Abstract

Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions. 

Abstract

This paper provides a CFD comparison of tow turbulence modeling approaches (SST) and (K-epsilon), with application to the simulation of a teardrop. As well as, the study investigates and compares among 3 different models in a range these types in order to assess the suitability of CFD for use when calculating drag co-efficient. Moreover, the study focuses on 3 different velocities to be impacted with the drag co-efficient. Whereas, the pressure over the body was used to calculate the drag co-efficient for each of the 3 teardrops shapes.

This paper presents the dynamic crushing performance of corrugated composite plate with different profiles. Samples of sinusoidal, square, and triangular corrugated profiles were experimentally tested. They were subjected to axial impact load. A weight of 10.5 kg have been freely dropped from a height of 1m, 2m, and 3m. The idea is to understand the effect of corrugation geometry on energy absorption performance. All specimens have been manufactured by hand lay-up technique using woven roving E-glass fabric and polyester resin with six layers. Similar specimens have been tested before under the effect of quasi-static compression load. Quasi–static testing is simpler and less expensive than dynamic testing and facilities are more readily available. Quasi–static can provide good qualitative assessment as to the trend of different variables upon energy absorption. However, for useful design data, dynamic testing is essential to determine a quantitative measure of energy absorption. Results obtained from dynamic tests conducted showed that corrugation profile has high effect on energy absorption capability. It is also observed that, specimens of square profile recorded the highest capability of energy absorption characteristics compared with sinusoidal and triangular profiles. This result came exactly in conformity with the results of quasi-static load applied on similar specimen that performed in a previous research.

The quality requirements for concrete reinforcement have increased interest in optimizing the mechanical properties of reinforcing bars used for the construction of all types of structures such as buildings, bridges and other constructions. The variability of mechanical properties of reinforcing steel bars manufactured from scrap metals by local manufacturers in Libya have been investigated in this paper. Sydee-Assayh Steel Factory (SASF) is one of the private steel factories established recently in Libya. This factory uses mainly scrap metals as raw material. This was motivated by the fact that it has been noticed that the use of the substandard reinforcing bars in construction industry could lead to collapse of the structures reinforced with these bars in many developing countries. Therefore a series of experimental tests were conducted to find mechanical properties of Sydee-Assyh Steel Factory products. Steel rods samples of 12mm and 14mm diameter were selected randomly and tested. Results found were compared with Libyan specifications (LNS-75) and ASTM standard (A-615), and found almost satisfactory.

Due to the increased rate of failure of wind generators, condition-monitoring system plays a significant role in overcoming failures resulting from the harsh operation conditions. The mathematical, thermal, and electrical analyses may be utilized to detect the faults of wind generators by monitoring the changes in their characteristics under different operation conditions. The behavior of the rotating permanent magnet of the generator can indicate the wind generator’s condition. For instance, the torque of the permanent magnet of the generator is affected by the oscillation of the magnet temperature. Therefore, monitoring the torque of the permanent magnet with respect to the rate of change in the permanent magnet temperature defines the generator health. Furthermore, the rate of change in the generator temperature is considered an additional indicator to define the health of the wind generators with respect to the induced electrical torque. That is because of the negative effect of the elevated generator temperature on the induced electrical torque. In this study, a different methodology has been adopted to implement a proper condition monitoring system on the wind generators by evaluating the rate of change in the generator temperature and permanent magnet temperature with respect to the induced electrical torque and the

.driving torque of the rotating permanent magnet under different operation conditions.

A case study, which is based upon collected data from actual measurements, is presented in this work in order to demonstrate the adequacy of the proposed model.

Assessment of airfoil aerodynamic characteristics is essential part of any optimal airfoil design procedure. This paper illustrates rapid and efficient method for determination of aerodynamic characteristics of an airfoil, which is based on viscous-inviscid interaction. Inviscid flow is solved by conformal mapping, while viscous effects are determined by solving integral boundary layer equations. Displacement thickness is iteratively added to the airfoil contour by alternating inviscid and viscous solutions. With this approach efficient method is developed for airfoil design by shape perturbations. The procedure is implemented in computer code, and calculation results are compared with results of XFOIL calculations and with experiment. Eppler E387 low Reynolds number airfoil and soft stall S8036 airfoil are used for verification of developed procedure for Reynolds numbers 200000, 350000, and 500000. Calculated drag polars are presented in this paper and good agreement with experiment is achieved as long as small separation is maintained. Calculated positions of laminar separation, reattachment, and turbulent separation closely follow experimental measurement. The calculations are performed in relatively short time, which makes this approach suitable for low Reynolds number airfoil design.

