Predicting axial velocity profiles within a diffusing marine propeller jet

Abstract

12A full understanding of the hydrodynamic processes within the jet produced by a manoeuvring 69fully understood if an engineer is to be able to quantify any scouring damage that may occur, 70and, more importantly, size protection systems to be deployed to prevent further damage. 72The flow field produced by the action of rotating propeller blades is complex in nature. Near 73to the propeller, the passing blades and rotating hub influence the characteristics of the flow. 74As the jet diffuses downstream, the velocity characteristics become similar to a submerged 102The propellers used in this investigation varied in size (Dp), numbers of blades (N), pitch to 103 diameter ratios (P'), thrust coefficients (Ct), rake and blade area ratios (β), as shown in Table 104 1. The number of propeller blades varied from three to six. The pitch to diameter ratio ranged 107The blades of propeller 1, 3 and 4 had no forward inclination i. Equation 3 124 125The rotational speeds used in the programme of work were based on standard Froudian scale 134The propellers were operated across a range of speeds that bounded these target values, 135and these are listed in full in Table 2. 137The Reynolds numbers for the propellers operating at these rotational speeds ranged from 138

Ship Twin-propeller Jet Model used to Predict the Initial Velocity and Velocity Distribution within Diffusing Jet

“…Eq. 11from Hamill (2016) is recommended to predict the maximum axial velocity decay within ZFE-TP-4P by comparing the numerical value in Fig 7. The variation between the experimental results and the numerical result is in an acceptable range within the zone downstream of x 3.5 . Eq.…”

“…Hamill et al (2015) investigated the efflux velocity from four different propellers operating at four rotational speeds and made comparison with the previous works. Hamill et al (2016) proposed the semi-empirical equations to determine the location, magnitude and distribution of the axial velocity within a free expanding propeller jet. Mujal-Colilles et al (2017) measured the velocity distribution within a twin-propeller jet using Acoustic Doppler Profiler (ADP) and suggested Blaauw et al's (1978) equation well agreed with the experimental results.…”

Scour Induced by Single and Twin Propeller Jets

“…Hamill et al [3] started the research on propeller jets according to the axial momentum theory and plain jet theory. Hamill et al [17] found that the flow structure of the propeller jet is symmetrical along the rotational axis. The jet can be divided into two development stages, which are the zone of flow establishment and zone of established flow and the whole jet is conical in 3D view.…”

Temporal Model for Ship Twin-Propeller Jet Induced Sandbed Scour

“…The coefficients for second term are calculated to obtain B = 0.1571 and C 2 = 0.3376 with R 2 = 0.736. The empirical corrections can be inserted into Equations (16)- (18) and then proposed the empirical model of twin-propeller used to estimate the time-dependent scour depth by using Equations (20)- (22).…”

“…The proposed equations have a high correlation with the experiment data, with the R 2 = 0.917. Equations (16)- (18) and then proposed the empirical model of twin-propeller used to estimate the time-dependent scour depth by using Equations (20)- (22).…”