Impingement Holes Research Articles

Effect of Jet-to-Jet Distance and Pipe Position on Flow and Heat Transfer Features of Active Clearance Control Systems

Abstract The goal of this work is to investigate the effect of supply pipe position on the heat transfer features of various active clearance control (ACC) geometries, characterized by different jet-to-jet distances. All geometries present 0.8 mm circular impingement holes arranged in a single row. The jets generated by such holes cool a flat target surface, which is replicated by a metal plate in the experimental setup. Measurements are performed using the steady-state technique, obtained by heating up the target plate thanks to an electrically heated Inconel foil applied on the side of the target opposite to the jets. Temperature is also measured on this side by means of an IR camera. Heat transfer is then evaluated thanks to a custom-designed finite difference procedure, capable of solving the inverse conduction problem on the target plate. The effect of pipe positioning is studied in terms of pipe-to-target distance (from 3 to 11 jet diameters) and pipe orientation (i.e., rotation around its axis, from 0 deg to 40 deg with respect to target normal direction), while the investigated jet Reynolds numbers range from 6000 to 10,000. The obtained results reveal that heat transfer is maximized for a given pipe-to-target distance, dependent on both jet-to-jet distance and target surface extension. Pipe rotation also affects the cooling features in a nonmonotonic way, suggesting the existence of different flow regimes related to jet inclination.

Experimental and Numerical Studies on the Enhanced Heat Transfer Performance and Flow Resistance Characteristics of the Double-Wall Cooling Structure with Jet Impingement Holes and Pin Fins

Experimental and Numerical Studies on the Enhanced Heat Transfer Performance and Flow Resistance Characteristics of the Double-Wall Cooling Structure with Jet Impingement Holes and Pin Fins

Detailed velocity and heat transfer measurements of an advanced insert for impingement cooling

This work reports the results of paired experiments for the aft section of a complex internal cooling flow within a gas turbine vane using Magnetic Resonance Velocimetry (MRV) and steady-state Infrared (IR) thermography. The aft cooling insert for the vane with two-pass impingement was designed at a scale five times larger than the original and built using stereolithography (SLA) fabrication methods. The MRV technique was used to measure the three-dimensional, three-component velocity field for a test case with a Reynolds number range of 2,600 to 7,600 based on diameter of the impingement holes. Flow distribution, impingement hole performance, and cross flow effects are discussed for the experiment in which a dilute aqueous copper sulfate solution was used as the working fluid. A paired experiment with a geometrically similar design employed electrical heating of a thin stainless steel shim to model a constant heat flux boundary condition of an interior wall of the turbine vane. The modeled vane insert was then operated with air as the working fluid at two test conditions with Reynolds numbers in the range of approximately 1,200 to 7,600 based on the diameter of the impingement holes. An IR camera was used to measure the surface temperature of the shim. Using energy balances and the known heat flux, the temperature data were used to determine heat transfer characteristics of the impinging jets for the pressure and suction side surfaces, including the Nusselt number. The MRV and IR data sets provide detailed insight into the surface effects of the flow distribution and the result on the local and area-averaged heat transfer performance. A strong coupling between the velocity field and temperature data provide insight into design feature performance, and serve as a validation data set for matched computational simulations. Finally, a comparison with internal heat transfer correlations is presented using the data from Florschuetz et al. [1]. The results showed a lack of agreement with Florschuetz, leading to the development of a novel methodology for estimating the heat transfer performance of an impinging hole with crossflow. Measurement uncertainty was estimated to be ±5% for velocity and ±5% for the spatially averaged Nusselt number distributions.

