Gas Swirl Research Articles

Effects of the jet pulsation intensity on flame behavior, thermal structure and combustion product concentration of a gas turbine model with swirl combustor

Effects of jet pulsation intensity on flame behavior, thermal structure and combustion products concentration in a swirling dual-disk double-concentric jets are experimentally investigated at different swirling strengths, central fuel jet Reynolds number and excitation Strouhal number. Close-up and full length images of the flames were captured for different flame modes by a digital camera. A hot-wire anemometer was used for measuring the central jet velocities at different jet pulsation intensities. The flame temperatures were measured by a fine-wire thermocouple, at radial and axial directions. The toxic combustion products of different flame modes were measured with a gas analyzer. The flame lifted from blockage disk and stabilized over the control disk at large values of the jet pulsation intensity. The lifted flame was very turbulent, blue, short and stable. Low values of toxic combustion products NO, CO and UHCs were observed from the lifted flame. The lifted flame also had high temperatures at radial and axial direction. High values of the jet pulsation intensity can significantly improve combustion efficiency at flames of swirling dual-disk double-concentric jets. The acoustic excitation can significantly improve combustion efficiency at gas turbine and swirl combustors. As the swirl combustors are widely used at propulsion and power, efficiency of energy transmission systems can significantly improve at high jet pulsation intensities.

An Advanced Single-Stage Turbine Facility for Investigating Nonaxisymmetric Contoured Endwalls in the Presence of Purge Flow

AbstractIn modern gas turbines, endwall contouring (EWC) is employed to modify the static pressure field downstream of the vanes and minimize the growth of secondary flow structures developed in the blade passage. Purge flow (or egress) from the upstream rim-seal interferes with the mainstream flow, adding to the loss generated in the rotor. Despite this, EWC is typically designed without consideration of mainstream–egress interactions. The performance gains offered by EWC can be reduced, or in the limit eliminated, when purge air is considered. In addition, EWC can result in a reduction in sealing effectiveness across the rim seal. Consequently, industry is pursuing a combined design approach that encompasses the rim-seal, seal-clearance profile, and EWC on the rotor endwall. This paper presents the design of and preliminary results from a new single-stage axial turbine facility developed to investigate the fundamental fluid dynamics of egress–mainstream flow interactions. To the authors' knowledge, this is the only test facility in the world capable of investigating the interaction effects between cavity flows, rim seals, and EWC. The design of optical measurement capabilities for future studies, employing volumetric velocimetry (VV) and planar laser-induced fluorescence (PLIF), is also presented. The fluid-dynamically scaled rig operates at benign pressures and temperatures suited to these techniques and is modular. The facility enables expedient interchange of EWC (integrated into the rotor bling), blade-fillet and rim-seal geometries. The measurements presented in this paper include: gas concentration effectiveness and swirl measurements on the stator wall and in the wheel-space core; pressure distributions around the nozzle guide vanes (NGV) at three different spanwise locations; pitchwise static pressure distributions downstream of the NGV at four axial locations on the stator platform.

Influence of gas dynamics on arc dynamics and the discharge power of a rotating gliding arc

This work reports the design and characterization of a rotating gliding arc (RGA) reactor developed with novel electrode configuration. This RGA uses gas swirl discs having ‘tangential gas entry ports/holes’ (NH) to achieve arc rotation and does not employ any external magnets. This work investigates the effect of gas dynamics on (1) arc dynamics such as the arc’s rotation and shape; (2) voltage fluctuation pattern; and (3) plasma discharge power for the designed RGA. Experiments were conducted using argon as the plasma forming gas with (a) two gas swirl discs (NH = 3 and 12) and (b) three different gas flow rates (Q = 5, 25 and 50 LPM) as control parameters. Cold flow simulation (CFS) studies using a multidimensional solver were used to understand gas dynamics. The arc rotational frequency (farc) measured from (1) a high-speed camera (HSC) and (2) fast Fourier transform (FFT) analysis of voltage, shows linear dependency on the Reynolds number (Re) calculated from CFS, with an R2 = 0.98. The agreement improves (R2 = 0.99) by applying linear fit only for the cases having turbulent Re. A close match between gas rotational frequency (fgas) calculated from CFS and experimentally measured farc is seen. The turbulent regime of the gas flow causes: (1) twisting and bending of the arc; (2) sawtooth-like voltage fluctuations with irregular and non-sinusoidal waveform; and (3) arc blow off. The high-frequency voltage fluctuations were reduced/absent when the flow Re reduced from ≈6.0 × 104 to ≈1.0 × 104. These findings establish that the gas dynamics, in particular, the bulk flow phenomenon of the gas, has an explicit influence on arc dynamics of the RGA reactor. This novel RGA design has the potential to replace magnetically driven rotating gliding arc systems.

