Coolant Crossflow Research Articles

Effect of the Key Geometry and Flow Parameters on Discharge Coefficient of Laidback Fan-Shaped Hole Under Coolant Crossflow Condition

Abstract A laidback fan-shaped hole is commonly used due to its superior lateral film coverage. Its discharge coefficient is significantly influenced by internal crossflow owing to its complex geometrical structure. In this paper, the authors numerically investigate the flow mechanisms of the laidback fan-shaped hole under the influence of internal crossflow. The numerical simulations utilize the validated SST k–ω turbulence model, with the Reynolds number of internal crossflow ranging from 20,000 to 160,000 and the ratio of pressure ranging from 1 to 1.6. The results show that the different orientations of internal crossflow cause varying degrees of in-hole separation that led to a discrepancy in the discharge coefficient. The larger the Reynolds number of the crossflow is, the more drastic the change in the discharge coefficient. Furthermore, a comparison between the results obtained with and without internal crossflow has shown that the length of the cylindrical section is the primary factor determining the discharge coefficient of the laidback fan-shaped hole. The magnitude of the discharge coefficient depended on the extent of flow separation within the cylindrical section. Additionally, the numerical simulations obtained the discharge coefficient under a high internal crossflow Reynolds number of internal crossflow and a wall with a constant thickness and compared it with the predictions of a low-dimensional model of the discharge coefficient (based on our previous experimental data). The discrepancy between the results is within 10%, thus verifying the scalability of the low-dimensional model.

A coupled vibration model of double-rod in cross flow for grid-to-rod fretting wear analysis

In Pressurized Water Reactors, most of the failed fuel rods are often observed at the periphery of the fuel assembly, especially near the core baffle. The rod vibration-induced fretting wear is a significant failure mechanism strongly correlated with the coolant and support conditions. This paper presents a coupled vibration model of double-rod to predict the grid-to-rod fretting (GTRF) wear. A motion-dependent fluid force model is used to simulate the coolant cross flow, the gap constraints with asymmetric stiffness between spring and dimple on the vibration form, and the fretting wear are discussed. The results show the effect of the coupled vibration on the deterioration of wear, providing a sound theoretical explanation of some failure phenomena observed in the previous experiment. Exploratively, we analyze the impact of the baffle jet on the GTRF wear, which indicates that the high-velocity cross-flow will significantly affect the vibration forms while sharply changing the wear behavior.

A comprehensive heat transfer investigation for impingement/effusion cooling under crossflow conditions

Impingement/effusion cooling is regarded as a highly efficient cooling structure and has been widely adopted in various energy-dependent scenarios. It often exhibits crossflow phenomena due to design or concurrent factors. However, quantifying the individual heat transfer contributions of each cooling structure in impingement/effusion cooling under crossflow conditions remains unclear. In this study, the pressure-sensitive paint and temperature-sensitive paint techniques were adopted to separately evaluate the performance of effusion and impingement cooling under crossflow conditions for a comprehensive heat transfer investigation. Different coolant flow rate (normalized as Rejet = 10,000 to 25,000) and crossflow flow rates (normalized as CMR = 0 to 0.3) were examined. In effusion cooling, cooling effectiveness generally decreased with higher Rejet but improved with increased CMR, except for Rejet = 10,000 and 15,000 with CMR ≥ 0.25, where excessive crossflow coolant negatively affected cooling effectiveness. When comparing cooling effectiveness at the same blowing ratio, higher Rejet with crossflow consistently outperformed, with the maximum improvement reaching 11.55 %. In impingement cooling, the Nusselt number (Nu) increased with Rejet due to enhanced impingement momentum. Crossflow had a detrimental effect at Rejet = 10,000 but showed improvements at Rejet = 15,000 to 25,000. With increasing Rejet, heat transfer performance became less sensitive to varying CMR. Compared to cases without crossflow, the Nu increments at CMR = 0.25 were -5.01 %, 4.03 %, 3.53 %, and 2.64 % for Rejet = 10,000 to 25,000, respectively. It was revealed that crossflow was influential on the impingement cooling, meanwhile, highly influential on the effusion cooling. This study intended to provide a more comprehensive understanding of impingement/effusion cooling and assistance in designing more efficient and tailored cooling strategies for high-performance energy systems.

