Main Flow Reynolds Number Research Articles

Interrelationships of entropy production and turbulence kinetic energy associated with simple angle and compound angle full coverage film cooling

The present paper compares experimentally-measured distributions of entropy generation with numerically-predicted distributions of streamwise vorticity, turbulence kinetic energy, and production of turbulence kinetic energy. These comparisons are provided for two full-coverage film cooling environments which are designed to model the thermal management arrangements employed for combustor liners within gas turbine engines. One of these arrangements includes alternating compound angle values of +30° in one row of holes, followed by −30° in the next row of holes. The other arrangement includes simple angle holes with a zero degree compound angle value. The associated full-coverage film cooled boundary layers are investigated within a double-wall cooling test facility wherein the air for each full-coverage film cooling arrangement is provided by an impingement jet array. Experimentally-measured entropy generation values are obtained from film cooled boundary layer measurements of local total pressure variations, obtained in isothermal flow, relative to the freestream values outside of the boundary layer. The resulting entropy generation values quantify second law losses, which are associated with aerodynamic gains. To obtain the associated numerical-prediction results for a steady-state, three-dimensional flow field, employed is the ANSYS FLUENT Version 2022 R2 computational code with a SST k–ω turbulence closure model. The resulting comparisons of entropy generation, streamwise vorticity, turbulence kinetic energy, and production of turbulence kinetic energy are provided for a blowing ratio BR of 2.9 for simple angle film cooling with a main flow Reynolds number Rems of 138,000, and for compound angle film cooling with a main flow Reynolds number Rems of 142,000. Overall, evidence is provided of strong relationships between local turbulence kinetic energy and local entropy production since the two quantities are highly correlated with each other over s substantial range of experimental conditions and configurations. For example, ratio of turbulence kinetic energy to entropy generation data collapse for Z/de values from 0 to 3.5 for Y/de = 0.5, Y/de = 1.5, and both film cooling arrangements. Here, the value of the TKE/Sgen ratio is approximately constant for these conditions, which evidences direct and simple dependences of local turbulence kinetic energy upon local entropy generation, even for lower magnitudes of Z/de. The direct and simple dependences of local turbulence kinetic energy upon local entropy generation are further illustrated by the simplicity of linear correlation equations, which represent physical behavior for different conditions and configurations. These correlation equations are developed for three arrangements, which are associated with X/de = 54.54.

Optimizing the trench shaped film cooling design

In this numerical study an optimized trench film cooling design is determined using a Bayesian algorithm and neural network trained RANS model. Three objective functions were considered, the area-averaged film cooling efficiency, spatial standard deviation of film cooling efficiency and hot gas ingestion into the trench. Nine geometrical design parameters were varied to allow for a 3D trench shape and to find an optimal trench design based on the initial parametrization of the trench. Jet-engine like inflow boundary conditions with respect to turbulence intensity and length scales were applied. The investigated momentum ratios (I) were 1 and 8 at a main flow Reynolds number (ReD) of 2500. For each design the steady state Reynolds Averaged Navier-Stokes (RANS) equations were solved using the commercial Computational Fluid Dynamics (CFD) code Ansys Fluent V2022 R1. The turbulence model coefficients of the generalized k−ω (GEKO) model were tuned to approximate the time-averaged 3D temperature field from a predictive Large Eddy Simulation (LES) and trained by a neural network to improve the prediction capability. The tuned GEKO model shows improved agreement with experimental data of a literature case compared to the standard GEKO model. With this tuned RANS model optimized trench designs are found and validated by additional LES’s. The optimized designs include angled side walls to improve former trench designs, particularly in mitigating hot gas entrainment into the trench, which could be omitted almost entirely.

