CIVE09014 Fluid Mechanics 3 Civil

1. CIVE09014Fluid Mechanics 3 (Civil) Session 2011-2012

3. Course Resources See Web CT - Make sure you are correctly matriculated for the course Temporary url at www.eng.ed.ac.uk/~martc Course reference: Chadwick, Morfett and Borthwick Hydraulics in Civil and Environmental Engineering 4th Edition, Spon Press. I follow this closely and it is a good investment. Almost all calculations are iterative or similarly irritating � solving cubics, etc, and are amenable to use of Excel (or possibly Matlab). Tutorial solutions and examples are done on Excel For this reason the exam will be in the computer lab and will allow electronic submissions either in addition to or instead of paper ones. The exam will also be open book (but beware of this).

4. Teaching Philosophy http://www.eng.ed.ac.uk/~martc/teaching/teachingphilosophy.html Not my intention that you note down everything on the slide You do need to note verbal commentary as well as things that appear in writing Worked examples must be taken as a whole including verbal commentary Worked examples including verbal commentary are my only source of information on presenting good exam answers

5. Pipe Systems Introduction Brief revision of 2nd Year material General Principles of Pipe Flow Solutions for Single Pipes Pipe Networks Pumping Mains Sewer Systems

6. Engineering Significance Pipe systems are very important in civil engineering Water supply Storm water drainage Foul drainage Oil pipelines, etc

7. Laminar and Turbulent Flow http://www.youtube.com/watch?v=nl75BGg9qdA Reynolds No: Laminar flow: Re < 2000, hf a v Transitional flow: 2000 < Re < 4000 Turbulent flow: Re > 4000, hf a v2 The values of Re are for pipes � different values apply to channels.

8. Brief Revision of 2nd Year Material Fluids and Viscosity Hydrostatics Streamlines, manometers Drag on bodies Bernoulli�s Equation Momentum Equation Real Flow in Pipes

9. Real Flow in Pipes - Friction Darcy-Weisbach equation Colebrook-White equation for friction factor

10. Derivation of the Friction Factor Laminar Flow: When the flow is laminar, relative roughness has no influence on the friction factor. Laminar flow can be described by the Hazen-Poiseuille equation:

12. Boundary Layer

13. The Colebrook-White Transition Formula Is applicable to the entire turbulent flow region Requires a trial and error solution, and this restricted its widespread use when it was first introduced Other simpler formula eg Hazen-Williams and Manning are still used (with different friction factors) � see in a minute.

15. Typical ks Values

18. Other Pipe Flow Formulae and Principles Four factors � flow rate, hydraulic gradient, diameter, friction losses We typically know three and need the other one All formulae available relate these Friction losses are related to Re � but Manning and Hazen Williams neglect this making them less accurate

19. Hydraulic Gradient Line and Energy Line

20. Pipes can flow under pressure or under gravity Former case is usual for water supply In normal conditions sewers flow under gravity When flow is gravity flow, friction loss will be exactly balanced by height loss Slope needed will be the geometrical slope When flow is under pressure it is the hydraulic gradient that is needed which will not necessarily be the same as the geometrical slope Pressure and Gravity Flow

21. Second Year Examples

22. Pipe Networks Most piped water distribution systems comprise networks of pipes in series, in parallel, in branched networks and in loops.

23. Networks - Pipes in Series Q1 = Q2 =Q from continuity hf1 and hf2 unknown Guess Q and solve iteratively

24. Networks - Pipes in Parallel H = hf1 = hf2� Q = Q1 + Q2

25. Networks - Branched Pipes Q1 + Q2 = Q3 hf1 = z1 � Hj Guess Hj and solve iteratively hf2 = z2 - Hj hf3 = Hj � z3

26. Examples Simple Series Parallel Reservoir

27. Pipe Loops Pipe loops are common in water distribution systems. Basic principles Loops and nodes Examples

28. Basic Principles Pipe network divided into loops with nodes

29. At each node, continuity may be applied: Around any loop, the sum of head losses must be zero:

30. Also, in each pipe, head loss is a function of discharge as is evident from all pipe flow formulae Sign Convention (very important!) Flows into a node are positive Head loss clockwise round a loop are positive

31. Hardy-Cross Method The "loop" or "head balance" method This is used when the total volume rate of flow through the network is known but the heads or pressures at junctions within the network are unknown. The "nodal" or "quantity balance" method This is used when the heads at each flow entry point are known and it is required to determine the pressure heads and flows through the network.