Sensitivity of Laidback Fan-Shaped Hole Discharge Coefficient Under Internal Coolant Crossflow Conditions

Abstract An experimental study was performed on the discharge coefficients of laidback fan-shaped holes under different internal coolant crossflow orientations. The influence of the geometric and flow parameters on the discharge coefficient was investigated under flat plate conditions, where the pressure ratio ranged from 1 to 1.6. The results show that the film hole discharge coefficient is more sensitive to variations in the coolant crossflow under small pressure ratios. In comparison, the discharge coefficient is much less sensitive to the change of coolant crossflow under high pressure. Meanwhile, the length of the cylindrical section varied over the range of 1D–4D, and the length of the expansion section varied from 2D to 6D, where D represents the diameter of the film hole. The results show that the discharge coefficient is much more sensitive to the length of the cylindrical section than to the length of the expansion section. To quantify the sensitivity of the internal crossflow effects on the discharge coefficient, a low-ordered reduced model is proposed for the discharge coefficient of laidback fan-shaped holes. Both the geometric and flow parameters are considered in the model and give prediction errors within 5%.

Large eddy simulation of film cooling flow from diffusion slot hole with crossflow coolant configuration

A three-dimensional compressible large eddy simulation (LES) method was performed to explore the flow and heat transfer characteristics in the hole and mixing zone of a crossflow film cooling model. A traditional cylindrical hole and diffusion slot hole were selected as the cases for the film hole. The characteristics of the crossflow film flow-field and the influence of the internal crossflow on the film cooling of the diffusion slot hole were explained by the vortex flow in the hole and the instantaneous/time-averaged jet mixing. The results showed that helical motion is easily induced in the holes under the influence of crossflow. Asymmetric outlet flow behavior is the main reason for the asymmetric characteristics downstream of the hole. The difference in the blowing ratio results in the difference in the strength of the spiral vortex and the central vortex tube inside the hole. For the diffusion slot hole, the high-speed zone caused by the crossflow effect at the hole-inlet gradually evolves into strip shapes under the combined action of axial extrusion and spanwise diffusion. With the disappearance of the helical structure, the high-speed areas gradually converge on both sides of the hole exit in the span direction, and the streamline at the exit develops relatively smoothly. The inlet crossflow and the crossflow Reynolds number have little effect on the film cooling effectiveness of the diffusion slot hole. With an increase in the blowing ratio, the lateral diffusion capacity of the film is gradually enhanced. Furthermore, compared with the cylindrical hole, the instantaneous film fluctuation region of the diffusion slot hole case is smaller in range and more symmetrical in distribution. These findings advance the understanding of the film cooling of diffusion slot holes.

Comparisons on flow characteristics and film cooling performance of cylindrical and sister holes with/without internal coolant crossflow

Simulations and comparisons on the influence of internal coolant crossflow of a novel film cooling hole design, called “sister holes”, and a baseline cylindrical hole were performed with an established turbulence model. The results show that sister holes can provide better film cooling performance than the baseline case at three blowing ratios, and as the blowing ratio increases the sister holes show significant advantages. At a high blowing ratio, the simple cylindrical hole provides very poor cooling effectiveness, since the jet penetrates into the passage flow due to the high jet velocity and the action of a counter-rotating vortex pair. Compared with the cases using a plenum feeding the film cooling holes, the cases with internal coolant crossflow show higher laterally-averaged film cooling effectiveness because deflection of the jet is caused by the crossflow.

Large eddy simulation of internal coolant crossflow orientation effects on film-cooling effectiveness of fan-shaped holes

In modern gas turbine engines, the coolant is typically injected through the small cooling holes on the surface of the blade using an internal crossflow. Most experimental and numerical studies have used a stagnant plenum to feed the cooling holes without considering the influence of the internal coolant crossflow orientation. Therefore, in this study, we used large eddy simulations (LES) to investigate the effect of internal coolant crossflow orientations on film-cooling effectiveness and turbulent flow structures of fan-shaped cooling holes. A 7-7-7 laidback fan-shaped hole with an injection angle of 30-degree located on a flat plate surface was selected as a reference case. Three different internal coolant crossflow orientations (parallel/perpendicular with respect to the mainstream flow) were numerically conducted at a density ratio (DR) of 1.5 and two different blowing ratios (M = 1.5 and 3.0). The computational data were validated by the measurements of the reference case with a stagnant plenum in terms of flow and thermal fields. At both blowing ratios, the coolant channel parallel to the mainstream flow direction showed the best cooling performance among the cases. The coolant channel perpendicular to the mainstream flow displayed the minimum area-averaged film-cooling effectiveness, with a reduction of about 17% compared to the stagnant plenum. The velocity-field analysis showed an asymmetric pattern inside the cooling hole for the perpendicular coolant channel case due to the cooling hole entrance effect, which affects the distributions of film-cooling effectiveness on the flat plate. Furthermore, the time-space assessment of the velocity-field revealed greater flow unsteadiness and a wavy pattern for the crossflow perpendicular to the direction of coolant injection.

