JPS6328796A - Hydrodynamic wall surface - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to the deformation of turbulent boundary layer flows over aerodynamic and hydrodynamic surfaces. [Prior Art and Problems to be Solved by the Invention] In recent years, many studies have been conducted regarding the effect of small surfaces on boundary turbulent layers. Particular attention has been paid to the provision of so-called ripplet surfaces with rows of small longitudinal rips extending over the turbulent boundary layer region of the surface in the flow direction of the fluid flowing over the surface, but experimental results have shown no net effect. Alternatively, it has been shown that the surface drag force can be reduced to about 70%. A paper entitled “Drag characteristics of V-grooves and transverse curvature ripples” (presented at the Symposium on Viscous Drag Reduction)
, J. Walsh. Early studies by Liu, Klein, and Johnston (November 7-8, 1979) used rectangular fins to improve the turbulent burst velocity (i.e., the turbulence characteristically formed in steep boundary layer turbulence close to walls). It was noted that drag could be reduced by 6-4% by reducing the burst velocity of low-velocity longitudinal vortices or "streaks".Walsh's paper was a study of an alternative series of lip profiles. reported that they were able to obtain drag reductions of up to 7 degrees using VglJ prets, and this is one of the experimental skin layer friction drag reduction effects that experimenters have been able to obtain to date. The reduction in drag is, for example, rAIAA-83-0377゜AI
AA 21st Space and Space Science Conference J (January 10, 1983-
This is related to the ability of the bullet to restrict the random spanwise movement of the streaks, as has been suggested by a number of sources such as 13th, Leno, Nev., R.E., Faruyu et al. Jonah and Smith (AIAA-85-05
47, AIAA-Shear Flow Control Conference, June 1985, 1
(2-14 days, Boulder, Colorado) established a site of slow streak within a restricted area on a cylindrical replet surface below the height of the V-groove bullet by which Walsh obtained his optimal results. (Moshika) Tsuku9
(However, their experiments also showed an increase in drag of 3 to 8%.) Very recently, S, W,
Attempted to follow Johnahan and Smith by using Wilkinson beam prets to control rupture by using rectangular repeatlets by using grooved glue prets between the fixation media of the streaks after establishing or creating slow streaks. However, it has not yet been reported whether a net drag reduction was achieved as a result. The results reported from these and other previous studies all indicate that the effectiveness of Ripplet is somewhat limited, thus calling for alternative solutions. U.S. Patent Application No. 686,959 (M, J., Walsh et al. - NASA Case LAR-13286-1) describes a riplet surface with superimposed large eddy current breaking units (LEBU'S) as manipulators for the outer region of the boundary layer. Although it has been proposed to reduce skin layer friction more effectively by providing a skin layer friction, such an arrangement has the disadvantage of considerably increasing complexity and being susceptible to damage due to friction, especially accidents. Another proposal (“On the drag reduction effect of sharkskin”, Benofyat, Hoppe, Rife, AIA
A-85-0546) uses a so-called vortex generator shaped to create a tangential mixing effect using local flow conditions on a ridge pattern structure similar to the shape of scales on sharkskin. It has been suggested that this is appropriate. It has been argued that this can significantly reduce drag, but it is also inherently complex and difficult to simulate scale surfaces that researchers conclude have force due to their low-drag properties. Will. In contrast to these attempts to reduce skin layer friction by somewhat complex means, the riblet surface is less susceptible to damage and can be treated relatively straightforwardly, for example by preforming, e.g. extrusion layer cutting, or by pressing. Alternatively, it can be shaped by applying it. It will be clear that it would be desirable to use such surfaces if they could significantly reduce skin friction drag. The mechanism by which the riplets affect the boundary turbulent layer of wall soil is not yet fully understood. If turbulent flow is close to laminar flow conditions? Even if it can be assumed that the effects of these effects can be assumed, their efficiency should be kept in mind that in the region equivalent to turbulent flow and laminar flow, the skin friction drag in the case of laminar flow is 80 times smaller than that in the case of turbulent flow. is low. What if a significant proportion of this potential improvement could be realized on a replet surface? Its use would provide significant advantages over the drag-reducing composite systems described above. [Akebono point? According to the invention, a series of aerodynamic or hydrodynamic walls extending in the direction of fluid flow relative to a converging surface are used to modify the turbulent boundary layer on the surface. A complete set of long protrusions, the protrusions being a plurality of protrusions of low height, with tall protrusions spaced between each successive pair thereof? What you have prepared will be presented. Are the protrusions a virtually continuous spanwise row? It is desirable to