32. The Loop Method assume values of qi to satisfy calculate hfi from qi if then solution is correct if then apply a correction factor and return to step 2 � Correction factors can be computed from: (see p411) �

33. The Nodal Method assume a value of head Hj at each junction calculate qi from Hj if then solution is correct if then apply a correction factor and return to step 2 � Correction factors can be computed from: �

34. Examples Simple Problem More Complex Problem Reservoir Problem Finding heads at multiple nodes

35. Trunk Main Design Practical Considerations Example of Design

36. Practical Considerations

37. Pipe should remain below energy line to keep pressure above atmospheric otherwise cavitation risk Provide air valves at high points to release air during filling and operation Provide washout valves at low points for drainage for maintenance Provide Break-Pressure tanks as necessary Provide thrust blocks for reinforcement where velocity changes

38. Basic Strategy Assume pipe diameter Calculate head loss in pipe for required flow Determine any significant losses at fittings Head loss in pipe must be balanced by head available � adjust diameter until a suitable value is reached giving balance Determine max (and perhaps min) pressure in pipe Consider break pressure if needed Determine pipe material spec needed to withstand pressure Specify required thrust blocks, valves etc

39. Pumping Main Design Hydraulic Design Pumps in Series Pumps in Parallel Example

40. Hydraulic Design Pumping adds head to the system. Hence: Hp = H + hfs + hfd s=suction, d=delivery

41. Pumps in Series The head increases for a given discharge: Hnp = nHp Qnp = Qp

42. Pumps in Parallel The discharge increases for a given head: Hnp = Hp Qnp = nQp

45. Maintenance Issue Pumps in series cannot be maintained without shutting down the system. Pumps in parallel can have one pump switched off but leave the other working.

46. Example 1 Given the pump characteristics below, determine the pump efficiency and power requirement for a pipeline of diameter 150 mm, length 250 m, Hazen-Williams Rougness of 120, and static lift of 10 m. Comment on the suitability of this pump and pipeline combination.

47. It is required to lay a pipeline over some hills. The elevation at the start is 0, at the end at chainage 43km it is 23.08m and the maximum elevation at chainage 23km is about 65m. The required flow is 40�106 litres/day. Pump characteristics for one pump are the same as follows: Determine suitable size of pipe and the head required to be produced by the pumps State your assumptions. Example 2

48. Surge Protection Surge refers to dynamic forces such as those that occur when a valve is closed or a pump fails The kinetic energy of the flow has to go somewhere: if the flow stops it needs to dissipate It might do this by destroying something! Surge protection allows energy to dissipate safely Fuller coverage in 4th year Hydraulics

49. Surge Towers and Tanks

50. Pumping Stations Typical application in sewer system Inflow may not be constant Arrangement with sump with start and stop levels Pumps start when water reaches start level and work until it drains down to the stop level Want to control number of starts and stops for wear and tear This involves a storage calculation

51. Sewer Networks and Controls General Arrangement Combined and Separate Systems Manholes Dry Weather and Storm Flows Surcharging and Flooding CSOs and UIDs Storage and controls Typical problems for the engineer

53. Combined Sewer Overflows Unsatisfactory Intermittent Discharges

57. Formula �A� How much can a CSO operate? Formula A = DWF+1360P+2E (m3/day) DWF=P+I+G (m3/day) P=population G=per capita return to sewer flow (m3/hd/day) I=infiltration (m3/day) E=trade effluent (m3/day) Amount of overflow allowed depends on upstream catchment Frequency of operation is also an issue

58. Detention Structures A Structure created to detain storm water until peak of flow is passed and then release it slowly Reduces flooding Ponds, Tanks Online or Offline Controls to, well, control the outflow

61. Controls Controls Include: Hydrobrakes Orifice Plates Weirs The downstream pipe All have a fixed head/discharge relationship Q=f(h)

63. Typical Sewer System Problems for the Engineer Flooding UIDs Upgrading required Investment must be targeted: Asset Management Plan (England) Strategic Review (Scotland) Key point is to understand a system and its controlling influences

67. References Chadwick and Morfett Chapter 4 � the basics, mostly covered in 2nd Year Chadwick and Morfett Chapter 12 up tp page 385