Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
  • F15D1/00—Influencing flow of fluids
  • F15D1/002—Influencing flow of fluids by influencing the boundary layer
  • F15D1/0065—Influencing flow of fluids by influencing the boundary layer using active means, e.g. supplying external energy or injecting fluid
  • F15D1/007—Influencing flow of fluids by influencing the boundary layer using active means, e.g. supplying external energy or injecting fluid comprising surfaces being moved by external supplied energy
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
  • F15D1/00—Influencing flow of fluids
  • F15D1/02—Influencing flow of fluids in pipes or conduits
  • F15D1/06—Influencing flow of fluids in pipes or conduits by influencing the boundary layer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
  • F17D1/00—Pipe-line systems
  • F17D1/20—Arrangements or systems of devices for influencing or altering dynamic characteristics of the systems, e.g. for damping pulsations caused by opening or closing of valves

Definitions

• the present invention generally relates to a method of and an apparatus for eliminating turbulence in a wall bounded flow.
• a wall bounded flow i.e. in a flow of a fluid over a wall
• the wall exerts shear forces onto the fluid, and, as a result, a boundary layer of the flow is formed at the flow-bounding wall in which the flow is affected by the wall.
• the flow may be laminar or turbulent, the drag in a boundary layer being much higher with a turbulent flow than with a laminar flow.
• a laminar flow often has big advantages over a turbulent flow in that it saves energy, like for example in pumping a liquid through a pipe or channel.
• Hof et al. point out, that a distortion of the velocity profile at the turbulent laminar interface cannot be as readily implemented in practice as in simulations.
• the present invention relates to a method of eliminating turbulence in a wall bounded flow, the method comprising the step of moving a section of the flow-bounding wall in the direction of the flow over the flow-bounding wall.
• the present invention relates to an apparatus for eliminating turbulence in a wall bounded flow, the apparatus comprising a drive unit moving a section of the flow-bounding wall in the direction of the flow over the flow-bounding wall.
• Fig. 1 illustrates the general concept of the new method
• Fig. 2 is a graph of measurement data indicating the effect of the new method
• Fig. 3 is a graph of further measurement data obtained at a higher Reynolds-number than Fig. 2 and also indicating the effect of the new method;
• Fig. 4 shows a first embodiment of an apparatus for implementing the control region of Fig. 1 ;
• Fig. 5 shows a second embodiment of an apparatus for implementing the control region of Fig. 1.
• a part or section of the flow-bounding wall is moved in the direction of the flow over the flow-bounding wall.
• the fluid in the boundary layer of the flow which is located close to the flow-bounding wall is accelerated as compared to its velocity of zero with a fixed flow- bounding wall.
• this results in a distortion of the velocity profile in that the maximum difference in velocity between the fluid in the boundary layer directly adjacent to the flow-bounding wall and the fluid in the centre of the flow or even outside the boundary layer is reduced.
• the shearing forces in the boundary layer feeding turbulence are reduced.
• the new method is not only able to avoid the occurrence of turbulence but also to re-laminarize an already turbulent flow. If the flow is not disturbed again downstream of the point at which the new method is executed, it may stay laminar indefinitely (Reynolds-number permitting). Thus, a local application of the new method may reduce the drag of a flow over a very long distance, like for example an entire pipe or channel. In this way, the new method may be used to strongly decrease the energy spent for pumping fluids like gases and liquids.
• the moved section of the flow-bounding wall preferably essentially includes the full flow-bounding wall bounding the flow over a length of the flow. I. e., over this length of the flow there are preferably no parts of the flow-bounding wall which are not moved in the direction of the flow.
• the suitable length of the flow over which the moved section should include the full flow-bounding wall will depend on the velocity at which the section of the flow-bounding wall is moved. Generally, this length of the flow should be at least about 20, preferably at least about 25 and more preferably at least about 30 boundary layer thicknesses long. In this context the boundary thickness layer may be defined as the thickness over which the flow- bounding wall affects the flow. If the flow-bounding wall encloses a lumen through which the flow flows, like in case of a pipe or a channel, the moved section of the flow-bounding wall generally is at least about 20, preferably at least about 25 and more preferably at least about 30 diameters of this lumen long.
• the length of the flow over which the section of the flow-bounding wall which is moved in the direction of the flow according to the invention should extend may depend on the velocity at which the section is moved. Generally, this velocity should be at least about 40 %, preferably at least about 50 % and most preferably at least about 60 % of an average flow velocity of the flow over the unmoved flow-bounding wall. However, even with lower velocities of the moved section of the flow-bounding wall than 40 % of an average flow velocity of the flow the laminarization effect may be achieved.
