טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentNahomu Kameda
SubjectEjector Working against High Back Pressure
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Emeritus Wolfshtein Micha
Dr. Eliezer Spiegler


Abstract

The performance of a supersonic axi-symmetric divergent-convergent ejector operating against high backpressure is investigated using the INCA computer code. Although the structure of the ejector is simple, the flow regime may be very complicated due to the interaction between super and subsonic flows, high-pressure differences, and turbulence. The goal of the present research is to obtain a general description of the operation of an ejector near limiting pressure ratio by a numerical investigation of the flow in such devices.

The computations utilized the commercial INCA CFD computer code. This code employs the Yee Symmetric TVD flux function to the non-viscous fluxes, and central differences for the diffusive fluxes, the implicit LU-SGS Lower-Upper Symmetric Gauss-Seidel for the solution of the linearized system of discrete equations. A low Reynolds number energy-dissipation model is used to account for the effects of turbulence.

Parametric runs revealed the various regimes of operation of the ejector. Two major regimes were found, namely supersonic solution with high primary pressure, and mixed (supersonic/subsonic) solution with low primary pressure. Between these two regimes a third regime was found where hysteresis effects dominated with two branches of the solution, depending on the initial conditions for the solution. In the intermediate regime various modes were observed, of steady or periodic character. The solution obtained in this branch depends strongly on the nozzle to cylinder distance. Thus an optimal value of this parameter exists, ensuring best flow rate and stability of the flow in the low-pressure regimes.