Effect of Coolant Crossflow on Film Cooling Effectiveness of Diffusion Slot Hole With and Without Ribs

Abstract The coolant flow condition at the film hole entrance has a notable effect on film cooling effectiveness. The previous studies about internal ribbed crossflow effects are the hole with a circular inlet cross section. In this study, a diffusion slot hole with a race-track inlet cross section is examined in a low-speed wind tunnel by the pressure-sensitive paint (PSP) technique. The film cooling effectiveness of three different hole configurations are investigated: a normal diffusion slot hole, a compound angle diffusion slot hole, and a lateral inclination angle diffusion slot hole. Two internal perpendicular crossflow conditions with and without ribs for the 45 deg inline crossflow and the 135 deg counter crossflow are discussed. The blowing ratios are varied from 0.5 to 2.5 at a constant crossflow-to-mainstream velocity ratio of 0.36. A detailed method for the uncertainty analysis of the PSP is also presented. It is found that the normal diffusion slot hole always shows the best cooling performance than other holes. The ribs under the crossflow condition have a positive effect on the film cooling effectiveness for the normal diffusion slot hole even though the compound angle changes the hole’s orientation. However, the ribs have a negative effect on the film cooling effectiveness for the geometrically asymmetric diffusion slot hole.

Cooling holes with different structures effects on coolant cross flow and heat transfer at the outlet of the combustion chamber

Abstract: The major effects of cylindrical and row trenched cooling holes with angles of alpha=30, beta=0, alpha=40, beta=0 and alpha=50, beta=0 at BR=3.18 on the effectiveness of film cooling near the combustor end wall surface is an important subject to study in detail. In the current study, researchers used a FLUENT package 16/11 to simulate a 3-D model of a Pratt and Whitney gas turbine engine. In this research, RNG turbulence model K-ε model was used to analyze the flow behavior on the passage ways of internal cooling. In the combustor simulator, the dilution jets and cooling flow staggered in the streamwise direction and aligned in the spanwise direction as well. In comparison with the baseline case of cooling holes, the application of trenched hole near the end wall surface increased the effectiveness of film cooling up to 100% for different trench cases.

Film cooling performance for the cratered film-cooling holes with various coolant crossflow orientations

The present study investigates the influence of the coolant crossflow orientation on the cooling performance for the cratered film-cooling hole. It is well known that the quiescent coolant plenum is mostly adopted in the laboratory for convenience. In the present article, the coolant crossflow channels with three possible orientations in practice are further considered. The flow fields for the film-cooling are solved with the RANS method with the SST turbulence model at blowing ratios of 0.5, 1.0, and 2.0. The numerical results show that the coolant crossflow orientation significantly alters the coolant flow at the hole exit, further the downstream vortex structure and the cooling effectiveness. The symmetric flow and cooling effectiveness distribution occur for the quiescent plenum case, in-line parallel crossflow case, and the counter parallel crossflow case provide, but the asymmetrical flow and cooling effectiveness distribution for the perpendicular crossflow. The in-line parallel crossflow case gives almost considerable cooling effectiveness as the common quiescent plenum case. On the other hand, the counter-parallel crossflow case provides the worst cooling performance due to the opposite flow direction of the coolant supply relative to the mainstream flow. At the high blowing ratio of 2.0, the cooling performance is higher for the perpendicular crossflow feeding despite its asymmetrical distribution of the cooling effectiveness.

Time-Accurate Evaluation of Film Cooling Jet Characteristics for Plenum and Crossflow Coolant Supplies

