Simulating cross altitude performance of expansion deflection nozzles
- Paper number
IAC-06-C4.5.07
- Author
Dr. Neil Taylor, University of Bristol, United Kingdom
- Year
2006
- Abstract
Air-breathing propulsion systems, and in particular single stage to orbit vehicles, require efficient nozzle systems across a wide range of ambient pressures, in order to maximise the impulse delivered. However, conventional bell designs with fixed area ratios only perfectly expand at a single ambient pressure, and at all other times, the nozzle is operating less efficiently. Furthermore, the need to avoid separation at sea level conditions may also limit expansion ratio, and thus efficiency in vacuum.
The Expansion Deflection (ED) nozzle offers the potential to overcome these difficulties through a central void in the flow which allows the ambient pressure to form the internal boundary of the primary nozzle flow. This means that in theory the flow will perfectly expand at all pressure ratios up to the maximum allowed by a full flow, and thus improve efficiency, and remove area ratio limits. However, this advantage comes at the cost of significantly increased complexity within the nozzle flowfield. Historically, this complexity has lead to few serious attempts to analyse atmospheric flow performance of the ED type. This paper summarises one such method developed at the University of Bristol, which makes use of a mixed computational, analytical, and empirical approach to calculate the altitude performance of the type.
However, it is understood that the method as described is imperfect, as significant viscous effects are ignored, and boundary layer-shock wave interactions are not calculated. Furthermore, the effect of vehicle motion and the well-known evacuating tendency of the primary supersonic flow on the central void are not fully accounted for. It is shown that these effects may be incorporated into standard trajectory modelling as an efficiency factor acting on the exit pressure term, in effect causing the nozzle to expand to a virtual altitude greater than that of the vehicle. Experimental data is used to estimate this factor, and a typical launch trajectory of a single stage to orbit vehicle is used to analyse not only the potential benefit of an ideal ED nozzle, but also the impact on the result of variation in the efficiency factor. It is found that such an altitude compensating device, if operating perfectly, has potential to increase payload by up to 5
- Abstract document
- Manuscript document
IAC-06-C4.5.07.pdf (🔒 authorized access only).
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