and loss reduction.

Experimental and Computational Study of the Effect of Momentum-Flux Ratio on High-Pressure Nozzle Guide Vane Endwall Cooling Systems

High-pressure (HP) nozzle guide vane (NGV) endwalls are often characterized by highly three-dimensional (3D) flows. The flow structure depends on the incoming boundary layer state (inlet total pressure profile) and the (static) pressure gradients within the vane passage. In many engine applications, this can lead to strong secondary flows. The prediction and design of optimized endwall film cooling systems is therefore challenging and is a topic of current research interest. A detailed experimental investigation of the film effectiveness distribution on an engine-realistic endwall geometry is presented in this paper. The film cooling system was a fairly conventional axisymmetric double-row configuration. The study was performed on a large-scale, low-speed wind tunnel using infrared (IR) thermography. Adiabatic film effectiveness distributions were measured using IR cameras, and tests were performed across a wide range of coolant-to-mainstream momentum-flux and mass flow ratios (MFRs). Complex interactions between coolant film and vane secondary flows are presented and discussed. A particular feature of interest is the suppression of secondary flows (and associated improved adiabatic film effectiveness) beyond a critical momentum flux ratio. Jet liftoff effects are also observed and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to 3D, steady-state computational fluid dynamics (CFD) simulations. This paper provides insights into the effects of momentum flux ratio in establishing similarity between cascade conditions and engine conditions and gives design guidelines for engine designers in relation to minimum endwall cooling momentum flux requirements to suppress endwall secondary flows.

Effects of periodic wakes on the endwall secondary flow in high-lift low-pressure turbine cascades at low Reynolds numbers

Periodic wakes affect not only the surface boundary layer characteristics of low-pressure turbine blades and profile losses but also the vortex structures of the secondary flow and the corresponding losses. Thus, understanding the physical mechanisms of unsteady interactions and the potential to eliminate secondary losses is becoming increasingly important for improving the performance of high-lift low-pressure turbines. However, few studies have focused on the unsteady interaction mechanism between periodic wakes and endwall secondary flow in low-pressure turbines. This paper verified the accuracy of computational fluid dynamics by comparing experimental results and those of the numerical predictions by taking a high-lift low-pressure turbine cascade as the research object. Discussion was focused on the interaction mechanisms between the upstream wakes and secondary flow within the high-lift low-pressure turbine. The results indicated that upstream wakes have both positive and negative effects on the endwall flow, where the periodic wakes can decrease significantly the size of the separation bubble, prevent the formation of secondary vorticity structures at relatively high Reynolds numbers (100,000 and 150,000), and reduce the cross-passage pressure gradient of cascade. In addition, periodic wakes can improve the cascade incidence characteristic in terms of reducing the overturning and underturning of the secondary flow at downstream of the cascade all of which are beneficial for decreasing the endwall secondary losses, whereas more endwall boundary layer is involved in the main flow passage due to the wake transport, resulting in increased strength of the secondary flow at low Reynolds number of 25,000 and 50,000. Compared with the results without wakes, the total pressure loss for unsteady condition at the cascade exit decreases by 2.7% and 6.1% at high Reynolds number of 100,000 and 150,000, respectively. However, the secondary loss at unsteady flow conditions increases at low Reynolds number of 25,000 and 50,000.

Endwall Secondary Flow Control in Low Pressure Turbine

Endwall Secondary Flow Control in Low Pressure Turbine

Effects of vortex generator jet on corner separation/stall in high-turning compressor cascade

The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall control are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that the corner separation could be reduced significantly, which results in a wider operation range as well as a more uniform exit flow angle and total pressure profile. At the near-stall operation point, the maximum relative reduction of the total pressure loss is up to 32.5%,, whereas the jet mass ratio is less than 0.4%,. Based on the analysis of the detailed flow structure, three principal effects of the VGJ on the endwall cross flow and corner separation are identified. One is to increase the tangential velocity component opposite to cross flow, thus inhibiting the endwall secondary flow near the jet exit. The second is to suppress the pitchwise extension of the passage vortex as an air fence. The third is to sweep the low energy fluids towards the mainstream on the up-washed side and to transport the mainstream fluids to the endwall to reenergize the boundary layer on the down-washed side.

Reduction of endwall secondary flow losses with leading-edge fillet in a highly loaded low-pressure turbine

A detailed experimental and numerical investigation of the effect of leading-edge fillet on the endwall secondary flow was performed in a highly loaded low-pressure turbine cascade. The objective is to gain further understanding on the reduction mechanism of endwall secondary flow losses by leading-edge fillet. The results suggest that the numerical results offer a reliable prediction for the endwall secondary flow structure together with suction surface separation bubble. A pressure-side corner separation vortex is found in the front part of pressure surface/endwall junction, where an inverse flow goes upward and over the leading edge to suction side of the same blade. This inverse flow also takes part in the interaction between endwall secondary flow and separation bubble. However, the leading-edge fillet can fill the region of corner separation vortex, and the inverse flow is eliminated. Combined with the reduction of cross-pressure gradient achieved by this fillet, the loss coefficient and flow angle deviation at exit plane are decreased. Besides, the leading-edge fillet will reduce the intensity of leading-edge horseshoe vortex and thus decrease the loss of passage vortex and shed vortex. It is these three aspects introduced by leading-edge fillet that achieves an effective reduction of the endwall secondary loss in turbine.

Application of Riblets on Turbine Blade Endwall Secondary Flow Control

Within the past 10 years, significant improvements have been achieved in the laser manufacturing process. It is feasible now to design various small-scale surface features (such as dimples, riblets, grooves, etc.) in gas turbine applications with the current manufacturing readiness level of laser surface texturing techniques. In this paper, the potential of adding riblets on a turbine endwall has been investigated through combined computational fluid dynamics and experimental studies in a low-speed linear cascade environment. Detailed comparisons of the flow structures have been made for cases with and without riblets on the endwall. The numerical results show that endwall riblets can effectively reduce the strength of the pressure side leg of the horseshoe vortex, lower the cross-passage pressure gradient, and alleviate the lift up of the passage vortex. Oil film flow visualization and exit aerodynamic loss survey in experiments support the computational fluid dynamics observations: The passage vortex loss core moves closer to the endwall with the addition of riblets. The present study consistently demonstrates that the addition of riblets can be an effective approach to reduce the endwall secondary flow. Further research questions are raised for the applicability of the riblets concept in actual engine conditions and options for design optimization.

Multi-row film cooling characteristics on a vane endwall

The secondary flow vortices make the flow field near the endwall highly three-dimensional. The jet-to-secondary flow interaction and the interaction between multiple film rows are important for the understanding of endwall film cooling characteristics and the improvement of prediction method. Single row film cooling, three combinations of two-row film cooling as well as a full coverage configuration with five rows of film cooling on a typical flat vane endwall with matched averaged blowing ratios and density ratio to the engine condition were investigated experimentally. Detailed measurements of adiabatic film cooling effectiveness distribution using PSP technique as well as the pressure distribution of the endwall were performed. The single row film cooling results were used to test the applicability of the superposition law on the prediction of endwall multi-row film cooling effectiveness compared to the multi-row experimental results. The results indicated that the superposition method could not give quantitatively reliable film cooling effectiveness of the endwall multi-row cases especially for the full coverage film cooling configuration. The upstream film injections could alter the endwall secondary flow and affect the coolant spreading of the downstream row. Moreover the interaction between the downstream and upstream injections increased the mixing loss and induced a higher turbulence level which made the coolant from the upstream row dissipate faster.