가스터빈의 연소기 냉각을 위한 이중벽 냉각 구조에서 유출 구멍의 복합각도 변경에 따른 냉각 성능 변화에 대한 수치해석적 연구

For the cooling of the combustor liner, this investigation considers a double-wall cooling structure in which the compound angle and orientation angle of the effusion hole are 30° and ±30°. respectively. Also, to analyze the effect of orientation angle, data for comparison in a simple angle configuration with an orientation angle of 0° is provided. In this study, the heat transfer and flow characteristics of the double wall cooling structure by the change in orientation angle were numerically analyzed. The results of the numerical simulations was obtained using ANSYS FLUENT V 21.1 numerical codes with a shear stress transfer k-ω turbulence model. Data are provided for main flow Reynolds numbers from 142,000 to 149,000. and overall blowing ratios from 5.5 to 7.4. The use of compound and orientation angle arrangements inhibits the formation of horseshoe-shaped vortices,BRresulting in asymmetry of the counter rotating vortex. As a result, the lift-off of the coolant injected from the effusion holes is suppressed from the effusion cooling plate. When orientation angle is changed from 0° to ± 30°, the area-averaged film cooling effectiveness and area-averaged heat transfer coefficient increase by 7.7% and 12.4% overall, respectively. The skewed and non-symmetric shape of the horseshoe-shaped vortex is also increased by the use of orientation angle arrangement, which also provide localized improvements in surface thermal protection.

Comparisons of cooling performance and flow characteristics of a combustor liner plate with compound angle and simple angle effusion holes

The present investigation considers a unique compound angle arrangement, never previously considered, with α = 30°, β = ±30°, such that the compound angle of the effusion holes changes from β = +30° to β = −30°, as adjacent rows of effusion holes are encountered. Also provided are data for comparison from a simple angle configuration with α = 30°, β = 0°. Coolant is supplied to both effusion hole arrays using arrays of impingement cooling jets. The results of the numerical simulations are obtained using the ANSYS FLUENT V 21.1 numerical code, with a shear stress transport (SST) k–ω turbulence model. Data are provided for main flow Reynolds numbers from 142,000 to 155,000, impingement flow Reynolds numbers from 7900 to 18,000, effusion flow Reynolds numbers from 10,400 to 23,600, and overall blowing ratios from 3.3 to 7.4. When β is changed from 0° to ±30°, area-averaged film cooling effectiveness values and area-averaged heat transfer coefficient magnitudes increase overall by approximately 2.89% and 11.7%, respectively. This is because the use of compound angle arrangements often inhibits the formation of the horseshoe-shaped vortex, and the resulting counter-rotating vortex legs, that often promote lift off of significant film concentrations from the test surface. The skewed and non-symmetric character of the horseshoe-shaped vortex is also increased by the use of compound angle arrangement, which also sometimes provides local improvements in surface thermal protection.

Trajectory and effectiveness of film cooling in endwall crossflow

The crossflow, one of the most important flow structures in the turbine endwall, has significant effects on the endwall film cooling. However, there is a lack of quantitative analysis on it due to the complexity of the endwall flow field. In the current study, a turning channel is utilized to generate the crossflow free from vortex structures. Experiments are conducted and numerical results are utilized to supplement flow-field details. Effects of the momentum ratio (I), crossflow intensity, and main-flow Reynolds number (ReD) are analyzed. Theories of three-dimensional boundary layer flow are introduced to help reveal underlying mechanisms. It is observed that coolant trajectories obey linearity in the cylindrical coordinate. Then, the deflection of coolant can be quantified using the straight-line slope, and I is demonstrated to well scale the coolant migration under the crossflow, which guides predictions on coolant trajectories. Reversely, the disturbance of cooling injections on the crossflow is non-negligible, mainly suppressing the crossflow development. Besides, the crossflow enhances the coolant spreading, and improves the cooling performance. ReD has non-negligible effects on the cooling performance by altering the crossflow profile in the boundary layer. Lower ReD leads to a distorted coolant spatial distribution, resulting in a severer main gas/coolant mixture.