Effect of an impinging jet on the flow characteristics and thermal performance of mainstream in battery cooling of hybrid electric vehicles

The novel concept of impinging jet cooling, i.e., an active-passive air cooling strategy, was proposed to achieve improved battery thermal management in hybrid vehicles, and this method is supported by excess high pressure discharged air. To comprehensively realize the active-passive combined cooling behavior, a rectangular channel with a jet impingement hole was utilized to experimentally and numerically study the flow characteristics and thermal performance of the joint cooling mechanism. The numerical results were confirmed by the experimental data in this work, the maximum deviations of the offset and Nusselt numbers are 18.8% and 7.5%, respectively. The thermal transport performs much better under the interaction between the mainstream and impinging jet, i.e., the average Nusselt number and maximum Nusselt number can be increased by 0.43-16.55, 5.73-34.42, respectively, at inlet pressures of the impinging jet in the range of 1–6 bar. The values of Nu/Nu0/(f/f0) 1/3 are improved by 1.52–3.33. The jet fluid was deflected under the influence of the mainstream and a vortex can be induced, which is beneficial for the heat transfer performance. The jet fluid closely reached the heated plane at a relatively large volume flow rate and the heat transfer performance was excellent once the jet fluid touched the heated plane. The thermal boundary layer becomes thinned under the impact of the impinging jet but the magnitude of the reduction is relatively slight.

Improvement of Multi-Hole Airflow Impingement on Flow and Heat Transfer Characteristics Inside a Turbine Vane Cavity

The cooling effect of turbine vane is of great importance for ensuring thermal protection and economic operation of gas turbines. This study aims to reveal the influence mechanism and performance of impingement cooling and heat transfer within a turbine guide vane cavity. Then, a turbine guide vane cavity with a complex pin fins structure is numerically investigated at a multi-hole impingement by comparison with experiment verification. The results show that the larger the Reynolds number is, the larger the average Nusselt number is on the upper and lower surfaces of the cavity. The average Nusselt number increased on the upper and lower surfaces as the impingement hole diameter increased. Comparing 1 impingement hole with 16 ones, the average Nusselt number of the lower surface of the latter is 553.9% larger than that of the former. Furthermore, the average Nusselt number of the lower surface for pin fin height of 3 mm is only improved by 11.2% for pin fin height of 24 mm. The heat transfer effect near the impingement holes is better than that far away from the impingement holes. In particular, it is recommended to have 14 impingement holes with a hole diameter of 7.2 mm, as well as circular pin fins with a height of 3 mm and spacing of 25.8 mm. In addition, the entropy generation distribution in impingement cooling is analyzed. This study can provide a reference to enhance the turbine vane cooling performance by optimization design.

Thermal and centrifugal stresses in curved double wall transpiration cooled components with temperature dependent thermoelastic properties

The integration of double wall transpiration cooling (DWTC) into gas turbines and hypersonic vehicles is key for addressing future needs in aerospace and power generation. This paper identifies the roles of geometric curvature and temperature dependence of thermoelastic properties on stresses in DWTC systems under combined thermal and centrifugal loading. An increase of thermal expansion coefficient, α, with temperature as exhibited by Ni alloys is shown to dominate over the decrease of Young’s modulus, E, in double walls, such that the thermal stresses are significantly higher than the case of temperature independent E and α. The effect is generally promoted by the thermal mismatch between the walls; in highly curved systems, the difference in wall circumferences also comes into play. The critical stresses at film holes, impingement holes and pedestals are affected differently for systems with convex and concave hot outer surfaces while the optimal wall thickness ratio is suggested to depend on the severity of thermal loading with respect to centrifugal loading. Our elastic solutions provide the essential information for evaluating the structural integrity of DWTC systems and can be generalised to multiwall systems.

