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Wave Rotor Topping Cycles
for Gas Turbine Engines

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Combustion on the Rotor

Wave rotor cycles which utilize premixed combustion processes within the passages are currently being examined numerically using a one dimensional CFD based simulation. The cycles are envisioned for use as topping cycles in gas turbine engines. The combustion occurs sequentially within the wave channels, each channel being periodically charged and discharged as it rotates past properly sized inlet and outlet ports. By accomplishing combustion on the rotor, the external combustor normally needed in a wave rotor topping cycle is eliminated along with the associated ducting, some of which may be exposed to very high temperatures.

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The current work utilizes a simple representation of combustion that is compatible with the existing One-dimensional Single Passage Simulation model for non-reacting wave rotor flowfields. In this model, one-dimensional computation using a high-resolution CFD technique is performed for a single channel, neglecting interactions between channels. Losses due to the finite passage-opening time, leakage to the casing through the end gaps, heat transfer to the channel walls, and boundary layer viscous losses, are all treated by sub-models which have been validated by experiments. In addition to the CFD treatment of the flow in the channel, the cavities and the channel walls are treated by lumped-parameter models, and the ducts are modeled as steady, constant-area flows to obtain flow homogenization losses. The overall pressure gain is measured by average stagnation quantities computed in the absolute frame of reference, after accounting for the rotational speed effect. The model assumes a calorically and thermally perfect gas with a constant specific heat ratio. The composition of the charge at any time and location is described solely by a reaction progress variable (z) which changes from 1 (pure reactant) to 0 (product) as combustion occurs. Thus, there is one additional equation to be solved, besides the Euler equations of the non-reacting model. A simple representation of turbulence is included in the form of an eddy diffusivity.

The model numerically integrates the equations of motion in a single passage as it rotates past the ports and walls that comprise the ends of the wave rotor and establish the boundary conditions for the governing equations in the passage. Ports are specified by their angular location relative to some fixed point on the wave rotor casing, and by a representative pressure, temperature, and reactant fraction. With each time step the passage advances an angular distance specified by the angular velocity. If the flow is into the passage, the pressure and temperature are interpreted as stagnation values. If the flow is out of the passage, only the port pressure is required, and it is interpreted as a static value


Contact:Daniel E. Paxson
email: daniel.e.paxson@nasa.gov

Project Contact: Daniel E. Paxson
Phone: (216) 433-8334
email: daniel.e.paxson@nasa.gov

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last updated: 2.29.08