Synchrotron radiography characterization of the liquid core dynamics in a canonical two-fluid coaxial atomizer

The liquid core of a canonical two-fluid coaxial atomizer has been characterized using synchrotron X-rays. The high energy photons allow for high-speed imaging of attenuation through the dense liquid-gas jet core, resolving the internal structures that include entrapped air bubbles and the formation of liquid ligaments and bags. When the gas-to-liquid momentum ratio increases, the liquid core transitions from an intact column, where primary break-up happens several liquid diameters downstream, to a hollow crown with a downstream span comparable to the liquid diameter that disintegrates by shedding ligaments from its rim. At high gas momentum ratios (limited by the sonic velocity at the gas nozzle exit), this crown suffers partial dewetting and, when angular momentum is added to the gas, it dewets on a large section of the liquid injection needle circumference. This partial crown exhibits azimuthal motions along the circumference, on timescales much longer than the relevant flow timescales. The crown attachment to the liquid needle presents a bi-stable nature. The dramatic changes of the liquid core morphology, as the gas momentum and swirl ratios vary, have a strong impact on the gas-liquid boundary layers, which control the liquid break-up mechanisms and the resulting spray characteristics, such as droplet size distributions and the droplet volume fraction across the spray.

Large Eddy Simulation of a dual swirl gas turbine combustor: Flame/flow structures and stabilisation under thermoacoustically stable and unstable conditions

A laboratory gas turbine model combustor with dual-swirler configuration is investigated using Large Eddy Simulation (LES) with a flamelet subgrid combustion model. Two partially premixed methane/air flames with different equivalence ratio and thermal power are simulated: one stably burning with an elongated V-shape and another undergoing pronounced thermoacoustic oscillations exhibiting a flat shape. Additionally, both flames feature a hydrodynamic instability in the form of a precessing vortex core (PVC). Detailed comparisons between experimental and LES results show that the different flow and reaction zone structures in these two flames are reproduced well. The various flow dynamics resulting from the PVC and thermoacoustic oscillations are also captured accurately in the simulation. Further analyses on the lifted swirl flame stabilisation using phase averaged statistics at the PVC frequencies reveal that the PVC-induced stagnation points provide an anchoring mechanism for both the stable and unstable flames, although in the latter case large self-excited pressure oscillations are present. It is found that the PVC is significantly influenced by these oscillations, being axially stretched and compressed at high and low pressures, respectively. However, the formation of flame leading edge due to the PVC is robust during these unstable processes and the azimuthal movement of the leading point is found to be strongly correlated with the rotation of the PVC in both flames, further confirming the vital role of the PVC in the stabilisation process of these lifted swirl flames.

Linear and Non-linear Analysis of Breakup of Liquid Sheets: a Review

Atomization primarily involves interaction between liquid and surrounding gaseous medium resulting in the growth of unstable waves on a distorted liquid surface. There is a huge volume of work surrounding various models and theories involved in investigation of interface dynamics during sheet breakup. The present work summarizes the linear and nonlinear studies for different geometrical shapes of liquid sheet such as planar, annular, and swirling. The techniques involved in deriving nonlinear governing equations such as perturbation technique, multiple scales approach, and long wave approximation have been outlined. Effects of various factors on sheet instability such as viscosity, compressibility, surface temperature difference, unequal velocity, lateral waves and gas swirl have been listed. Research lacunae and scope of future work are presented in the summary.

