A Practical Approach for Design of Marine Propellers with Systematic Propeller Series
Original scientific paper Although there have been important developments in marine propellers since their first use in 1850, the main concept has been conserved. Parallel to the developments in the computer technologies in the past 50 years, methods based on the circulation theory are often used for the design and analysis of propellers. Due to the ability to predict the propulsion performance with just a few design parameters, the use of systematic propeller series based on open water model experiments is still widespread. The design with standard propeller series is usually made with diagrams developed from model experiments. Reading errors during the use of these diagrams are inevitable. In the presented study a practical approach is developed for preventing reading errors and time loss during the design with standard propeller series. A practical approach based on empirical formulas for the design and performance prediction for four-bladed Wageningen B propeller series is presented, and design applications for three propellers with different loading conditions are realized. The results obtained from the presented method are compared with those of open water diagram data and a good agreement between the results is observed.
Design Procedure of 4-Bladed Propeller
Marine propellers, although submerged in water aft of the ship, form an integral part of a ship and play a vital role in ship propulsion. Much has been said and published on the development of the marine propeller from the time of antiquity to the present age, but there is more to be done. Therefore, this paper focuses on the design procedure of four bladed  marine propellers with specific interest on engines with 85Bhp and ship speed of 30knots for the design of the fixed pitch propeller. This work covers the basic principles underlying the design from the beginning to the end. Thus, this work used the Bp standard chart using the optimum design line to carry out the design analysis of propellers for a ship with a detailed calculation of the various stages involved in the derivation of the basic propeller. The result of the work thus shows that for a propeller with Blade area ratio of 0.55, the open water efficiency is 73%. This means that irrespective of the initial cost of designs and manufacturing this type of propeller, the development of maximum efficiency should be the pursuit of the designer, the manufacturer and the user. Keywords : 4-Bladed propeller, efficiency, pitch ratio, expanded area, developed area, projected area
Turbulent buoyant jets into stratified or flowing ambient fluids
Theoretical and experimental studies were made on two classes of buoyant jet problems, namely: 1) an inclined, round buoyant yet in a stagnant environment with linear density-stratification; 2) a round buoyant jet in a uniform cross stream of homogenous density. Using the integral technique of analysis, assuming similarity, predictions can be made for jet trajectory, widths, and dilution ratios, in a density-stratified or flowing environment. Such information is of great importance in the design of disposal systems for sewage effluent into the ocean or waste gases into the atmosphere. The present study of a buoyant jet in a stagnant environment has extended the Morton type of analysis to cover the effect of the initial angle of discharge. Numerical solutions have been presented for a range of initial conditions. Laboratory experiments were conducted for photographic observations of the trajectories of dyed jets. In general the observed jet forms agreed well with the calculated trajectories and nominal half widths when the value of the entrainment coefficient was taken to be α = 0.082, as previously suggested by Morton. The problem of a buoyant jet in a uniform cross stream was analyzed by assuming an entrainment mechanism based upon the vector difference between the characteristic jet velocity and the ambient velocity. The effect of the unbalanced pressure field on the sides of the jet flow was approximated by a gross drag term. Laboratory flume experiments with sinking jets which are directly analogous to buoyant jets were performed. Salt solutions were injected into fresh water at the free surface in a flume. The jet trajectories, dilution ratios and jet half widths were determined by conductivity measurements. The entrainment coefficient, α, and drag coefficient, Cd, were found from the observed jet trajectories and dilution ratios. In the ten cases studied where jet Froude number ranged from 10 to 80 and velocity ratio (jet: current) K from 4 to 16, α varied from 0.4 to 0.5 and Cd from 1.7 to 0.1. The jet mixing motion for distance within 250D was found to be dominated by the self-generated turbulence, rather than the free-stream turbulence. Similarity of concentration profiles has also been discussed.