Experimental Study of Impingement Effusion Cooled Double-Wall Combustor Liners: Aerodynamic Analysis with Stereo-PIV

A new experimental study is presented for a combustor with a double-wall cooling design. The inner wall at the hot gas side features effusion cooling with 7-7-7 laidback fan-shaped holes, and the outer wall at the cold side features an impingement hole pattern with circular holes. Data are acquired to asses the thermal and aerodynamic behavior of the setup, using a new, scaled up, engine similar test rig. Similarity includes Reynolds, Nusselt and Biot numbers for hot gas and coolant flow. Different geometrical setups are studied by varying the cavity height between the two walls and the relative alignment of the two hole patterns at two different impingement Reynolds numbers. This article focuses on the aerodynamic performance of the setup. Instationary flow data are acquired, using a high speed stereo PIV setup. For each geometrical configuration, approximately 20 planes are recorded with a data rate of 1000 Hz by traversing the flow region of interest in the cavity between the two specimen. This fine resolution allows the reconstruction of 3D flow fields for the mean data values and an extensive analysis of transient phenomena at each plane. Time averaged data and jet-center plane transient data are presented in detail. The results show a complex flow field with a hexagonal vortex pattern in the cavity, which is mainly influenced by the cavity height and the relative alignment of the two walls. The jet Reynolds number shows small influence when analyzing normalized data. Small cavity heights show a less developed flow field with less stable vortex systems. The alignment shows a similar influence on vortex system stability, with the aligned case performing better. Additionally, statistical analysis of the jet flow and frequency domain analysis of the jet and the effusion flow are presented, showing the damping capability of the cavity, especially at increased cavity heights, and a residual low frequency pulsation of the effusion cooling inflow.

Experimental Study of Impingement Effusion-Cooled Double-Wall Combustor Liners: Thermal Analysis

A new experimental study is presented for a combustor with a double-wall cooling design. The inner wall at the hot gas side features effusion cooling with 7-7-7 laidback fan-shaped holes, and the outer wall at the cold side features an impingement hole pattern with circular holes. Data have been acquired to assess the thermal and aerodynamic behavior of the setup using a new, scaled up, engine-similar test rig. Similarity includes Reynolds, Nusselt, and Biot numbers for hot gas and coolant flow. Different geometrical setups are studied by varying the cavity height between the two walls and the relative alignment of the two hole patterns at several different blowing ratios. This article focuses on the thermal performance of the setup. The temperature data are acquired using two infrared systems on either side of the effusion wall specimen. In addition to cooling effectiveness evaluations, finite element simulations are performed, yielding the locally resolved wall heat fluxes. Results are presented for three cavity heights and two longitudinal specimen alignments. The results show that the hot gas side total cooling effectiveness can achieve values as high as 90% and is mainly influenced by the effusion coverage. Impingement cooling has a small influence on overall effectiveness, and the area of influence is mainly located upstream where effusion cooling is not built up completely. The analyzed geometric variations show a major influence on cavity flow and impingement heat transfer. Small cavities lead to constrained flow and high local Nusselt numbers, while larger cavities show more equalized Nusselt number distributions. A present misalignment shows especially high influence at small cavity heights. The largest cavity height, in general, showed a decrease in heat transfer due to reduced jet momentum.

Experimental Investigation of Micro Cooling Units on Impingement Jet Array Flow Pressure Loss and Heat Transfer Characteristics

With the development in additive manufacturing, the use of surface treatments for gas turbine design applications has greatly expanded. An experimental investigation of the pressure loss and heat transfer characteristics within impingement jet arrays with arrays of target surface micro cooling units is presented. The discharge coefficient and Nusselt number are measured and determined for an evaluation of the pressure loss of the flow system and heat transfer level, respectively. Considered are effects of impingement jet Reynolds number ranging from 1000 to 15,000 and micro cooling units (square pin fin) height (h) with associated values of 0.01, 0.02, 0.05, 0.2, and 0.4 D, where D is the impingement hole diameter. Presented are variations of Nusselt number, and Nusselt number ratio, discharge coefficient, discharge coefficient ratio, discharge coefficient correlation. Depending upon the micro cooling unit height, discharge coefficient ratios slightly decrease with height, and the ratio values generally remain unit value (1.0). When Rej = 1000 and 2500 for several cooling units height values, discharge coefficient ratios show the pressure loss decreases about 2–18% and 3–6%, respectively, when compared to the data of a baseline smooth target surface plate. The observed phenomenon is due to the effects of flow blockage of micro cooing units, local flow separation, and near-wall viscous sublayer reattachment. Results also show that heat transfer levels increase 20–300% for some of the tested toughened target surface plates when compared to smooth target surface plates. The heat transfer level enhancement is because of an increase in thermal transport and near-wall mixing, as well as the increased wetted area. In addition, micro cooling units elements break the viscous sublayer and cause greater turbulence intensity when compared to the smooth target surface. Overall, results demonstrate that the target surface micro cooling units do not result in a visible increment in pressure loss and reduce pressure loss of the flow system for some of the tested patterns. Moreover, results show the significant ability of micro cooling units to enhance the surface heat transfer capability of impingement cooling relative to smooth target surfaces.

