ENGR 4011 Resistance & Propulsion of Ships Assignment 5: A dimensional analysis of propeller thrust starting with the functional expression

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1 ENGR 40 Resistance & Propulsion of Ships ssignment 5: 07. -dimensional hydrofoil section is shown below. It has an incidence velocity V incidence at an angle of attack α E. For the case shown: sketch the pressure distribution over both sides of the section, indicating where the pressure increases and decreases compared to the free stream pressure; show where the stagnation pressure will be likely to occur; show where you might expect cavitation to occur; illustrate the zero lift angle and zero lift line. α E V incidence. dimensional analysis of propeller thrust starting with the functional expression can yield a b c d e f g [ ρ,d,v,g,n, p, ] µ φ eqn. ρd V Dg nd p φ,, V V ρv υ, VD eqn. Explain briefly the significance of each of the four terms on the right hand side of the second equation and state the relevance of each to model propeller open water performance testing. Brian Veitch, EN0c, el: , bveitch@mun.ca ass5-07.doc

2 3. hydrofoil with span b, and chord length c is used to provide the lift for a human powered boat. he boat and rider have a combined mass of 0kg, which the foil has to support when the boat is foil borne. n initial design of the foil has a span of.40m and a constant chord length of 0.30m. D lift data for the section used in the foil is available as shown below. ssuming the foil has no losses at the tips or elsewhere, give a speed and angle of attack combination for which you can estimate the boat to go from hull borne to foil borne. In subsequent trials at the condition you chose, what would expect to actually happen and explain why the trials performance would differ from the performance predicted using D data? lift coefficient [-] angle of attack [degree] 4. Describe briefly each of the following types of propeller, using a sketch to illustrate your answer. controllable pitch propeller waterjet propeller podded propeller surface piercing propeller cycloidal propeller

3 5.a) You are tasked with doing a preliminary design for a 3 knot displacement ship with a length of 9m, draft of 7.0m, and breadth of 6.5m. Model scale resistance and self-propulsion tests have been done on the hull form, which has a twin screw propeller arrangement. he tests showed that the ship resistance to be expected at the design speed is 554kN. Wake fraction and thrust deduction fraction were found to be 0.4 and 0.6, respectively. he hull form can accommodate twin propellers with a maximum diameter of 5.70m. Using the attached standard series chart of B4-85 propellers, find a P/D ratio that will provide the thrust required to reach the design ship speed at a shaft speed of 70 rpm. Estimate the open water propeller efficiency η o and the hydrodynamic propulsive efficiency η D at the design condition. Pass in the chart with your exam. lso, calculate the total installed propulsion power (c ) required (for both shafts) if the shaft efficiency η S is 99%, the gear efficiency η M is 96%, and the diesels are to be run at 90% of their maximum continuous rating at the design ship speed (i.e. derating d r is 0.90). ssume the water temperature is 5 C. 5.b) Check the propeller selected in 5.a) above for cavitation using Burrill s method (use the attached sheet). Show all work and pass in the chart with the exam. he vapor pressure of water can be taken to be 4 kpa, and the atmospheric pressure is 0 kpa. he depth of the hub from the free surface is 4.0 meters. pproximately how much back cavitation can be expected to occur? 5.c) What are three negative effects of cavitation? If a preliminary propeller design is found to be likely to cavitate to an unacceptable extent, what are two design changes that might be implemented in order to reduce cavitation and/or mitigate the effects of cavitation? Explain how each design change would reduce cavitation and/or mitigate its effects. 3

4 ypical exam equation & data sheet for ENGR-40 C R ρv S VL υ c 0.75R V + ( 0.75πnD) υ C F ( log 0 ) C! VL $ F 0.07# & " υ % 0.! C F.37 VL $ # & " υ % 0.5 P E RV P V πnq η S η M C S ( + k)c FS + C M ( + k)c FM + C + C L W π V g J V nd η o K J πk Q V V S ( w) R t η D η H η B P E ( ) η η H η B η S η M + x d r P E c P E P K ρ n D K Q 4 Q ρ n D δ 0.37x! υ $ # & 5 " Vx % ρv + p ρv + p F n V gl /5 P P S P S s s c Equations for Burrill's chart σ 0.7R p o p v ρ V + 0.7πnD ( ( ) ) τ c p q 0.7R p E Constants and data knot m/s g9.806 m/s υ m /s ρ 999 kg/m 3 5 C) υ m /s ρ 05 kg/m 3 5 C) 4

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