The main purpose of this investigation is to establish a relationship between the blowoff velocity of a bluffbody flameholder and its drag coefficient. To this end, numerous measurements of blowoff velocity and drag coefficient are carried out on various forms of two-dimension al flameholders. They include conventional Vgutters of the type widely employed in turbojet afterburners, and "single-sided" flameholders that are characterized by a single-vortex flow pattern in their wake region. The test program covers wide ranges of effective pressure ratio obtained using the water injection technique, and it also includes variations in velocity, flameholder size, and flameholder blockage. The results confirm previous findings in regard to the strong influence of drag coefficient on blowoff velocity. They also provide a satisfactory explanation for the previously reported superior flameholding properties of single-vortex systems over double-vortex systems.

The Relationship Between Flame Stability and Drag of Bluff-Body Flameholders

A theoretical method based on the concept of wall pressure signatures for assessment/correction of wind-tunnel wall interference is presented. The effect of the tunnel wall in upflow and blockage corrections is evaluated by using a thin-layer Navier-Stokes solver. The results for a 65-deg delta wing and a wing-body-strake configuration in subsonic flow are presented. The present prediction of the effects of wall interference on the induced aerodynamic twist and the streamline curvature for the delta wing show a larger magnitude than those by a free vortex sheet method. Two correction charts for the upflow and blockage corrections for configurations with vortex flow are derived based on the computed results for the wing-body-strake configuration at a Mach number of 03. The present method shows consistent corrected results for different model sizes. In general, for a model with strong vortex flow, the present method provides larger corrections than the conventional attached flow theory. The present method can also provide guidelines on where the wall static pressures should be measured in the pressure signature method.

Low-Speed Wall Interference Assessment/Correction with Vortex Flow Effect

The water injection technique is used to determine the blowoff Velocities of bluff-body-stabilized flames supplied with flowing combustible mixtures. The fuels employed include gaseous mixtures of methane, propane, and hydrogen with air. Additional tests are conducted using vaporized gasoline, kerosine (Jet A), and diesel oil (DF2). The apparatus normally comprises a flameholder in the form of a hollow cone which is mounted at the center of a circular pipe with its apex pointing upstream, but in some tests a rectangular working section is used in conjunction with two-dimensional, V-gutter flameholders. The results of the experiments generally confirm theoretical predictions in showing that peak blowoff velocity increases with increase in laminar flame speed.

Influence of laminar flame speed on the blowoff velocity of bluff-body-stabilized flames

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=6748&context=rtd

Effects of Reynolds number and corner radius on two-dimensional flow around octagonal, dodecagonal and hexdecagonal cylinders

A simple method has been proposed to estimate the drag coefficient for bluff bodies in high velocity streams. The estimated values for the drag coefficient agrees well with the measured values. The bluff body shapes considered are the flame holder shapes and blockages employed in jet engine after burners. It has been found that over a range of inlet conditions, the drag coefficient remained fairly independent of Reynolds number. An approximate method of estimating the drag coefficient for staggered flame holder is indicated.

A Method of Estimating Pressure Loss Across Flame Holders in High Velocity Streams

/pdf/a-method-of-predicting-the-aerodynamic-blockage-of-bluff-4ji61dgrvl.pdf

A.H. Lefebvre

Papers

A method of predicting the aerodynamic blockage of bluff bodies in a ducted airstream