Effect of hydrogen addition on combustion and emission characteristics of methane fuelled upward swirl can combustor

The present research aims to assess the potential of hydrogen in the form of a supplementary fuel to accelerate combustion chemistry and reduce CO emissions of methane fuelled upward swirl gas turbine combustor. Effects of hydrogen enrichment on flame characteristics and chemical kinetics are analysed using Large Eddy Simulations (LES). Flame visualization is performed and measurements of temperature and emissions at the exit of combustor are reported. For the same energy input, flames are relatively broader and shorter at higher hydrogen concentrations. Augmentation of hydrogen is advantageous in terms of flame velocity, temperature, rate of chemical reactions and CO emissions. Higher flame temperature favours NOx emissions at higher hydrogen content. At a constant volumetric fuel flow, reduction in carbon-generated species is attributed to hydrocarbon substitution and chemical kinetic effects are less. Hydrogen addition increases flame temperature, decreases flame dimensions and reduces CO emissions with marginal increase in NOx emissions.

Comparison of studies on flow and flame structures in different swirl combustors

Swirling gas combustion and two-phase combustion (spray-air or particle-air combustion) are widely encountered in gas-turbine combustors and internal combustion engines. In experimental studies of practical combustors frequently it is difficult to get the detailed information inside the combustors. Most of numerical simulation is Reynolds-averaged (RANS) modeling, which cannot give detailed flow and flame structures. Some investigators reported their results using large-eddy simulation (LES) with different combustion models. The present authors did systematic LES studies on swirling gas combustion and two-phase combustion using second-order moment (SOM) and EBU combustion models. The statistic results are assessed by the measurement results. The instantaneous results show the flow and combustion behavior in different swirl combustors.

An experimental study on premixed CNG/H2/CO2 mixture flames

Abstract In this study, the effect of swirl number, gas composition and CO2 dilution on combustion and emission behaviour of CNG/H2/CO2 gas mixtures was experimentally investigated in a laboratory scale combustor. Irrespective of the gas composition, thermal power of the combustor was kept constant (5 kW). All experiments were conducted at or near stoichiometric and the local atmospheric conditions of the city of Kayseri, Turkey. During experiments, swirl number was varied and the combustion performance of this combustor was analysed by means of centreline temperature distributions. On the other hand, emission behaviour was examined with respect to emitted CO, CO2 and NOx levels. Dynamic flame behaviour was also evaluated by analysing instantaneous flame images. Results of this study revealed the great impact of swirl number and gas composition on combustion and emission behaviour of studied flames.

High effective heterogeneous plasma vortex reactor for production of heat energy and hydrogen

This work is a continuation of our previous studies [1-10] of physical parameters and properties of a long-lived heterogeneous plasmoid (plasma formation with erosive nanoclusters) created by combined discharge in a high-speed swirl flow. Here interaction of metal nanoclusters with hydrogen atoms is studied in a plasma vortex reactor (PVR) with argon-water steam mixture. Metal nanoclusters were created by nickel cathode’s erosion at combined discharge on. Dissociated hydrogen atoms and ions were obtained in water steam by electric discharge. These hydrogen atoms and ions interacted with metal nanoclusters, which resulted in the creation of a stable plasmoid in a swirl gas flow. This plasmoid has been found to create intensive soft X-ray radiation. Plasma parameters of this plasmoid were measured by optical spectroscopy method. It has been obtained that there is a high non-equilibrium plasmoid: Te > TV >> TR. The measured coefficient of energy performance of this plasmoid is about COP = 2÷10. This extra power release in plasmoid is supposed to be connected with internal excited electrons. The obtained experimental results have proved our suggestion.