Effect of Spanwise Hole-to-Hole Spacing on Overall Cooling Effectiveness of Effusion Cooled Combustor Liners for a Swirl-Stabilized Can Combustor

Abstract One of the most effective ways to cool the combustor liner is through effusion cooling. Effusion cooling (also known as full-coverage effusion cooling) involves uniformly spaced holes distributed throughout the combustor liner wall. Effusion cooling configurations are preferred for their high effectiveness, low-pressure penalty, and ease of manufacturing. In this article, experimental results are presented for effusion cooling configurations for a realistic swirl driven can combustor under reacting (flame) conditions. The can combustor was equipped with an industrial engine swirler and gaseous fuel (methane), subjecting the liner walls to engine representative flow and combustion conditions. In this study, three different effusion cooling liners with spanwise spacings of r/d = 6, 8, and 10 and streamwise spacing of z/d = 10 were tested for four coolant-to-main airflow ratios. The experiments were carried out at a constant main flow Reynolds number (based on combustor diameter) of 12,500 at a total equivalence ratio of 0.65. Infrared thermography (IRT) was used to measure the liner outer surface temperature, and detailed overall effectiveness values were determined under steady-state conditions. The results indicate that decreasing the spanwise hole-to-hole spacing (r/d) from ten to eight increased the overall cooling effectiveness by 2–5%. It was found that reducing the spanwise hole-to-hole spacing further to r/d = 6 does not affect the cooling effectiveness implying the existence of an optimum spanwise hole-to-hole spacing. Also, the minimum liner cooling effectiveness on the liner wall was found to be downstream of the impingement location, which is not observed in the existing literature for experiments done under nonreacting conditions.

Flow structure and surface heat transfer from numerical predictions for a double wall effusion plate with impingement jet array cooling

To provide additional understanding of double wall cooling arrangements, especially local distributions of flow properties which are responsible for hot-side surface and cold-side surface heat transfer variations, investigated are numerically-simulated distributions of turbulent flow structural characteristics. Also considered are numerically-simulated surface heat transfer characteristics, including comparisons with experimentally-measured distributions. The numerical results are obtained using the ANSYS FLUENT Version 19.1 numerical code, with a k-ω SST turbulence model. The present arrangement includes a full-coverage effusion cooling plate, with coolant initially supplied by an impingement jet array. Considered are the effects of effusion blowing ratio, impingement jet Reynolds number, and streamwise development on flow structure, and on hot-side and cold-side surface heat transfer characteristics. Data are obtained for an approximately constant main flow Reynolds number of 138000 to 159000, with blowing ratios from 2.2 to 8.5, which correspond to impingement jet Reynolds numbers from 7360 to 25200. Of particular importance are horseshoe-shaped vortices, which form upstream and around each effusion jet, which then result in two horseshoe-originated vortex legs which advect downstream along coolant trajectories. Also important are secondary flows, local flow separation regions, and local velocity regions, which are evident within the effusion hole passages near entrance locations. Within the cross flow passage, locally increased flow velocities, associated with impingement jet locations, are apparent, especially near the lower surface of the cross flow passage. These are associated with regions of augmented streamwise vorticity, which are present around the circumference of each impingement jet.

Overall Cooling Effectiveness of Effusion Cooled Can Combustor Liner Under Reacting and Non-Reacting Conditions