form. Also, a large protrusion with a pointed external shape and a small protrusion? It is also desirable to form them together. The small-height protrusions of the shape according to the invention correspond to the globlets of recent researchers. They serve to ensure that the turbulent eddy movements in the boundary layer penetrate deeply into all parts of the surface, especially into the grooves formed by adjacent replets, so that the turbulent movements cannot be displaced from the walls. Depending on their geometry, they can also suppress the spanker-directed gradient associated with the formation of longitudinal vortices or "streaks" within the boundary 1 - secondary small-scale longitudinal vortices that take energy from the large-scale streaks. It also has some effect on starting the process. However, such replets have hitherto had only limited success. This may be because they had little influence on the vortex development itself and functioned only in a wholly or mainly passive manner. In that case, they are largely incapable of mitigating the vortex-facilitated mixing and momentum transfer, which is a major factor in increasing the boundary layer drag of turbulent flows compared to laminar flows. . However, if, in accordance with the present invention, the large-height protrusions are provided with appropriate spacing between a series of small-height 721J plets or provided as bullets (preferably arranged independently), Longitudinal vortices or streaks moving randomly across the surface can not only be restrained in the direction of lateral forces, but can also be moved separately beyond their natural spacing. By measuring the distance between the spanker scale of the streak and that of the small replet, it is possible to blend these small 7Th I from those streaks into a larger one.
The energy transfer to the small-scale secondary vortices induced by the J-bullets can be promoted faster, and they create an effect that penetrates the area above the small-scale vortices, where they increase the activity of the vortices. Improving the effectiveness of these glue bullets by making them smaller. In this sense, both large and small replets can function with positive force. The shape of the present invention includes at least a protrusion with a large height that is inclined at an angle that changes with respect to the height of the protrusion, and has a mirror surface.
Preferably, each of the side surfaces has an intermediate region of lesser slope than its upper and lower adjacent regions, forming the entire lower portion of the concave profile of the associated protrusion. For best results, the transition to the concave cusp should be established by a projection and positioned at or near the effective height of the fc wall. The region below the transition is a series of V-grooves with substantially planar surfaces and steep sides between the protrusions within their lowest extents? It is desirable that it be formed. As already mentioned, these can perform the action of displacing the turbulent flow m:J from the wall surface. The longitudinal vortices displaced on the effective wall are then controlled by the concave cusps projecting into this region, which by virtue of their different contours exert a strong effect on the vortices. The transition to the concave surface can have a substantially sharp edge, but it is also possible to have a rounded or chamfered fc transition. It is preferable that the concave surface has a relatively sharp edge and a continuous curve at the tip, but they can also be made up of straight and/or curved sections, with the tip itself being flat or rounded for convenience. You can put it on. [Example] The present invention will be described below with reference to the drawings. In Figure 1, the wall surface is ribbed continuously in the span direction in a regular pattern consisting of parallel groups of eight uniform small riblets (r) between individual large replets R, and the ribs are formed by a turbulent boundary layer. Starting from the transition region of the flow on the surface runs in the flow direction on the surface within the region. flow direction

[The extending pattern preferably continues throughout the turbulent boundary layer at the surface. It is not critical that the replets be precisely aligned with the fluid flow; distances ranging from 10 to 15 are permissible. All replets have a triangular outline, but the outline of the pond can also be used, and another outline is 1! Sharp cusps with concave valleys between successive cusps (apexes preferably form an angle of no more than about 20°).
? It is desirable to have one. Furthermore, in Figure 1, the base width is equal to its height, or is it a pret? Although shown, it is desirable to increase the base width to approximately twice the height of each replet. This is particularly true with respect to the cusp profile shown in FIG. The desired dimensions and dimensional relationships of the replets are expressed in dimensionless form in a so-called "wall law" variable in which the actual distance value is multiplied by a "wall units" scalar quantity defined as follows. ν where τ is the wall shear core car p is the fluid density ν is the fluid kinematic viscosity
2, and is similarly set to a pitch S+ of 15 units. R is three times this dimension, has a height of 45 units, width WLk, and a pitch of 3L of 135 units.
