THE UNIVERSITY OF ADELAIDE AUSTRALIA SUB CRUCE LUMEN Examination for the Degree of Bachelor of Engineering Semester 2, 2013 MECH ENG 3101 COURSE ID: 104414 APPLIED AERODYNAMICS Official Reading Time: 10 mins Writing Time: 180 mins Total Duration: 190 mins Parts A B Questions Answer all questions Answer all questions Instructions for Candidates Time 110 mins (Recommended) 70 mins (Recommended) 50 marks Marks 75 marks 125 Total · This is an Open Book examination (refer to Permitted Materials). · Answer all questions. · Answer Part A and Part B in separate books and label each book. · Examination materials must not be removed from the examination room. · The marks for each question are indicated. Permitted Materials · Two Pink books. · Notes and textbooks permitted. · Calculator without remote communications capability permitted · Graphics calculator permitted · English language dictionaries are permitted. DO NOT COMMENCE WRITING UNTIL INSTRUCTED TO DO SO
Course ID: MECH ENG 104414 Page 2 of 11 Part A (Total 75 marks) Answer all these questions in an answer book. Clearly indicate "Part A" on the front of the answer book. Useful graphs are given at the end of this question paper. Q1. [25 marks] (a) Water flows into a smooth pipe from a large, still reservoir, as shown in Figure 1. The pipe entrance is rounded with a large radius to prevent separation. The Reynolds number is high, so transition occurs at the inlet and a turbulent boundary layer grows inside the pipe, growing thicker with streamwise distance x. Classical theory tells us that the entry length for turbulent flow in such a pipe is given as follows: Le - 4.4(R 1/ = 4.4(Rep) 6, valid for Rep > 4000. (i) Use boundary layer theory to confirm that this equation is valid. [6 marks] (ii) Discuss whether this analysis should be based on the 99% thickness, the momentum thickness or the displacement thickness. [1 mark] Some relevant turbulent boundary layer equations are: = =0.14R#1/7 Rx , =0.014R X " * x $ =0.0112R#1/7 X x Inlet from still - Core flow reservoir (Irrotational) Boundary layer flow ,No-slip boundary D Entry Length Le Fully developed Figure 1. Pipe Entry region (b) When fully submerged, a military submarine has a maximum speed of 8.6 m/s. The submarine hull has a circular cross-section of nearly constant diameter, with an overall length of 90 m and surface area of 2200 m2. Submarine's surface is extremely smooth to ensure low drag. The submarine is propelled by electric motors with a total capacity of 4 MW. (i) State any assumptions associated with this problem. [1 mark] (ii) Determine whether laminar-to-turbulent transition occurs in the boundary layer on the submarine hull. If transition occurs, where does it occur? [3 marks] (iii) Estimate the 99% thickness of the boundary layer at the aft (downstream) end of the hull. [4 marks] (iv) Estimate the engine power required to overcome skin friction drag on the hull. [5 marks] (v) Estimate the engine power required to