Abstract Gas turbine film cooling creates complicated and highly unsteady flow structures. This study seeks to examine the unsteady characteristics created by different cooling hole inlet geometries using a fast-response pressure-sensitive paint (PSP) technique able to capture time-accurate measurements at 2000 frames per second, resolving frequencies up to 1000 Hz. Time-accurate and time-averaged measurements are used to evaluate the performance of a plenum-style inlet and a crossflow-style inlet in varying turbulence environments over a flat plate. The results of this study are intended to begin the process of breaking down widely accepted time-averaged film effectiveness trends into the cumulative effects of freestream turbulence and momentum flux ratio, with emphasis on the cooling jet motions they cause. Jet behaviors observed in this study include a sweeping oscillation, unsteady attachment and separation from the plate, and time-accurate and time-averaged flow bias. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. Crossflow-fed cooling holes show bias to the upstream side of the cooling hole with respect to the internal crossflow direction. Plenum-fed cooling holes outperform crossflow-fed cooling holes, and the difference grows with increasing momentum flux ratio. The frequency of both plenum- and crossflow-fed cooling jet motions is influenced by the freestream turbulent velocity fluctuations. The resulting mode shapes show dominant side-to-side sweeping for higher turbulence environments and a separation and reattachment motion for lower turbulence environments. At higher momentum flux ratio, the jets were seen to increasingly favor separation and reattachment motions. The results of this study are intended to better inform existing predictive tools. With a better understanding of the time-accurate behaviors responsible for creating the commonly accepted time-averaged coolant distributions, simple predictive tools may be better equipped to accurately model film cooling flows.

Numerical Investigations of Film Cooling Characteristics of Interrupted Slot and Trench Holes on a Vane Endwall

This paper describes film cooling characteristics of the novel combined configuration employing interrupted slot and trench holes on a vane endwall. Interrupted slot, formed by uneven thermal expansion between combustor and high-pressure turbine vane, can improve adiabatic film cooling effectiveness of the leading edge and pressure side-endwall junction by inhibiting the development of horseshoes vortex. Holes embedded into a straight trench were introduced to improve film efficiency comparing to cylindrical holes on vane passage endwall. The influences of lateral pressure gradient, slot coolant and step on crossflow of the hole coolant in trench were mainly discussed. Three dimensional Reynolds-averaged Navier-Stokes equations with shear stress turbulence model (SST k-ω) were used to obtain the flowfields and adiabatic film cooling effectiveness of a cascade model. Four hole blowing ratios M=0.5, 1.0, 1.5, 2.0 and two axial positions X/Cax= −0.05, 0 were considered. The coolant crossflow in trench on flat endwall of cascade passage trends to flow towards suction side due to the lateral pressure gradient rather than both sides on flat plate. For combined configuration of interrupted slot and trench holes, the step vortex rolls up hole coolant upstream of trench which changes η distributions comparing to that on flat passage endwall. Comparing to the cylindrical holes, better film cooling performance can still be obtained when arranging trench holes under high blowing ratios. The influence of hole’s axial positions was also discussed.

Film cooling characteristics of cross-flow coolant passage with various relative positions of holes and inclined ribs

To investigate the application of ribbed cross-flow coolant channels with film hole effusion and the effects of the internal cooling configuration on film cooling, experimental and numerical studies are conducted on the effect of the relative position of the film holes and different orientation ribs on the film cooling performance. Three cases of the relative position of the film holes and different orientation ribs (post-rib, centered, and pre-rib) in two ribbed cross-flow channels (135° and 45° orientation ribs) are investigated. The film cooling performances are measured under three blowing ratios by the transient liquid crystal measurement technique. A RANS simulation with the realizable k-ε turbulence model and enhanced wall treatment is performed. The results show that the cooling effectiveness and the downstream heat transfer coefficient for the 135° rib are basically the same in the three position cases, and the differences between the local effectiveness average values for the three are no more than 0.04. The differences between the heat transfer coefficients are no more than 0.1. The “pre-rib” and “centered” cases are studied for the 45° rib, and the position of the structures has little effect on the film cooling performance. As the film hole moves backward relative to the rib position (from the pre-rib to the post-rib), the swirling flow formed in the hole has a slight difference, and the discharge coefficient of the film hole increases slightly at lower blowing ratio while decreases slightly at higher blowing ratio. In the different position cases, the outlet velocity distribution of the film holes, the jet pattern and the discharge coefficient are consistent with the variation in the cross flow.

Discharge coefficients and aerodynamic losses for cylindrical and cratered film-cooling holes with various coolant crossflow orientations