Abstract Emphasis on lean premixed combustion in modern low NOX combustion chambers limits the air available for cooling the combustion liner. Hence, the development of optimized liner cooling designs is imperative for effective usage of available coolant. An effective way to cool a gas turbine combustor liner is through effusion cooling. Effusion cooling (also known as full-coverage film cooling) involves uniformly spaced holes distributed throughout the liner’s curved surface area. This study presents findings from an experimental study on the characterization of the overall cooling effectiveness of an effusion-cooled liner wall, which was representative of a can combustor under heated flow (non-reacting) and lean-combustion (reacting) conditions. The model can combustor was equipped with an industrial swirler, which subjected the liner walls to engine representative flow and combustion conditions. In this study, two different effusion cooling liners with an inline and staggered arrangement of effusion holes have been studied. Non-dimensionalized streamwise hole-to-hole spacing (z/d) and spanwise hole-to-hole spacing (r/d) of 10 were used for both the effusion liners. These configurations were tested for five different blowing ratios ranging from 0.7 to 4.0 under both reacting and non-reacting conditions. The experiments were carried out at a constant main flow Reynolds number (based on combustor diameter) of 12,500. The non-reacting experiments were carried out by heating the mainstream air, and the reacting experiments were carried out under flame conditions at a total equivalence ratio of 0.65. Infrared thermography (IRT) was used to measure the liner outer surface temperature, and detailed overall effectiveness values were determined under steady-state conditions. It was observed that overall cooling effectiveness trends were different under reacting and non-reacting conditions. The cooling effectiveness for the non-reacting experiments exhibited a decreasing trend, and no consistent location of minimum cooling effectiveness was observed for the range of blowing ratios investigated in this study. For the reacting cases, the cooling effectiveness first follows a decreasing trend, reaches a distinct minimum, and then increases till the end of the combustor. Under non-reacting conditions, the staggered configuration was 9–25% more effective than inline configuration, and under reacting conditions, the staggered configuration was 4–8% more effective than inline configuration. From this study, it is clear that the coolant flame interaction for the reacting experiments impacted the liner cooling effectiveness and led to different overall cooling effectiveness distribution on the liner when compared with the non-reacting experiments.

Effects of coolant supply arrangement on double wall cooling: Hot-side effusion performance and cold-side Nusselt numbers at different initial blowing ratios

The present study considers the effects of different coolant supply arrangements on surface thermal performance for both sides of a double-wall cooled effusion plate. Supply arrangements include a cross flow only arrangement, an impingement jet array arrangement, and a combination cross flow and impingement jet array arrangement. A favorable streamwise pressure gradient is provided by a main flow passage contraction ratio CR of 4. For main flow Reynolds numbers Rems,avg of 222,000 to 233,000, four different combination values of crossflow Reynolds number and impingement Reynolds number are tested, which are associated with four different values of initial blowing ratio BR. For upstream locations along the hot-side of the effusion plate, the addition of cross flow to impingement cooling (employed with the combination cooling arrangement) often seems to degrade coolant distributions, as evidenced by adiabatic film cooling values for the cross flow/impingement combination configuration, which are often substantially lower than impingement only arrangement values. For larger x/de values, the cross flow/impingement combination behaves in a manner which is similar to the impingement only arrangement. When compared at a particular BR value, cold-side measurements show that line-averaged Nusselt number are generally highest for the impingement only configuration, and lowest for the cross flow only arrangement. Nusselt number data associated with the cross flow/impingement combination generally increase as BR increases, whereas the cross flow only data increase only slightly with initial blowing ratio.

Double wall cooling of an effusion plate with cross flow and impingement jet combination internal cooling: Comparisons of main flow contraction ratio effects

The present study considers comparisons of hot-side effusion plate results for a mainstream flow passage with CR = 1 and for a mainstream flow passage with CR = 4. The coolant supply arrangement for both CR contraction ratio values includes simultaneous use of cross flow and an impingement jet array. For the effusion cooled/hot surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). These results are given for main flow Reynolds numbers Rems of 89,900 to 95,800. For this main flow Reynolds number range, four different combination values of crossflow Reynolds number and impingement Reynolds number are tested for each CR value, which are associated with four different values of initial blowing ratio BR. With this arrangement, crossflow Reynolds number is varied, as impingement jet Reynolds number is approximately constant. The resulting variations of surface adiabatic film cooling effectiveness and surface heat transfer coefficients are due to three competing phenomena, whose relative influences change with x/de location. These include increased turbulent mixing and transport result from effusion coolant jets, decreased magnitudes of local blowing ratio with streamwise location, and significant streamwise acceleration, which induces local boundary layer re-laminarization. When the CR = 4 arrangement is employed, these phenomena result in dramatic decreases of local and line-averaged heat transfer coefficients, and local and line-averaged adiabatic film effectiveness magnitudes, with streamwise development, for x/de > 60. Resulting values are then significantly lower than when CR = 1, provided comparisons are made at a particular streamwise location for each value of initial blowing ratio BR.