Multiscale analysis of thermomechanical stresses in double wall transpiration cooling systems for gas turbine blades

Double wall transpiration cooling (DWTC) is a new technology that allows the gas turbine inlet temperatures to be increased beyond current levels to promote higher engine efficiency. DWTC systems consist of outer hot and inner cooler walls, connected by pedestals, which contain film cooling and impingement holes, respectively. In order to employ these new systems, an evaluation of the stresses that drive fatigue and ratchetting at critical stress raisers is essential. We present a modelling framework which combines Computational Fluid Dynamics (CFD)-heat transfer solutions for the temperature field in DWTC systems, with theoretical and Finite Element (FE) elastic solutions for the thermal (T) stress and centrifugal (CF) stress fields. We demonstrate that uniaxial tensile CF loading causes much higher stress concentration factors (SCF) at cooling holes and wall-connecting pedestals than the thermally induced biaxial stresses. A theoretical framework is developed, supported by FE studies, that captures the dependence of the SCF on important geometric parameters, such as wall thicknesses, pedestal height and hole size, spacing and inclination angle, which provides important information for the optimisation of these systems. A key observation of relevance to both conventional and non-conventional turbine blade designs, is that the superposition of tensile CF stresses to compressive T stresses is beneficial for the performance at the critical film hole features; for double wall blades, however, the superposition degrades the performance at impingement holes and pedestals, as in these locations the T stresses are also tensile. These stresses can be balanced by using an optimal wall thickness ratio. Our elastic solutions can be readily used in analyses for predicting structural ratchet boundaries based on shakedown theory and the local cyclic strain range that drives thermomechanical fatigue in DWTC systems.

A Comparison of Single-Entry and Multiple-Entry Casing Impingement Manifolds for Active Thermal Tip Clearance Control

In this paper, we compare using computational fluid dynamics the aero-thermal performance of two candidate casing manifolds for supplying an impingement-actuated active tip clearance control system for an aero-engine high-pressure turbine. The two geometries are (a) single-entry: an annular manifold fed at one circumferential location; (b) multiple-entry: a casing manifold split into four annular sectors, with each sector supplied separately from an annular ring main. Both the single-entry and multiple-entry systems analysed in this paper are idealised versions of active clearance control systems in current production engines. Aero-thermal performance is quantitatively assessed on the basis of the heat transfer coefficient distribution, driving temperature difference for heat transfer between the jet and casing wall and total pressure loss within the high-pressure turbine active clearance control system. We predict that the mean heat transfer coefficient (defined with respect to the inlet temperature and local wall temperature) of the single-entry active clearance control system is 77% greater than the multiple-entry system, primarily because the coolant in the multiple-entry case picks up approximately 40 K of temperature from the ring main walls, and secondarily because the average jet Reynolds number of impingement holes in the single-entry system is 1.2 times greater than in the multiple-entry system. The multiple-entry system exhibits many local hot and cold spots, depending on the position of the transfer boxes, while the single-entry case has a more predictable aero-thermal field across the system. The multiple-entry feed system uses an average of 20% of the total available pressure drop, while the feed system for the single-entry geometry uses only 2% of the total available pressure drop. From the aero-thermal results of this computational study, and in consideration of holistic aero-engine design factors, we conclude that a single-entry system is closer to an optimal solution than a multiple-entry system.