Hydrogen production by conversion of ethanol injected into a microwave plasma

Reforming of gaseous and liquid hydrocarbon compounds into hydrogen is of high interest. In this paper we present a microwave (2.45 GHz) plasma-based method for hydrogen production by conversion of ethanol (C2H5OH) in the thermal reforming process in nitrogen plasma. In contrast to our earlier investigations, in which C2H5OH vapour was supplied into the microwave plasma region either in the form of a swirl or axial flow, in this experiment we injected C2H5OH vapour directly into the nitrogen microwave plasma flame, behind the microwave plasma generation region. The experimental results were as follows. At an absorbed microwave power of 5 kW, N2 (plasma-generating gas) swirl flow rate of 2700 NL(N2)/h and C2H5OH mass flow rate of 2.7 kg(C2H5OH)/h the hydrogen production rate was 1016 NL(H2)/h, which corresponds to the energy yield of hydrogen production 203 NL(H2)/kWh. After the C2H5OH conversion the outlet gas contained 27.6% (vol.) H2, 10.2% CO, 0.2% CO2, 4.8% CH4, 4.3% C2H2, 3.7% C2H4 and 3.7% C2H6. These results are comparable to those obtained in our earlier investigations, in which different methods of C2H5OH vapour supply to the microwave plasma generation region were employed.Graphical abstract

Mass and heat transfer from the surface of a gas sparged pool of liquid to an immiscible liquid under swirl flow and potential applications

Rates of mass and heat transfer (by analogy) between a gas sparged mercury pool and a swirling aqueous solution were studied by the electrochemical technique. Variables studied were superficial gas velocity, physical properties of the solution, and swirl flow velocity. The data were correlated by the equation:Sh=0.011Sc0.33Reg0.31Ren0.23The overall mass transfer coefficient due to the combined gas sparging and swirl flow k can be calculated in terms of the individual gas sparging mass transfer coefficient kg and swirl flow mass transfer coefficient ks from the equation:k=[kg3+ks3]0.33Application of the present results in the recovery of heat from low melting point liquid metal pools [such as mercury, gallium, indium and tin] in the production stage by direct cooling with water or high boiling point liquids was pointed out. Implication of the present results for the rational design of high space–time yield batch recycle electrochemical reactor with a mercury pool cathode suitable for conducting diffusion controlled electroorganic synthesis was highlighted.Liquid–liquid extraction processes involving surface active organic solutes which form stable emulsions between the dispersed phase and the continuous phase can be benefited from the present results in the design of a high productivity extractor.

Swirling Gas Jet-Assisted Laser Trepanning for a Galvanometer-Scanned CO2 Laser

Laser-drilled hole arrays are part of an important field that aim to improve efficiency without affecting the quality of laser-drilled holes. In this paper, a swirling gas jet was implemented to assist with laser trepanning for a galvanometer scanned CO2 laser. The proposed swirling gas jet is based on laser trepanning. This swirling gas jet nozzle was composed of four inlet tubes to produce the flow of the vortex. Then, the plume particles were excluded, and spatter on the surface of the workpiece decreased. Thus, this approach can mitigate the problem of overcooling. This study manipulated the appropriate parameter settings, which were simulated by computational fluid dynamics software ANSYS CFX. The proposed swirling gas jet can be used with galvanometer-based scanner systems to keep the laser beam from interference by spatter. In addition, a hollow position of the vortex was achieved by using the four inlet tubes, which resulted in pressure asymmetry in the nozzle and velocity distribution on the surface of the workpiece. The experiment verified that the depth of processing could be enhanced by 110% when trepanning at a scanning speed of 30 mm/s, and that the removal of volume could be enhanced by 71% in trepanning at a diameter of 1 mm by using a swirl assistant compared with a non-assisted condition. Furthermore, the material removal rate of the swirling jet increases when the machining area of the galvanometer-based scanner is larger.

이중선회 가스터빈 모델연소기에서 맥놀이 현상으로 인한 연소불안정 특성

이중선회 가스터빈 모델연소기에서 맥놀이 현상으로 인한 연소불안정 특성

Understanding the effect of operating conditions on thermal stratification and heat release in a homogeneous charge compression ignition engine

