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Show In this work an attempt has been made to experimentally investigate the combustion process and flame stabilization in a single spherical dimple, that is a vortex generator, located on the streamlined surface. Particular attention has been given to identify regimes of insensitive flame stabilization in the dimple as well as to evaluate the possibility of using the vortex generators to establish natural gas combustion and to enhance heat transfer in a gas-fired equipment. EXPERIMENTAL EQUIPMENT AND PROCEDURE An experimental investigation of flow pattern and heat transfer in a dimple has been performed in a subsonic wind tunnel. Experiments on investigation of free stream turbulence effect on flow pattern and heat transfer in the dimple were pursued in the same wind tunnel with a rectangular cross section of 200mmx400mm. The hemispherical dimple with diameter d= 150mm was set in the middle of the wider wall of the tunnel. The average flow velocity in the tunnel comprised was tV0=33.6 m/sec; the root-mean-square values of free stream longitudinal velocity component fluctuations were <U' 2>°'5/U0 = 0.005; the boundary layer thickness upstream the dimple was 15 m m , and the flow temperature comprised 7o=290K. Turbulence flag generators were used to turbulize the free stream. The root-mean-square values of the turbulized flow longitudinal velocity component fluctuations were <U' 2>05/(7o=0.03-19.8, and an integral scale of the turbulence was L=58 m m . During the experiments measurements of velocity fluctuations both inside the dimple and around it, a wall shear stress, and a heat flux onto the wall inside the dimple were carried out. Velocity U and a wall shear stress x were measured by miniature hot-wire probes and DISA 5 5 M anemometer. A special hot-wire anemometer sensitive to the flow direction [9] was utilized for measurement of U and x in recirculating flows. Measurements of the local heat fluxes on the dimple surface were made using a heat flux probe [10]. The experimental equipments and measurement techniques are outlined in [8] in more detail. To perform the experimental investigations of combustion process and flame stabilization, the other experimental installation was used. Its working section constituted a channel with rectangular cross-section of 8 4 3 m m x 100mm. The channel height H could be varied from 5 m m to 100 m m via separable inserts. The construction of the working section allowed to deflect its upper wall at the angle of 0 = ±11° (Figure 3). As this takes place, the influence of the pressure drop on the flow pattern and combustion might be investigated. The working section wall and other elements of the air channel of the installation were made of stainless steel. A double-stage convergent nozzle with the area ratio 9:1 was positioned at the working section entry. The upper wall and one of the side walls of the working section could be substituted for a transparent glass. This allowed to visualize the flow and combustion as well as to take pictures. A hemispherical dimple, placed mounted flush with the lower wall surface of the working section was the subject of the investigation. The dimple diameter was c/=50 m m , and its relative depth - h/d=0.5. The dimple was made of stainless steel with 10 m m wall thickness. Four holes with diameter 2.5 m m (Figure 4) were made in the dimple wall at the depth of h=0.25d from the pole, namely, the lower point. T w o of them were designated for natural gas supply, while die others - for aluminium powder injection to visualize the flow. 4 |