Experimental Investigation of Heat Transfer in Cavities of Steam Turbine Casings Under Generic Test Rig Conditions

This paper presents the first experimental results of the systematic investigation of forced convection heat transfer in scaled generic models of steam turbine casing side spaces with varied geometric dimensions under fully turbulent air flow. Data were obtained by two redundant low-heat measuring methods. The results from the steady-state inverse method are in good agreement with the data from the local overtemperature method, which was applied via a novel miniaturized heat transfer coefficient (HTC) sensor concept. All experiments were conducted at the new side space test rig “SiSTeR” at TU Dresden. The dependencies of the HTC distributions on the axial widths of the cavity and its inlet and on the eccentricity between them were investigated for Reynolds numbers from Re=40,000 to 115,000 in the annular main flow passage. The measured HTC distributions showed a maximum at the stagnation point where the induced jet impinges on the wall surface, and decreasing values toward the cavity corners. Local values scaled roughly with the main flow Reynolds number. The HTC distributions thereby differed considerably depending on the dimensions and the form of the cavity, ranging from symmetric T-shape to asymmetric L-shape, with upstream or downstream shifted sidewalls.

Double Wall Cooling of a Full-Coverage Effusion Plate With Main Flow Pressure Gradient, Including Internal Impingement Array Cooling

The present study provides new effusion cooling data for both the surfaces of the full-coverage effusion cooling plate. For the effusion-cooled surface, presented are spatially resolved distributions of surface adiabatic film cooling effectiveness and surface heat transfer coefficients (measured using transient techniques and infrared thermography). For the impingement-cooled surface, presented are spatially resolved distributions of surface Nusselt numbers (measured using steady-state liquid crystal thermography). To produce this cool-side augmentation, impingement jet arrays at different jet Reynolds numbers, from 2720 to 11,100, are employed. Experimental data are given for a sparse effusion hole array, with spanwise and streamwise impingement hole spacing such that coolant jet hole centerlines are located midway between individual effusion hole entrances. Considered are the initial effusion blowing ratios from 3.3 to 7.5, with subsonic, incompressible flow. The velocity of the freestream flow which is adjacent to the effusion-cooled boundary layer is increasing with streamwise distance, due to a favorable streamwise pressure gradient. Such variations are provided by a main flow passage contraction ratio CR of 4. Of particular interest are effects of impingement jet Reynolds number, effusion blowing ratio, and streamwise development. Also, included are comparisons of impingement jet array cooling results with: (i) results associated with crossflow supply cooling with CR = 1 and CR = 4 and (ii) results associated with impingement supply cooling with CR = 1, when the mainstream pressure gradient is near zero. Overall, the present results show that, for the same main flow Reynolds number, approximate initial blowing ratio, and streamwise location, significantly increased thermal protection is generally provided when the effusion coolant is provided by an array of impingement cooling jets, compared to a crossflow coolant supply.

Double Wall Cooling of a Full Coverage Effusion Plate With Cross Flow Supply Cooling and Main Flow Pressure Gradient

Experimentally measured results are presented for different experimental conditions for a test plate with double wall cooling, composed of full-coverage effusion-cooling on the hot side of the plate, and cross-flow cooling on the cold side of the plate. The results presented are different from those from past investigations, because of the addition of a significant mainstream pressure gradient. Main stream flow is provided along a passage with a contraction ratio of 4, given by the ratio upstream flow area, to downstream flow area. With this arrangement, local blowing ratio decreases significantly with streamwise development along the test section, for every value of initial blowing ratio considered, where this initial value is determined at the most upstream row of effusion holes. Experimental data are given for a sparse effusion hole array. The experimental results are provided for mainstream Reynolds numbers of 92,400–96,600, and from 128,400 to 135,000, and initial blowing ratios of 3.3–3.6, 4.4, 5.2, 6.1–6.3, and 7.3–7.4. Results illustrate the effects of blowing ratio for the hot side and the cold side of the effusion plate. Of particular interest are values of line-averaged film cooling effectiveness and line-averaged heat transfer coefficient, which are generally different for contraction ratio of 4, compared to a contraction ratio of 1, because of different amounts and concentrations of effusion coolant near the test surface. In regard to cold-side measurements on the crossflow side of the effusion plate, line-averaged Nusselt numbers for contraction ratio 4 are often less than values for contraction ratio 1, when compared at the same main flow Reynolds number, initial blowing ratio, and streamwise location.