Thermal stratification of the unburned charge prior to ignition plays a significant role in governing the heat release rates in a homogeneous charge compression ignition (HCCI) engine. A deep understanding of the conditions affecting thermal stratification is necessary for actively managing HCCI burn rates and expanding its operating range. To that end, a single-cylinder gasoline-fueled HCCI engine was used to characterize the relationship between key operating conditions, such as intake temperature, residual gas fraction, air-to-fuel ratio, and swirl, and thermal stratification. The recently developed Thermal Stratification Analysis was applied to calculate the unburned temperature distribution prior to ignition from heat release.A comparison between re-induction of exhaust gas with an air-to-fuel ratio of 24:1 and air dilution with an air-to-fuel ratio of 43:1 shows that the presence of internal residuals increases the burn duration by 34% and broadens the temperature distribution by as much as 15%. The results from an intake temperature and combustion phasing sweep at an air-to-fuel ratio of 20:1 show that heat release rates increase with advancing CA50 phasing; however, the temperature distributions broaden by 48% when comparing the most advanced to most retarded cases. To add further insight by removing the effect of combustion phasing, an equivalence ratio sweep is compared to an intake temperature sweep. It is shown that a significant part of the broadening of the distributions can be attributed exclusively to the increased intake temperature which elevates the maximum TDC temperature while leaving the wall region unaffected. However, combustion phasing plays a role as well, with earlier combustion phasing being responsible for an additional broadening of the temperature distribution.The addition of swirl elongates the burn duration by broadening the temperature distribution, with this effect being slightly larger at earlier combustion phasings. However, swirl significantly increases heat transfer losses and reduces efficiencies by as much as 1.8 percentage points. Finally, a load sweep with compensation to ensure constant combustion phasing indicates that higher loads result in increased heat release rates and narrower temperature distributions by as much as 20%.

Numerical and experimental investigation of surface vortex formation in coolant reservoirs of reactor safety systems

Abstract The reliable operation of the emergency coolant pumps and passive gravitational injection systems are an important safety issue during accident scenarios with coolant loss in pressurized water reactors. Because of the pressure drop and flow disturbances surface vortices develops at the pump intakes if the water level decreasing below a critical value. The induced swirling flow and gas entrainment lead to flow limitation and to pump failures and damages. The prediction of the critical submergence to avoid surface vortex building is difficult because it depends on many geometrical and fluid dynamical parameters. An alternative and new method has been developed for the investigation of surface vortices. The method based on the combination of CFD results with the analytical vortex model of Burgers and Rott. For further investigation the small scale experiments from the Institute of Nuclear Techniques of the Budapest University of Technology and Economics are used which were inspired from flow limitation problems during the draining of the bubble condenser trays at a VVER type nuclear power plants.

Experimental and numerical analysis of natural bio and syngas swirl flames in a model gas turbine combustor

Turbulent reacting flows in a generic swirl gas turbine combustor model are investigated both numerically and experimentally. In the investigation, an emphasis is placed upon the external flue gas recirculation, which is a promising technology for increasing the efficiency of the carbon capture and storage process, which, however, can change the combustion behaviour significantly. A further emphasis is placed upon the investigation of alternative fuels such as biogas and syngas in comparison to the conventional natural gas. Flames are also investigated numerically using the open source CFD software OpenFOAM. In the numerical simulations, a laminar flamelet model based on mixture fraction and reaction progress variable is adopted. As turbulence model, the SST model is used within a URANS concept. Computational results are compared with the experimental data, where a fair agreement is observed.

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

연소실 길이에 따른 이중선회 가스터빈 모델 연소기에서 연소불안정 모드 연구

연소실 길이에 따른 이중선회 가스터빈 모델 연소기에서 연소불안정 모드 연구

Numerical Analysis of Turbulent Combustion in a Model Swirl Gas Turbine Combustor

Turbulent reacting flows in a generic swirl gas turbine combustor are investigated numerically. Turbulence is modelled by a URANS formulation in combination with the SST turbulence model, as the basic modelling approach. For comparison, URANS is applied also in combination with the RSM turbulence model to one of the investigated cases. For this case, LES is also used for turbulence modelling. For modelling turbulence-chemistry interaction, a laminar flamelet model is used, which is based on the mixture fraction and the reaction progress variable. This model is implemented in the open source CFD code OpenFOAM, which has been used as the basis for the present investigation. For validation purposes, predictions are compared with the measurements for a natural gas flame with external flue gas recirculation. A good agreement with the experimental data is observed. Subsequently, the numerical study is extended to syngas, for comparing its combustion behavior with that of natural gas. Here, the analysis is carried out for cases without external flue gas recirculation. The computational model is observed to provide a fair prediction of the experimental data and predict the increased flashback propensity of syngas.