Effects of Cooling Configurations on the Aerothermal Performance of a Turbine Endwall With Jet Impingement and Film Cooling

Abstract With the increase of turbine inlet temperature and the application of premixed combustion, turbine components, particularly the turbine endwall, work in a harsh environment and must be effectively cooled to ensure the component durability. Recently, new cooling schemes that employ both external film cooling and internal jet impingement cooling have drawn much attention due to their extraordinary performance. In this study, a numerical model of turbine endwall with jet impingement and film cooling was established and validated against the experiment. To investigate the effects of geometric parameters related to this cooling scheme, four parameters including impingement hole-to-hole pitch Pi, impingement hole diameter Di, impingement channel height H, and film hole diameter Df were selected to adjust within a reasonable range. The uniform design method was used to collect a database that represented the design space formed by the four parameters. Performance criteria including area-averaged overall cooling effectiveness, standard deviation of overall cooling effectiveness, and total pressure drop coefficient of the cooling system were evaluated through computational fluid dynamics (CFD) calculations. To explore and exploit the design space, a Kriging model was built from the database. Analysis of variance (ANOVA) was conducted afterward to investigate the main effect of each parameter and the correlation between parameters. Finally, based upon the knowledge obtained from ANOVA, typical designs were selected which yielded either best or poorest performances. Through detailed analysis of flow and heat transfer mechanisms of these designs, the influence of each parameter was illustrated clearly and suggestions for the design of similar cooling schemes were drawn.

Effects of Jet Impingement on Convective Heat Transfer in Effusion Holes

Abstract A common design for cooling the combustor liner of gas turbines is a double wall composed of impingement jets that feed effusion cooling holes. An important cooling mechanism associated with the effusion hole is the convective cooling provided to the liner wall, which is in contact with the hot main gas flowing through the combustor. While the combination of impingement jets and effusion holes has been studied earlier, mostly in terms of cooling effectiveness, investigators have not fully evaluated the effect the impingement jet has on the local internal convection within the effusion hole. This study evaluates the detailed effects of the impingement geometry on the local convective heat transfer coefficients within the effusion hole, which provides insights as to the design decisions for cooling combustor liners. Using a scaled-up, 3D-printed effusion hole with a constant heat flux boundary condition, local convective heat transfer coefficients were measured for a range of impingement geometries and positions relative to the effusion holes. Results showed a strong influence on the convective heat transfer resulting from the placement of the impingement hole relative to the effusion hole. In particular, the results showed a strong sensitivity to the circumferential and radial placement of the impingement jet with little sensitivity to the jet-to-effusion distance.

Experimental Investigation of Innovative Cooling Schemes on an Additively Manufactured Engine Scale Turbine Nozzle Guide Vane

Abstract This study includes the design, validation, and fabrication via direct metal laser sintering (DMLS) of a gas turbine nozzle guide vanes (NGV) that incorporates three innovative cooling schemes specifically enabled by additive manufacturing. The novel NGV design is the culmination of an extensive research and development effort over a period of 4 years that included low- and high-speed cascade testing coupled with unsteady computational fluid dynamics for numerous candidate innovative cooling architectures. The final vane design (SJ-vane) consists of sweeping jet (SJ) film cooling holes on the suction surface (SS), sweeping jet impingement holes at the leading edge and double-wall partial length triangular pin-fin with impinging jet at the trailing edge. For comparison purposes, a second DMLS enabled vane (777-vane) was designed and fabricated with prototypical cooling circuits to serve as a baseline. This vane consists of a shaped film cooling holes on the suction surface, circular impingement holes at the leading edge, and full-length cylindrical pin-fins at the trailing edge. Experiments with the two DMLS enabled vanes were performed at the Ohio State University Turbine Reacting Flow Rig (TuRFR) at engine-relevant temperature (1375 K) and Mach number conditions. Infrared (IR) thermography was utilized to measure the wall temperature of the pressure and suction surface at several coolant mass flowrates to estimate the overall cooling effectiveness (ϕ). Results showed improved cooling performance for the advanced cooling schemes (sweeping jet film cooling, impingement cooling, and triangular pin-fin cooling) compared with the baseline cooling schemes.