In order to examine the protection A postulated initiating event is explored step insertion of a positive reactivity in order to investigate the safety of the reactor of the Tajoura Nuclear Research Reactor with Low Enriched Uranium (LEU). These initiated events are:; a reduction of flow of primary coolant; and a loss of flow accident (LOFA) followed by a reversal flow. PARET computer code is implemented to simulate those suggested initiating events. The transient thermal hydraulic analysis is obtained at both the hottest and averaged cells of the core. The simulation is carried out at the operating power of 10 MW and the inlet coolant temperature equals to 45°C. The results exhibit that the worst case of those examined postulated events is by adding a 1.5$ ramp positive reactivity to the core when the resultant maximum clad surface temperature reaches 130.3°C.

Abstract

Swirl stabilized flows are the most widely deployed technology used to stabilize gas turbine combustion systems. However, there are some coherent structures that appear in these flows close to the nozzle whose occurrence and stability are still poorly understood during transition. The external recirculation zone and the Precessing Vortex Core to/from the Coanda effect are some of them. Thus, in this paper the transition of an Open Jet FlowMedium Swirl flow pattern to/from a Coanda jet flow is studied using various geometries at a fixed Swirl number. Phase Locked Stereo Particle Image Velocimetry and High Speed Photography experiments were conducted to determine fundamental characteristics of the phenomenon. It was observed that the coherent structures in the field experience a complete annihilation during transition, with no dependency between the structures formed in each of the flow states. Moreover, transition occurs at a particular normalized step size whilst some acoustic shifts in the frequencies of the system were noticed, a phenomenon related to the strength of the vortical structures and vortices convection. It is concluded that a transient, precessing, Coanda Vortex Breakdown is formed, changing flow dynamics. The structure progresses to a less coherent Trapped Vortex between the two states. During the phenomenon there are different interactions between structures such as the Central Recirculation Zone, the High Momentum Flow Region and the Precessing Vortex Core that were also documented.

For safety evaluation of the core of reactor at Tajoura Nuclear Research Centre (TNRC), a special case has been investigated when the power supply is cutoff and all primary circuit pumps are stopped and scram is occurred. In this case, the coolant flow through the core decreases from a forced convective flow to zero flow and at last becomes an upward flow due to natural circulation flow induced between the core and the reactor pool in which the core is submerged, hence, a core flow reversal occurs. This study focuses on the calculations of the safety parameters during the core cooling by natural convection via constructing a MATLAB program. The transient thermal hydraulic analysis was carried out for the hottest cell in the core. The simulation is performed when the operating power of the core equals to 10 MW and the operation time before scram equals to 72 hr. The results are obtained at the hottest channel for almost 6hr after scram and showed that the maximum clad surface temperature during cooling by pure natural convection decreases from 94.2°C to 60.9°C. The maximum clad surface temperature does not exceed the maximum allowable value of the clad surface temperature which is 102°C [1]. This study proves the capability of cooling the reactor core at TNRC after loss of off-site power.

Lean premixed swirl stabilised combustion is regarded as one of the most successful technologies for flame control and NOx reduction. The important characteristics of these flows are the good mixing, flame stability through the formation of a Central Recirculation Zone, and the low emissions at lean conditions as a consequence of temperature drop. Now the potential wide range of available fuels presents a problem in terms of variation of heating values, flame speeds and chemical reactivity. Process, refinery gases and gasified coal or biomass are just a few examples. The biggest challenge to fuel-flexibility of most combustors is the large differences between natural gas and the proposed replacement fuels which causes variations in the stability profiles of the combustion process. In this paper, lean premixed swirl combustion of CH 4 /H 2 /CO fuel mixtures was investigated experimentally and numerically to understand the impacts of these fuels on fundamental stability phenomena such as blowoff. The swirl burner used was operated at atmospheric pressure and ambient temperature using a moderate swirl number. Different nozzles were used to determine the impact of the blends on the Central Recirculation Zones. Methane content in the fuel was decreased from 50% to 0% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Chemical kinetic analyses were carried out using PRO-CHEMKIN to determine flame speeds and chemical properties needed for CFD calculations. Experiments were done using a Phase Locked PIV system. The Central Recirculation Zone and its turbulence were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the blend, with a shift of turbulence based on carbon-hydrogen ratio, nozzles effects on the shearing flow and Re numbers. Correlation with the phenomenon was also achieved using the k-cc SST CFD model, providing more information about the impact of the CRZ and the flame turbulent nature close to the blowoff limit.