• the velocity of the moved section of the flow-bounding wall may, in principle, even be higher than the average flow velocity over the unmoved flow-bounding wall. Preferably, however, this velocity is at maximum about the same as the average flow velocity over the unmoved flow-bounding wall which makes implementation of the present invention much easier with very quick flows.
• the moved section of the flow-bounding wall may be a partial cover of the overall flow-bounding wall.
• it may be a film covering a part of the flow-bounding wall.
• Such a film can be circulated in a closed loop, a feed back branch of the film loop running outside the area of the flow.
• the moved section of the flow-bounding wall is a liner of a section of this lumen.
• This liner may be moved in the direction of the flow out of an initial position into an end position, and afterwards be retracted back into its initial position. This retracting may take place at a time at which the flow is not flowing over the flow-bounding wall or it may take place at much lower velocity against the direction of the flow than in the direction of the flow when turbulence in the flow is to be laminarized.
• This embodiment of the invention is well-suited for such cases in which the turbulence in the flow to be re-laminarized does not permanently occur.
• the new method easily works with high Reynolds-numbers above 3000, 4000 or even above 5000.
• the new apparatus for eliminating turbulence in a wall bounded flow comprises a drive unit moving a section of the flow-bounding wall in the direction of the flow over the flow- bounding wall. Most of the details of the new apparatus correspond to the details of the new method already described.
• the present invention is applicable to flows only bounded by the flow-bounding wall in one direction like a flow over a surface of an aeroplane or submarine.
• the invention is of particular interest with flows through pipes and channels.
• the moved section may be a partial liner of the pipe or channel.
• this partial liner may be a film tube or consist of a plurality of film bands lining a part of the pipe or channel.
• Fig. 1 shows a pipe 1 through which a fluid 2 flows in a flow direction 3.
• the fluid 2 displays a turbulent flow 6.
• this turbulent flow 6 is laminarized such that a laminar flow 7 leaves the control region 5 and stays laminar with the typical parabolic velocity profile 8 over the cross section of the pipe 1 in a part 9 of the pipe 1 downstream of the control region 5 as long as the laminar flow 7 is not disturbed for turbulence again.
• the method according to the present invention laminarizing the flow in the control region 5 of Fig. 1 is not yet active ("Control off”). Then the method is started ("Control on”). As a result, the drag of the flow indicated by the normalized pressure difference drops to the drag or pressure difference of a laminar flow.
• laminarizing the flow in the control region 5 reduces the drag of the flow through the downstream part 9 of the pipe 1 by more than a factor of two.
• Fig. 3 is another graph of a pressure difference ⁇ measured over a length of the part 9 of the pipe 1 according to Fig. 1 and normalized to the pressure difference Api am inar Of a laminar flow through the part 9.
• the further details of the measurent and the basic result are the same as in Fig. 2.
• the effect of the present invention at the higher Reynolds-number is even higher: Laminarizing the flow in the control region 5 reduces the drag of the flow through the downstream part 9 of the pipe 1 by a factor of 3,5 here.
• Fig. 4 shows the particular set up of the control region 5 with which the data according to Fig. 2 and Fig. 3 have been obtained.
• a pipe section 10 partially lining the pipe 1 is moved along the axis of the pipe 1 in the flow direction 3.
• the wall 1 1 of the pipe section 10 fully encloses the fluid 2 within the pipe 1 in radial direction, i.e., the wall 11 is the entire flow-bounding wall 12 in the area of the pipe section 10.
• the liner 10 defines that section 13 of the flow-bounding wall 12 which is moved in the flow direction 3 through the pipe 1 according to the present invention, and it may also be designated as a liner 14 of the pipe 1 .
• the relative length of the section 13 indicated in Fig. 4 is too short. In the experiment producing the results indicated in Fig. 2 the length of the section 13 was about 60 times the diameter of the pipe 1.
• Fig. 5 shows another embodiment of the control section 5 in the pipe 1.
• the liner 14 of the pipe 1 is made of film bands 15 running as closed loops 16 around rollers 17 which are located outside the pipe 1.
• the moved section 13 of the flow- bounding wall 12 stays in place, i. e., it does not move along the pipe 1 , although the parts of the film bands 15 in contact with the fluid 2 move in the flow direction 3.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)

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Citations (2)

• 2011
  • 2011-11-22 EP EP11794422.3A patent/EP2643597A1/de not_active Withdrawn

Patent Citations (2)

Non-Patent Citations (1)

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