Parametric Studies of Laminated Cooling Configurations: Overall Cooling Effectiveness

Combing the advantages of film cooling, impingement cooling, and enhanced cooling by pin fins, laminated cooling is attracting more and more attention. This study investigates the effects of geometric and thermodynamic parameters on overall cooling effectiveness of laminated configuration, and model experiments were carried out to validate the numerical results. It is found that the increases in film cooling hole diameter and pin fin diameter both result in the increase in cooling effectiveness, but the increases in impingement hole diameter, impingement height, and spanwise hole pitch degrade the cooling performance. The increase of the coolant flow rate causes the increase in cooling efficiency, but this effect becomes weaker at a high coolant flow rate. The coolant-to-mainstream density ratio has no obvious effect on cooling effectiveness but affects wall temperature obviously. Moreover, based on the numerical results, an empirical correlation is developed to predict the overall cooling efficiency in a specific range, and a genetic algorithm is applied to determine the empirical parameters. Compared with the numerical results, the mean prediction error (relative value) of the correlation can reach 8.3%.

Experimental Study of Heat Transfer on the Internal Surfaces of a Double-Wall Structure with Pin Fin Array

The double-wall structure is one of the most effective cooling techniques used in many engineering applications, such as turbine vane/blade, heat exchangers, etc. Heat transfer on the internal surfaces of a double-wall structure was studied at impinging Reynolds numbers ranging from 1 × 104 to 6 × 104 using the transient thermochromic liquid crystal (TLC) technique. The two-dimensional distributions of Nusselt numbers and their averaged values were obtained on the impingement surface, target surface and the pin fin surface. The Nusselt number correlations on the surfaces mentioned above were determined as a function of Reynolds number. The results show that the second peak values of the Nusselt number distribution appear on the target surface at all Reynolds numbers studied in this paper for a short distance of the target surface to impingement surface. This phenomenon becomes significant with the further increase of the Reynolds number. The difference between the Nusselt number at the second peak and the stagnation point decreases with the increasing Reynolds number. The maximal Nusselt number regions on the impingement surface appear at the left and right sides of the pin fins between the two impingement holes. The Nusselt numbers of the pin fin surfaces are highly dependent on their various locations in the double-wall structures. The contributions of the impingement surface, pin fin surface and target surface to the overall heat transfer rate are analyzed. The target surface contributed the largest amount of heat transfer rate with a value of about 62%. The heat transfer contribution is from 18% to 21% for the impingement surface and 16% to 18% for the pin fin surfaces within the studied Reynolds numbers.

A high temperature turbine blade heat transfer multilevel design platform

In this work, a fast and efficiently design method has been introduced. This design process consists of the overall design and the detailed design. For the overall design, one-dimensional pipe-network computations are employed to obtain several design cases quickly at the beginning. Meanwhile the solid domain geometry and mesh with cooling structures, i.e., film holes, impingement holes, and ribs have been generated to carry out three-dimensional (3-D) heat conduction calculations. Based on the above, a detailed design has been performed by 3-D conjugate heat transfer calculations. The results show that both the average temperature and the mass flow maximum errors between the pipe-network and 3-D conjugate heat transfer calculations are about 10%. In this article, the cooling structure of a gas turbine blade is designed with this platform. The final design results show that the maximum dimensionless temperature on the blade surface is 0.813, i.e., lower than the design requirement. The dimensionless mass flow rate in the first cooling inlet is 0.0168, and the mass flow rate in the secondary inlet is 0.0231.