In addition to cooling performance, the discharge coefficient, and aerodynamic loss should be considered to apply the film-cooling hole to the modern gas turbine blade's cooling design. The present study describes the discharge coefficients and aerodynamic loss characteristics for cylindrical and cratered holes with a numerical method. The shear stress transport turbulence model is firstly validated in comparison with the literature data. The discharge coefficients, total pressure coefficients, mixing pressure coefficients, and hole pressure coefficients are further determined under the coolant channel outlet's static pressure. The flow fields and velocity distributions of three coolant crossflow orientation configurations, including the co-flow orientation, the counter-flow orientation, and the perpendicular-flow orientation, are analyzed and compared. The numerical results show that the cratered hole always yields a higher discharge coefficient than the cylindrical hole, especially under the low-pressure ratio. The discharge coefficient is highly sensitive to the coolant crossflow orientation, mainly caused by the different separation flow at the hole entrance. The perpendicular-flow orientation configuration has the medium value of the discharge coefficient. For aerodynamic loss valuation, the cratered hole has a higher total pressure loss coefficient and pressure loss coefficient in the hole, but lower mixing pressure loss coefficient. The coolant flow orientation also influences these three pressure loss coefficients for the cylindrical hole and cratered hole, which can be explained by analyzing the flow field around the hole exit.

Film cooling performance evaluation of the furcate hole with cross-flow coolant injection: A comparative study

Turbine blades are consistently exposed to high-temperature gas in an effort to increase the maximum efficiency of gas turbine engines. Therefore, a growing need exists to protect the outer surfaces from high-temperature gas. Film cooling has long been used as an active thermal protection scheme, and the shaped film-hole is one possible solution to the aforementioned problem. Based on the actual coolant supply channel of the turbine blades, the film cooling performance of a novel furcate hole fed by cross-flow coolant injection with 135-deg ribs was experimentally investigated in this study. The Reynolds numbers of the main-flow and cross-flow are 10,000 and 100,000, respectively, and the blowing ratio M ranges from 0.5 to 2.0. The adiabatic film effectiveness η and heat transfer coefficient of the furcate hole are obtained by the transient liquid-crystal measurement technique, and a detailed comparison between the furcate hole and cylindrical hole geometries, simple and compound hole, is presented. The results show that the span-wise width of the film coverage is significantly more comprehensive than that of the compound hole due to the configuration of the span-wise expansion for the furcate hole. At a lower M, the film coverage gradually narrows, and the η gradually decreases along the flow direction for the furcate hole. The heat transfer enhancement of the furcate hole is the highest among the studied cases, and the heat transfer uniformity is much impoverished. With an increasing M, the advantages of the high η of the furcate hole are gradually revealed. The degree of deflection of the film coverage gradually increases toward the +Y side. Both the effectiveness and magnitude of the span-wise η are improved at M=1.0. At a larger M of 2.0, the heat transfer enhancement is the weakest, and the heat transfer uniformity is improved. The net heat-flux reduction is introduced to comprehensively evaluate the cooling performance. The values of the traditional holes invariably decrease as M increases, whereas that of the furcate hole first increases and then decreases. As M increases to 1.0 and 2.0, the comprehensive benefits of the furcate hole become more apparent.

Effect of internal coolant crossflow on the film cooling performance of converging slot hole

The effect of crossflow Reynolds number on the film cooling characteristics was investigated on low speed flat-plate facility. The film cooling performance was measured by transient liquid-crystal technique and the flow feature was obtained by numerical simulation. Two film hole cases, converging slot hole case and cylindrical hole case, were carried out at two crossflow Reynolds numbers, Rec = 50,000 and 100,000 and three blowing ratios, M = 0.5, 1.0 and 2.0. For cylindrical hole, high Reynolds number deteriorates the film cooling effectiveness at blowing ratio of 0.5. However, better film coverages are observed at M = 1.0 and 2.0. At each blowing ratio, high crossflow Reynolds number produces higher heat transfer for cylindrical hole case. The converging slot hole case presents better film coverage in whole region. The film cooling effectiveness and heat transfer are not sensitive to the crossflow at each blowing ratio. Discharge coefficients of two holes are increased as increasing of blowing ratio, while the high crossflow Reynolds number deteriorates the discharge of flow. The numerical results indicate that the different performance of film cooling between two kinds of holes at crossflow condition is mainly attributed to the different development of in-tube vortex.

Investigation of Coolant Local Hydrodynamics in the Mixed Core of the VVER Reactor

