Gaoen Liu

Measured Film Cooling Effectiveness of Three Multihole Patterns

As an advanced cooling scheme to meet increasingly stringent combustor cooling requirements, multihole film cooling has received considerable attention. Experimental data of this cooling scheme are limited in the open literature in terms of different hole patterns and blowing ratios. The heat-mass transfer analogy method was employed to measure adiabatic film cooling effectiveness of three multihole patterns. Three hole patterns differed in streamwise row spacing (S), spanwise hole pitch (P), and hole inclination angle (α), with the first pattern S/P=2 and α=30°, the second S/P=1 and a=30°, and the third SIP=2 and a =150°. Measurements were performed at different blow ratios (M=1-4). Streamwise coolant injection offers high cooling protection for downstream rows. Reverse coolant injection provides superior cooling protection for initial rows. The effect of blowing ratio on cooling effectiveness is small for streamwise injection but significant for reversion injection.

Investigation of Film Cooling Effectiveness of Full-Coverage Inclined Multihole Walls With Different Hole Arrangements

An experimental and numerical investigation of adiabatic film cooling effectiveness was conducted on four full-coverage inclined multihole walls with different hole arrangements. The hole geometrical patterns and the test conditions were chosen to be representative of film cooling designs for modern aeroengine combustor liners. The four hole arrangements were grouped into two types based on lateral hole pitch ( P ) and streamwise row spacing ( S ). One type included two test plates which had the same S and P (S/P = 2) and compound angle (β = 0 deg) but different hole inclination angles ( α ) (30 and 150 deg ). The other type included two test plates which had the same S and P (but S/P = 1) and inclination angle (α = 30 deg) but different compound angles (0 deg and 50 deg). Heat-mass transfer analogy method was employed to investigate the adiabatic film cooling effectiveness of these multihole walls with typical blowing ratios for aeroengine combustors. The numerical simulation was performed to characterize the flowfield and temperature distribution, aiming to further understand the film cooling mechanisms. The experimental results indicated that blowing ratio within the range from 1 to 4 had negligible influence on adiabatic film cooling effectiveness (η) in the case of concurrent coolant injection while hole arrangement had large effect on η. But the blowing ratio within the range from 1 to 4 had large effect on the film cooling effectiveness for the counterflow film cooling scheme. The numerical results were compared with experimental data and fairly good agreement was obtained. The numerical simulation revealed the flow structure, particularly exhibiting significant influence of the interaction between mainstream flow and coolant jets on η. With validation by experimental data, film cooling numerical simulation seems quite helpful in selecting optimum multihole arrangement for modern combustor liner design.Copyright

Effect of Impingement/Effusion Hole-Area Ratio on Discharge Coefficients of Double Cooling Wall

This paper presents the experimental investigations on the discharge coefficients of impingement/effusion double flat wall with the impingement/effusion hole-area ratios of 1, 0.64 and 0.28. The impingement and effusion walls researched have equal numbers of holes per unit surface area in diamond arrays. The impingement holes are normal to the wall surface, the effusion holes are 30 degree to the wall surface in the sreamwise direction of the main flow, and both the impingement and effusion holes are arranged in the staggered mode. The CFD code was also applied to investigate the flow field within the impingement/effusion wall in detail. The experimental results indicated the relationship of the discharge coefficients of the single impingement wall, effusion wall and double wall with the overall pressure parameter of double wall in different impingement/effusion hole-area ratios, and were explained in the CFD results.Copyright

LBO Performance Comparison Between Two Combustors With Different Swirl Cups

Lean Blowout (LBO) performance is very important to the aero and ground gas turbine combustors. A typical liquid-fueled gas turbine combustor is the one with swirl cup dome which plays an important role to the LBO. The swirl cup dome comprises swirlers and nozzle usually. The swirlers serve to generate a toroidal flow reversal that entrains and recirculates a portion of the hot combustion products to mix with the incoming fresh air and fuel, so it makes the recirculation region the sustainable source of ignition. Swirlers in present study generally are two or three stages, and the nozzle takes different atomization styles, such as pressure-swirl atomization, prefilming and airblast atomization. Different swirlers matching various nozzles form all kinds of swirl cup domes, and each swirl cup dome of combustor would have different LBO performance and other combustion properties resulting from its structure characteristics. The flow flux arrangement and spray distribution are the two important factors to determine the combustor performance. Two combustor dome test rigs were investigated, of which one comprises with three air swirlers and a fuel prefilming nozzle (dome A), and the other is composed of two air swirlers and a fuel pressure nozzle (dome B). Tests were conducted to get the LBO fuel air ratio at atmospheric pressure. To explain the experimental results, numerical simulations were performed for cool flow fields of two combustors, also the cold flow field and spray of the two combustors’ dome downstream were measured by PDA with water instead of kerosine. The flame pictures near LBO were taken. The preliminary results indicated that the combustor with dome A had better spray uniformity than the one with dome B, but it had a little worse LBO performance. The air flow mass percentage of the inner swirler of dome A should decrease to some extent in order to establish a lower pressure region at the outlet of dome A, which would be helpful to decrease the LBO fuel air ratio and so as to improve the LBO performance. The two domes had their own advantages, and if the benefits of both were integrated, it was possible to design a better swirl cup dome.Copyright