Internal and external cooling of a full coverage effusion cooling plate: Effects of double wall configuration and conditions

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal boundary conditions, after mainstream flow conditions are established. For the effusion cooled surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). For the coolant side, presented are spatially-resolved distributions of surface Nusselt numbers (measured using liquid crystal thermography). Of interest are the effects of streamwise development, blowing ratio, and Reynolds number. Streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) on the effusion plate are 15 and 4, respectively. Effusion hole diameter is 6.35 mm, effusion hole angle is 25°, and effusion plate thickness is 3 hole diameters. Considered are overall effusion blowing ratios from 2.9 to 7.5, with subsonic, incompressible flow, and constant freestream velocity with streamwise development, for two different mainstream Reynolds numbers. For the hot side (mainstream) of the effusion film cooling test plate, results for two mainflow Reynolds numbers of about 145000 and 96000 show that the adiabatic cooling effectiveness is generally higher for the lower Reynolds number for a particular streamwise location and blowing ratio. The heat transfer coefficient is generally higher for the low Reynolds number flow. This is due to altered supply passage flow behavior, which causes a reduction in coolant lift-off of the film from the surface as coolant momentum, relative to mainstream momentum, decreases. For the coolant side of the effusion test plate, Nusselt numbers generally increase with blowing ratio, when compared at a particular streamwise location and mainflow Reynolds number.

Numerical prediction of cooling losses in a high-pressure gas turbine airfoil

Numerical investigations of the flow past a film-cooled nozzle guide vane cascade were conducted to determine the influence of coolant ejection on profile loss. The film cooling on the suction surface as well as the trailing edge bleeding was simulated at engine representative main flow Reynolds and Mach numbers, varying the coolant ejection rate. Experiments carried out in a high-speed wind tunnel provided a comprehensive test case to verify the capability of the numerical models to correctly reproduce the flow phenomena taking place in the vane passage. Results show that the main features of the flow, such as aerodynamic loading, flow separation, and loss distribution in the wake of the airfoil can be quite accurately predicted without excessive computational effort using a standard RANS SST model, which proved to be a reliable and more adequate alternative to the widely used models based on simple control volume analysis.

Mixing performances of swirl flow and corrugated channel reactors

Four different geometrical solutions for tubular reactors are compared for transfer intensification in fluid processes: (1) a compact multi-tube with helical screw-tape inserts, (2) a plain corrugated channel with a smooth bend curvature, called “wavy channel”, (3) a plain corrugated channel with a herringbone pattern, called “zigzag channel”, and (4) a plain straight pipe serving as the reference case. The single-phase mixing abilities of these four devices are compared by the chemical probe method (Villermaux/Dushman iodide/iodate system) for a range of main-flow Reynolds numbers between 100 and 4000. The chemical probe method is used here to investigate the global mixing time in the entire reactor volume, as deduced from the segregation index by a phenomenological model. Experimental results reveal better mixing performance and reduced energy expenditures in the helical-insert tube, in both the laminar and turbulent regimes.

Experimental study of heat and mass transfer of a rolling wheel

Heat transfer characteristics of a rolling wheel are investigated by using the naphthalene sublimation technique. The local and average Nusselt numbers are obtained. The results reveal that the local and average Nusselt numbers increase with increasing rotating Reynolds number. Under the same rotating Reynolds number they decrease along the radius direction. After comparing with similar available cases reported, it is found that the results are very close to the results of rotating disk in crossflow under the condition that rotating Reynolds number is equal the main flow Reynolds number.

