Effect of swirl on the turbulent behaviour of a dump combustor flow

Abstract

This article reports an experimental investigation of non-reacting flow in a low aspect ratio dump combustor with a tapered exit. The length of this combustor was less than the separated flow reattachment length. The turbulent intensity variation inside the combustor without swirl was found to be axi-symmetric. The turbulent intensity increases in the shear layer between the potential core and the recirculation eddy. The intensity in the core region increases as one moves along the centre-line in the axial direction. The turbulence behaviour significantly changed with the use of a swirler at the inlet of the combustor. The average turbulent intensity increased inside the combustor and the differences in the magnitude of the intensity along the axial and radial directions were less compared to the non-swirling flow. For a high swirl number (( SN) = 1.48), the intensity in the core region was higher compared to other regions inside the combustor. The intensity variation inside the combustor was more uniform than in the case of the low swirl number flow. The r.m.s. velocity studies also suggest more turbulence generation due to swirl. The presence of the swirler increased the turbulence kinetic energy and dissipation rate in the central vortex core region. The power spectral density distribution shows the alteration of the frequency content of the power spectrum, which can be attributed to the forced recirculation due to swirl. The effect of a high swirl number and Re on the frequency peak shows similar behaviour. Therefore, turbulence inside the combustor increased due to the swirler; hence, better mixing of the fuel and air and efficient and stable combustion is expected to be achieved.

Flow dynamics in low aspect ratio dump combustor

“…However, the physics of the flow dictates that the flow has to confirm to the no-slip boundary condition at the wall. It been reported earlier that there is an expansion or acceleration of the flow as it emerges from the inlet pipe to the dump combustor resulting in the formation of a potential core where the mean axial velocity at the vicinity of the centerline is greater than the velocity at the inlet pipe, as has been explained in [34,35]. Now, in order to conserve the overall mass flow rate, the flow has to reverse its direction somewhere inside the combustor.…”

“…The data were analyzed using a MATLAB s 7.0.1 code. The hotwire probe was oriented perpendicular to the combustor axis and was inserted radialy into the combustor Figure 2 Schematic of experimental setup for (a) pressure measurement, (b) velocity measurement, and (c) schematic for velocity measurement by hotwire probe [35]. as shown in Figure 2(c).…”

“…The velocity (U) measured by the hot wire is the resultant of u x and u r as shown in Figure 2 (c). Since this hotwire uses a single probe and works on convective heat transfer mode, the total heat loss is equivalent to the heat loss by the effective velocity [35]. As the measured velocities are resultant velocities, the turbulent stresses could not estimated by this method.…”

“…The velocity measured by the hot wire is the resultant velocity because the heat loss by the probe sensor is equivalent to the effective velocity of the flow passing normal to the probe sensor wire from different directions. Since the velocity measured by the probe is the effective velocity, the turbulence intensity was estimated to represent the turbulence [33][34][35]. Pressure measurement by the pressure sensors are used to estimate the fluctuation of the pressure at the inside surface of the combustor.…”

Experimental Investigation of Liquid Jet Breakup in a Cross Flow of a Swirling Air Stream

“…As discussed in [18][19][20], the centrifugal force increases with an increase in the swirl number {S) or swirl vane angle and leads to a greater concentration of flow in the radially outward direction due to the radial pressure gradients. The flow is no longer straight but emerges out from the vane at an angle.…”