Investigation of Tangential Trapped Vortex Combustor

An innovative concept of Tangential Trapped Vortex Combustor (TTVC) applying a swirling flow to eliminate the guide vanes of the compressor and turbine in the future gas turbine engines is presented via theoretical analysis and experimental investigation. In TTVC, the airflow is mostly whirlblast, and the processes of evaporation, mixing, and chemical reaction for the liquid spray combustion take place along the tangential direction. It is shown that the TTVC operation has the potential of improving combustion efficiency, widening combustion stability range, and reducing emissions, mainly due to the effects of trapped vortex, high centrifugal force, and periodical mixing. Experimental results of the ignition and LBO limits in a small 4-cup annular TTVC operating at atmospheric pressure demonstrated that this innovative combustion technology has a good LBO limit performance to meet the requirements of advanced gas turbine engines.Copyright

Flow Field and Heat Transfer Characteristics in an Impingement/Effusion Cooling System for Combustor Liner

The present study is conducted to investigate the characteristics of the flow field and heat transfer in an impingement/effusion cooling scheme for gas turbine combustor liner. It is designed to provide an insight, through the study of the flow field, into the physical mechanisms responsible for the enhanced impingement heat transfer near the effusion hole entrance. In this impingement/effusion cooling scheme, the angle between the impingement hole and effusion hole and the wall surface are 90 deg and 30 deg respectively. The square arrays of impingement/effusion holes are used with equal numbers of holes offset half a pitch relative to each plate so that an impingement jet is located on the center of each four effusion holes and vice versa. The flow field of the double skin wall space is described by the way of Particle Image Velocimetry (PIV). Two kinds of target plates, with and without effusion holes, are used in the impingement heat transfer study. Through changing the impingement Reynolds and the impingement gap, the change of the impingement heat transfer coefficient on the target plates is investigated. The impingement heat transfer test results show that the impingement heat transfer is enhanced near the entrance of the effusion holes, which could fully explain the feature of the impingement heat transfer coefficient on the target plate.Copyright

Investigation of Combustion Performance of a Hybrid Airblast Atomizer Under Simulated Low Power Conditions

An aero gas turbine combustor has to meet requirements for both high and low power condition operation. Within the requirements for low power conditions, lean-blow-out (LBO) and combustion efficiency are the basic ones. A pure prefilming air blast atomizer may have difficulty meeting combustion requirements under low power conditions, such as, idle LBO, idle combustion efficiency, etc. Use of a hybrid airblast atomizer may offer a solution for such problems. A hybrid airblast atomizer is a single fuel injection unit that has both pilot and main fuel circuits. A simplex nozzle is often used for pilot fuel circuit and an airblast atomizer of the swirl cup type may be used for the main fuel circuit. For the main fuel circuit, fuel is injected from a number of plain jet holes. The fuel jets are injected towards a venturi, with the help of swirling air from another air swirler, and the main fuel is airblasted and well mixed with both swirler airflows. For low power conditions, the pilot fuel nozzle (simplex nozzle) works alone. Not all of the swirler air will mix with pilot nozzle fuel spray. With appropriate pilot nozzle pressure drop and with some airblast function, the pilot fuel is well atomized and does not fully mix with the swirler air nor with primary hole air. Thus, the low power condition combustion efficiency is improved. The investigation reported in the present paper has concentrated on hybrid atomizer combustion performance under simulated low power conditions, when only the pilot nozzle is operating. The study consists of the following parts: • Pilot nozzle drop size measurement; • Numerical simulation of combustor flow field; • Atmospheric ignition test; • Simulated idle condition LBO test; • Low power condition combustion efficiency test. Results are reported, and future work is defined.Copyright