The article presents the results of experimental studies of the local hydrodynamics of the coolant flow in the mixed core of the VVER reactor, consisting of the TVSA-T and TVSA-T mod.2 fuel assemblies. Modeling of the flow of the coolant flow in the fuel rod bundle was carried out on an aerodynamic test stand. The research was carried out on a model of a fragment of a mixed core of a VVER reactor consisting of one TVSA-T segment and two segments of the TVSA-T.mod2. The flow pressure fields were measured with a five-channel pneumometric probe. The flow pressure field was converted to the direction and value of the coolant velocity vector according to the dependencies obtained during calibration. To obtain a detailed data of the flow, a characteristic cross-section area of the model was selected, including the space cross flow between fuel assemblies and four rows of fuel rods of each of the TVSA fuel assemblies. In the framework of this study the analysis of the spatial distribution of the projections of the velocity of the coolant flow was fulfilled that has made it possible to pinpoint regularities that are intrinsic to the coolant flowing around spacing, mixing and combined spacing grates of the TVSA. Also, the values of the transverse flow of the coolant caused by the flow along hydraulically nonidentical grates were determined and their localization in the longitudinal and cross sections of the experimental model was revealed. Besides, the effect of accumulation of hydrodynamic flow disturbances in the longitudinal and cross sections of the model caused by the staggered arrangement of hydraulically non-identical grates was determined. The results of the study of the coolant cross flow between fuel assemblies interaction, i.e. between the adjacent TVSA-T and TVSA-T mod.2 fuel assemblies were adopted for practical use in the JSC of “Afrikantov OKB Mechanical Engineering” for assessing the heat engineering reliability of VVER reactor cores; also, they were included in the database for verification of computational hydrodynamics programs (CFD codes) and for detailed cell-based calculation of the reactor core.

Experimental and Numerical Investigations on the Heat Transfer of Film Cooling With Cylindrical Holes Fed With Internal Coolant Cross Flows

Abstract The heat transfer coefficient of cylindrical holes fed by varying internal cross-flow channels with different cross-flow Reynolds numbers Rec is experimentally studied on a low-speed flat-plate facility. Three coolant cross flow cases, including a smooth case and two ribbed cases with 45/135-deg ribs, are studied at Rec = 50,000, and 100,000 with varying blowing ratios M of 0.5, 1.0, and 2.0. A transient liquid-crystal (LC) measurement technique is used to determine the heat transfer coefficient. At lower M, the heat transfer enhancement regions are asymmetrical for the smooth and 45-deg cases. The asymmetrical vortex is more pronounced with increasing cross-flow direction velocity, resulting in a more skewed distribution at Rec = 100,000. Conversely, the contours are laterally symmetric in the 135-deg case at varying Rec. A fork-shaped trend with a relatively high heat transfer coefficient appears upstream, and the increases in the heat transfer in the 135-deg cases are lower than those in the 45-deg cases. As M increases to 2.0, the vortex intensity increases, resulting in a stronger scouring effect upstream, especially at large Rec. The range and degree are affected by Rec at M = 2.0. The core of the heat transfer enhancement is skewed to the −Y side for both cases.

Baffle jetting: CFD analysis of plain jets impinging on fuel rods

The risk of baffle jetting exists mainly in pressurized water reactors, which are designed with a counter flow configuration in the core bypass region. Baffle plates are foreseen between core barrel and core, providing the core's lateral restraint and allowing a core bypass flow. A pressure differential establishes between the coolant flow in the core baffle and the upward flow through the core. A part of the coolant bypass flow is directed through the gaps of the baffle plates towards the core. Coolant cross flow through enlarged baffle gaps can result in high velocity jetting in the case of significant pressure differences between core and baffle region. These water jets impact onto the fuel rods and may induce rod vibration that can lead to fuel rod failure.Modelling baffle jetting induced vibrations of fuel rods is still a challenge in the field of fluid structure interaction. The present work aims to extend the understanding of the unsteady flow in rod bundles to situations where baffle jetting occurs. As a first step, the used LES modelling method is evaluated on the example of a well documented test case related to fuel rods in cross flow: the flow over a circular cylinder at Re = 3900. In the successive step, the validated modelling method is applied to the CEA PANACHET experiment, mimicking baffle jetting related phenomena. This analysis helped to understand better the flow field of a corner baffle jet and further validated the modelling approach.The flow field in the core baffle corner is finally analysed for realistic reactor conditions. A plain narrow slot jet is injected parallel to a baffle wall through a 1 mm width gap perpendicular to the axial flow of a corner assembly. The analysis of the flow field showed that: (i) Swirling flow exist close to the corner rod. The calculated force coefficients lift and drag of this rod show a dominant fluctuation frequency of about 80 Hz. (ii) The baffle jet impacts on the third rod in jet direction (passing the first two rods without impact). The force coefficients of the third rod do not show a dominant oscillation frequency but show increased oscillation amplitudes. The distinguished fluctuation frequency detected for rod n°1 and the direct impact of the baffle jet on rod n°3 might explain the rod failures that have been detected for these rods.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.