Numerical simulation of broken pin effects on the flow field and cooling performance of a double-wall cooling configuration

In this paper, the flow characteristics of the double wall structure are presented and the effect of the broken pin size on the cooling performance and flow field of the double wall configuration is investigated. A periodic plate model with seven units is adopted, and there are an impingement hole and a film hole in each unit. Under five blowing ratios, six different sizes of the broken pin are compared, and the double wall configuration without broken pins is taken as the baseline. The results show that if the broken pins height is too small, the cooling effectiveness usually cannot be improved. With the presence of broken pins with a height of more than 0.4, the effectiveness is improved due to the enhancement of reattachment and recirculation of coolant. With the increase of the broken pin height, the cooling effectiveness increases. However, the increase of the diameter does not always improve the cooling performance, since the limiting effect of the wall jet. In this study, Case 6 with the largest broken pin always has the best cooling performance, but also the largest flow resistance. In Case 6 temperature is reduced by almost 15 K compared to the baseline, and more areas have relatively higher cooling effectiveness.

Experimental and Computational Methods for the Evaluation of Double-Wall, Effusion Cooling Systems

Abstract Further improvements in gas turbine efficiency can be sought through more advanced cooling systems—such as the double-wall, effusion system—which provide high cooling effectiveness with low coolant utilization. The double-wall system, as described here, comprises two walls: one with a regular array of impingement holes and the other with a closely packed, regular array of film holes (characteristic of effusion systems). These walls are mechanically and thermally connected via a bank of pedestals which increase coolant wetted area and turbulent flow features. However, a lack of data exists in the open literature on these systems. This study presents a novel experimental heat transfer facility designed with the intent of investigating flat plate versions of such double-wall geometries. Key features of the facility are presented including the use of recirculation to increase the mainstream-to-coolant temperature ratio and the use of infrared thermography to obtain thermal measurements. Some rig commissioning characteristics are also provided which demonstrate well-conditioned, uniform flow. Both coolant and mainstream Reynolds numbers are matched to engine conditions, with the Biot number within around 15% of engine conditions. The facility is used to assess the cooling performance of four double-wall effusion geometries which incorporate various geometrical features. Both overall effectiveness and film effectiveness measurements are presented at a range of coolant mass flows with conclusions drawn as to preferable features from a cooling perspective. The results from a fully conjugate computational fluid dynamics (CFD) model of the facility are presented which utilized boundary conditions obtained during experimental runs. Additionally, a computationally efficient decoupled conjugate method developed previously by the authors was adapted to assess the experimental geometries with the results comparing favorably.

Experimental and numerical study on the flame characteristics and cooling effectiveness of air-cooled flame holder

For high-performance combustion, it needs to meet the requirements of flame stability and heat protection at a wide operating range. In this work, a novel air-cooled flame holding device containing impingement holes and faced film holes, which can achieve flame stabilization and reduce wall temperature. The cooling air flows out and forms vortices attaching on the back wall, functioning as a thickened film that reduces heat transfer and control the distance between the flame and the back wall. The novel composite cooling scheme worked effectively at reaction state and achieved an almost 20% reduction of wall temperature, and the cooling effect of the 30-deg faced film hole was much better than that of the 60-deg faced film hole. Flame stabilization was influenced by the increasing mass rate of cooling air. The oversize distance of flame stabilizing zone and back wall easily caused flame instability even blow-off. 0.3% and 0.5% mass rate of cooling air were enough to achieve flame stabilization and work effectively to decrease wall temperature. The novel air-cooled flame holder saw both flame stability and cooling effectiveness. Because of its compact design and resistance to thermal ablation, it can be of great importance for an advanced burner.