Effect of standoff distance and area ratio on the performance of circular exhaust ejector using computational fluid dynamics

Abstract

Numerical investigation is carried out to study the effect of standoff distance and area ratio on mass entrainment of an air–air circular exhaust ejector. Nozzle and mixing tube are the two components of an ejector, and for the present study, circular cross section shape has been chosen. Numerical simulations have been carried out at Reynolds number in the range of 6.85 × 104 and 4.11 × 105. Area ratio is varied between 1.25 < area ratio < 4 and standoff distance is varied from 1 Dnz < standoff distance < 4 Dnz, where Dnz represent the nozzle exit diameter. It is observed that for the ejector configuration with area ratio as 2, 2.25, and 2.5, the mass entrainment characteristics are nearly independent of standoff distance between 1 Dnz to 4 Dnz. For ejector configuration with area ratio below 2, mass entrainment decreases with increase in standoff distance. For ejector configuration with area ratio greater than 2.5, mass entrainment increases with increase in standoff distance for the range investigated and has the tendency to taper off beyond 4 Dnz for most of the area ratios. Effect of change in mixing tube length is also studied. It is seen that the mass entrainment improves with increase in length up to 8 Dnz. Further increase in length does not effect mass entrainment. This study provides important guidelines that can aid in arriving at an optimal design of circular exhaust ejectors.