BellDüse

BellDüse, commonly referred to as a bell nozzle, is a rocket engine nozzle with a bell-shaped contour designed to expand exhaust gases efficiently over a range of ambient pressures. The bell shape helps reduce losses from flow separation and pressure mismatch, improving thrust and specific impulse, particularly at higher altitudes or in vacuum.

Design and operation: The nozzle has a throat where the gas reaches sonic speed, followed by a curved exit section whose profile aims to maintain favorable expansion as external pressure drops. Compared with a simple conical nozzle, a well-contoured bell nozzle better matches the internal flow to the external pressure, reducing kinetic energy losses and improving overall performance.

Variants: Classical bell nozzles are complemented by extended bell and dual-bell designs. Extended bell nozzles continue the expansion of the flow for better vacuum efficiency, while dual-bell nozzles feature two expansion segments to optimize performance across a wide range of ambient pressures, from sea level to space.

Applications and performance: Bell nozzles are widely used in liquid-fueled rocket engines, especially on upper-stage engines where ambient pressure is low. They can be heavier and more complex than conical nozzles, and their performance gains depend on the engine’s operating regime and design tolerances.

History: The concept emerged as engineers sought improved exhaust expansion in the early to mid-20th century. Since then, bell contours have become a common feature in modern rocket propulsion, alongside other contoured nozzle designs, as part of efforts to maximize efficiency across varying flight conditions.