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Research Papers: Flows in Complex Systems

# Experimental Investigation of the Submarine Crashback Maneuver

[+] Author and Article Information
David H. Bridges

Department of Aerospace Engineering, Mississippi State University, Mississippi State, MI 39762

Martin J. Donnelly, Joel T. Park

Naval Surface Warfare Center, Carderock Division, E. Bethesda, MA 20817

J. Fluids Eng 130(1), 011103 (Jan 16, 2008) (11 pages) doi:10.1115/1.2813123 History: Received October 04, 2006; Revised August 17, 2007; Published January 16, 2008

## Abstract

In order to decelerate a forward-moving submarine rapidly, often the propeller of the submarine is placed abruptly into reverse rotation, causing the propeller to generate a thrust force in the direction opposite to the submarine’s motion. This maneuver is known as the “crashback” maneuver. During crashback, the relative flow velocities in the vicinity of the propeller lead to the creation of a ring vortex around the propeller. This vortex has an unsteady asymmetry, which produces off-axis forces and moments on the propeller that are transmitted to the submarine. Tests were conducted in the William B. Morgan Large Cavitation Channel using an existing submarine model and propeller. A range of steady crashback conditions with fixed tunnel and propeller speeds was investigated. The dimensionless force and moment data were found to collapse well when plotted against the parameter η, which is defined as the ratio of the actual propeller speed to the propeller speed required for self-propulsion in forward motion. Unsteady crashback maneuvers were also investigated with two different types of simulations in which propeller and tunnel speeds were allowed to vary. It was noted during these simulations that the peak out-of-plane force and moment coefficient magnitudes in some cases exceeded those observed during the steady crashback measurements. Flow visualization and LDV studies showed that the ring vortex structure varied from an elongated vortex structure centered downstream of the propeller to a more compact structure that was located nearer the propeller as η became more negative, up to $η=−0.8$. For more negative values of η, the vortex core appeared to move out toward the propeller tip.

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## Figures

Figure 2

Submarine hull contour; sail not used in experiments but indicates location of strut

Figure 3

Illustration of propeller, stern appendage placement, and stabilization strut

Figure 4

Body rms yawing moment coefficient (based on propulsive scaling)

Figure 5

Propeller rms side force coefficient (based on propulsive scaling)

Figure 6

Propeller rms resultant force coefficient (based on propulsive scaling)

Figure 7

Comparison of propeller rms horizontal force coefficient values with and without restraint strut

Figure 8

Dimensionless frequency of peak propeller y force amplitude (u∕r—restraint strut off /on)

Figure 9

rms propeller side force development for ramped propeller speed simulation of unsteady crashback

Figure 10

Development of rms propeller y force and rms body pitching and yawing moments during constant tunnel velocity, ramped propeller speed simulation of unsteady crashback maneuver (values normalized by maximum data value in each set)

Figure 11

Development of rms propeller y force during ramped tunnel velocity, ramped propeller speed simulation of unsteady crashback maneuver

Figure 12

Development of rms propeller horizontal force and rms body yawing moment during unsteady crashback maneuver simulation

Figure 13

Comparison of coefficients of rms propeller y force between unsteady crashback conditions and the minimum and maximum values of the three ramped tunnel velocity, ramped propeller speed simulations of the unsteady crashback maneuver

Figure 14

Comparison of coefficients of rms body yawing moment between steady crashback conditions and the minimum and maximum values of the three ramped tunnel velocity, ramped propeller speed simulations of the unsteady crashback maneuver

Figure 15

Summary of LDV velocity field surveys for η=−0.801 (in coordinates shown, propeller tip would be located at x=809.2mm, z=152.4mm)

Figure 16

Vortex center positions estimated from LDV measurements (downstream direction is to the right in this figure)

Figure 17

Velocity components at complete survey position nearest propeller for η=−0.80

Figure 1

Schematic of flow (velocities in reference frame of submarine in forward motion)

Figure 18

Comparison of “formed vortex” positions at different values of η: (a) η=−0.387, (b) η=−0.580, (c) η=−0.725, (d) η=−0.825, (e) η=−1.09, and (f) η=−1.52

Figure 19

Examples of large-scale disturbances to vortex flow for η=−0.780: (a) vortex shedding event and (b) large-scale disruption

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