STUDYING EFFECTS OF INJECTED FLOW ON DRAG COEFFICIENTS OVER SEMI PERFORATED CIRCULAR CYLINDER

The secondary flow forced into primary flow through wall holes (injection flow) has numerous uses in industry as an example film cooling. Injection flow is also a way of controlling characteristic of boundary layer flow. In this work, an experimental study has been pereformed to investigate the influence of injection flow rate, the main flow Reynolds number and the orientation (front, top or rear) of injected flow on velocity profile behind a half holed circular cylinder. Based on measured velocity profile, the drag coefficient has been calculated and presented. The results show that, the injected flow affects characteristic of the flow over the cylinder and change the velocity profile behind the cylinder. Comparing with a cylinder without injection, the drag coefficient values show a drop in value for the case where the flow is injected in rear of the cylinder. For the case where the flow injects through top of the cylinder, generally the drag coefficient is still lower and for the case where the flow is injected at the front of the cylinder, the drag coefficient could be lowered for some combination value of the injected flow rate and the main flow Reynolds number.DOI: http://dx.doi.org/10.5755/j01.mech.19.2.4147

Cross-Injection Film Cooling on a Curved Surface with or without a Vortical Flow in the Mainstream

Liquid crystal thermography with steady-state experimental method is used to investigate the effectiveness of two-row, cross-injection film cooling on a concave or convex surface. One leg of vortices of a delta wing is used to realize the interaction mechanism between the vortex generated by the cross-injection coolant and the secondary vortex of the main flow. The secondary flow generated by the delta-wing vortex generator produces upwash or downwash motion when sweeping over the film injection holes. In the experiments, the cooling hole diameter, hole-to-hole distances, and an included angle of 120 degrees are fixed, while the main flow Reynolds number, sense of mainstream vortex, and the coolant-to-main flow blowing ratio are varied. Because the cross-injection coolant generates a counter-clockwise vortex (viewed from upstream), results show that when the mainstream vortex has a sense of rotation opposite to that of the cross-injection vortex (i.e. an upwash mainstream vortex), the effectiveness is increased. On the other hand, same sense of rotation in both vortices (i.e. a downwash mainstream vortex) decreases the effectiveness. Both the convex and concave curvatures hamper the attachment of cross-injection coolant to the surface, resulting in a reduction in film cooling effectiveness. The effect is more influential for the concave surface.

Control of the Separation Flow in a Sudden Enlargement

In the present paper, an experimental and numerical investigation of fluid flow and heat transfer in the case of wall injection besides main flow through a circular sudden enlargement are studied. The injected flow is achieved through an annular slot placed around the inner side wall of the step. The static pressure variation along the sudden enlargement length is measured and calculated at different values of injection ratio ( Q ) and injection flow angles. The average heat transfer with Reynolds number (ReJ) of injected flow at different values of the inlet flow angle is obtained. The velocity, turbulent kinetic energy and temperature contours are presented in this study. Reynolds number of injected flow is varied between 320 and 840, Reynolds number of main flow is between 5895 and 8450 and the injection flow angles are 0 o , 15 o , 30 o , 45 o and 60 o . In the injection case, the results indicate that, the pressure recovery coefficient increases by decreasing the injection ratio and increasing the flow angle. The average heat transfer coefficient increases as both injection Reynolds number and the injection flow angle increase. The numerical results showed that two recirculation zones generate behind the step between the injection flow and the main flow. The size of these recirculation zones decreases by increasing the injection flow rate. The turbulent kinetic energy increases within region between the recirculation zones and main zone also, it decays by injecting flow in the recirculation zone. The length for higher value of flow temperature decreases by injecting flow in the recirculation zone, and that length increases as the injection flow rate increases. The comparison between the experimental results and the numerical results gives good agreement using the k-e model with Leschziner and Rodi correction.