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Measurements in a 1.5 Mw Pressurized Gas Turbine Combustor Operated on Biomass Derived Low Calorific Fuel
Published in Naim Hamdia Afgan, Maria da Graça Carvalho, New and Renewable Energy Technologies for Sustainable Development, 2020
M. van der Wel, B. Adouane, Ö. Ünal, W. de Jong, H. Spliethoff
This combustor had been designed within the scope of a JOULE project (JOU2-CT92-0154). Figure 2 shows a cross section of the inlets of the TUD burner. To avoid the danger of flashback, the fuel gas and combustion air are admitted separately into the combustor. The air supply to the combustor is subdivided into two flows: primary combustion air and secondary air (film cooling). Primary air enters the combustor at the centreline through 24 holes with a diameter of 4 mm at an angle of 45° with the centreline. The main part (95%) of the fuel gas enters the combustor axially through an annular space at the end of the flame holder. The remaining part of the fuel gas enters the combustor through 24 holes, with a diameter of 5 mm at an angle of 22.5° with the centreline, in the flame holder. This ensures stable ignition of the main fuel gas flow. The flow pattern created by this burner is relatively simple because the entire combustion system is axi-symmetric and no swirl is generated in the fuel or airflow. Due to the conical shape of the flame holder and the directions of the inlet velocities of the primary combustion air and LCV fuel gas flows, a strong internal recirculation zone is created, which ensures thorough mixing of fuel and oxidant and back mixing of the hot combustion gases and stabilizes the flame.
Optical Deflectometry by Speckle Photography
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
The speckle measurements provide an analysis of the turbulent scalar field-density or temperature—independent of knowledge about the turbulent velocity field. A fundamental question is whether the density behaves like a passive scalar, i.e., whether the dynamics of turbulence are independent of the density (or temperature) fluctuations. This problem depends on the amplitude of the scalar fluctuations, and it is of great importance for modeling turbulent combustion processes. Applying the optical speckle technique, Oberste-Lehn and Merzkirch [28] showed that the scalar is passive even at RMS values of the temperature fluctuations of more than 30 K, which is about one third of the values experienced in technical flames. Experimentally determined energy spectra were compared with predictions of the “extended von Karman scalar model” [31], which is based on the assumption of a passive scalar, and showed reasonable agreement (Fig. 11). In these experiments, a turbulent temperature field was generated in the gas flow downstream of a turbulence grid by passing the flow through a plane combustion front at the grid that served as a flame holder. With the arrangement shown in Fig. 1, the application of the speckle technique is practically independent of the amplitude of the density changes or fluctuations.
Flow Visualization By Direct Injection
Published in Richard J. Goldstein, Fluid Mechanics Measurements, 2017
Thomas J. Mueller, F. N. M. Brown
Figure. 6.24 shows the supersonic flow past a wedge. This photograph was made using a modified schlieren system to be able to obtain simultaneous schlieren and smoke lines [38]. This photograph shows the two fundamental ways in which supersonic flow tends to follow parallel surfaces: flow through a shock wave and expansion around a corner. In the flow through the shock wave, the abrupt deflection of the streamline to flow parallel to the front surface of the wedge can be observed. The expansion at the shoulder of the wedge to follow parallel to the main body of the wedge is clearly seen. The Mach number (Ma) of the flow can be determined from the photograph by measuring the shock angle and the streamline deflection. In a similar way, streamlines can be followed throughout the flow field, and so map the entire flow field. To study wake flows, a lucite wedge-shaped plug with a rounded leading edge was inserted slightly upstream of the nozzle throat [61]. This configuration resembles a plug nozzle, referred to as the expansion-deflection nozzle, or may be thought of as representing a strut, a flame holder, a Scramjet fuel injector, etc.
Analysis of the Evolution of the Surface Density Function During Premixed V-Shaped Flame–Wall Interaction in a Turbulent Channel Flow at Reτ = 395
Published in Combustion Science and Technology, 2022
Reo Kai, Abhishek Lakshman Pillai, Umair Ahmed, Nilanjan Chakraborty, Ryoichi Kurose
Figure 1b shows the computational domain and conditions for the DNS of V-flame. The domain consists of two (flame and buffer) regions. The last 160 mm of the reacting simulation domain is kept as a buffer region so that the outflow boundary does not affect the reacting flow simulation, following previous analyses (Ahmed et al. 2019, 2020; Kitano et al. 2015). For the current analysis, the ratio of the friction velocity and the unstretched laminar burning velocity is (where is the unstretched laminar burning velocity). Thus, no flashback is expected because is not conducive to flashback in the case of hydrocarbon flames (Ahmed, Chakraborty, and Klein 2021b; Alshaalan and Rutland 1998, 2002; Gruber et al. 2010). The flame holder is placed in a fully developed wall-bounded turbulent flow to stabilize the flame and preclude any possibility of a flame blowout. It has been shown in previous studies (Ahmed, Chakraborty, and Klein 2021b; Alshaalan and Rutland 1998, 2002; Gruber et al. 2010) that a flame blowout is not expected in this configuration.
Modelling of Sub-Grid Scale Reaction Rate Based on a Novel Series Model: Application to a Premixed Bluff-Body Stabilised Flame
Published in Combustion Science and Technology, 2019
Weilin Zeng, Konstantina Vogiatzaki, Salvador Navarro-Martinez, Kai Hong Luo
In this part, results are presented for the series model in 2 mm resolution grids. Figure 2 shows typical vortical structures after the bluff-body, represented by iso-surfaces of vorticity magnitude. The large-scale coherent vortices are shed from the shear layer due to Kelvin-Helmholtz instabilities, which break down into smaller scale eddies downstream. A von Karman vortex street is established in the wake of the body characterised by nearly symmetric vortex shedding. Observing the temperature distribution in Figure 3, hot combustion products inside the recirculation zone incessantly mix with the cold co-flowing mixture, and sequentially ignition occurs in the shear/mixing layers. The ignited flame convects downstream and continues to ignite the neighbouring mixtures by heat transfer. The recirculation region behind the flame-holder, sustaining this continuous re-ignition process, stabilises the flame. The series model correctly reproduces the flame-anchoring features.