f give. Due to the presence of small riblets) r, an effective surface for boundary turbulence of about six quarters of their height above the wall surface itself is established. Therefore, the large replet R
The effective heights of b+, e), i.e. their heights above the effective surface, are approximately 36 units. Larger replets inhibit their random spanwise motion in the area beyond the active surface, increasing their natural spanwise spacing, and also transfer energy from the streaks to small-scale secondary vortices induced by small replets. A streamwise vortex or s) that forms in the boundary layer by promoting the transmission of
It acts to control the long region of J-ri. In this flow mechanism, the action of the two types of ripples is one in which the large ripplets influence the boundary layer and are associated with an inherent reduction in drag, while at the same time creating a flow pattern more suitable for operation by the smaller ripplets. forces, the latter reinforcing each other in that they themselves contribute to the reduction of the skin layer friction by moving the boundary layer turbulence and somewhat above its height. Is the existence of small replets an effective wall part? By varying the wall shear stress, it is possible to reduce the wall shear stress so that the streak becomes weaker and therefore more controllable. Fig. 5 has only one pair of small 721J plates between successive large bullets R, and there is a successive q plate inside it.
Another ripple pattern with IJ prets separated by flat valleys? show. In the case of the special column of FIG. 6, the small replets each have h and S of 15 wall units. The large plets have a height hr, k of 30 units and their pitch S, which is of course the pattern repetition, is 45 units. Particularly when using rounded or flat bottomed valley shapes such as those of FIGS. 2 and 6, it may be desirable to reduce the height of small replets relative to their pitch. In Figure 4, there are seven small ribs between the successive large planes H, h-,5=3.5i units, and hL=i. units, and 5L = 49 units in one row. Many other variations in the size and outline of the replets are possible within the scope of the invention. Preferably, the ratio h:3 is neither less than Fi12 nor greater than 2:1 for small replets. However, for large oriplet, do they have a blade-like outline? A large aspect ratio h:w can be easily tolerated within the given range. As far as dimensions are concerned, the following is a desirable dimension range for a dimensionless wall unit in the case of low-velocity flow. In the case of a small replet r, 2(h (20, but 5(h (45, but 15 (hLe (35
40<240, but 80+130 Generally speaking, the base width WL+ of large plets will be kept smaller than 60 wall units. Variations within the above ranges can be made independently for each parameter, but it goes without saying that the large replets must protrude above the small replets, and a minimum protrusion of the 8-wall single is desirable. Furthermore, S
The relationship to O8+ must always be such that at least two small replets can be inserted between successive large replets. FIG. 5 shows another wall surface riplet pattern within the scope of the present invention in which the profile of the beam plets is completely changed. As in row 1, the small replet r in this example has a dimensionless height h+ of 15 units above the wall and is also set at a pitch S+ of 15 units. The large platelets R have a height of 45 units + ht, and a width WL such that their pitch 3L+ is 135 units. Small 71] Pret) r establishes an effective surface that extends above the wall surface 6+ itself for boundary layer turbulence, and below that level, all of the beam prets are planar inclined sides? have At the level of the effective surface there is a transition t to a small slope, and the replet has a sharp pointed tip from the point of inflection with concave flanks, similar to the concave shape of the replet shown in Figure 2. It continues upwards. At the upper part of the effective wall surface, the thick replet R has a wall height hLe ) of 63, but the corresponding height hLe of the small replet
e) is 6 units. Different contour areas are intended to perform different functions. While the region below the effective wall forms a relatively deep V-groove that can better suppress the penetration of turbulent eddy motion, the concavity beyond the effective wall can absorb energy from large streaks within the boundary layer turbulence. The discharge can be promoted more effectively with a very small-scale longitudinal vortex. Its function?
Is the concave surface a point with a relatively sharp edge to effectively play? should be formed. It will be appreciated that the above-mentioned effects can be achieved, at least substantially, in the case of the deformed sloped sides shown. In particular, for practical reasons, is there an inflection point or cusp on the pret surface? It may be desirable to make it dull. That is, do these surfaces have straight (or even) curved sections on both the bottom and top of the effective wall surface without unduly changing the general character of the external shape required for the above function? You can also prepare. The number of small repeatets between successive large repeatlets can be larger or smaller than the group 8 in the figure, but the outline of the single-car series repeatlets 7) can be varied. If large librenotes only have enough movement to place the IJ-ri in place, their points can be flattened or rounded to reduce their inherent drag without compromising their movement. . however. If they are used to reduce the force of the streaks, the top cusps may be retained and further emphasized by changing the shape to another shape. Similarly,
The external shape of the small replets can be changed according to their function. Performance would be improved if the ripplet at its leading edge was faired into the wall to avoid the drag increments associated with the flow associated with a steep leading edge. Advantages given by beam bullets to reduce wet area gold? It is likewise possible to have a short spanker-extending gap in the machine direction between the bullet regions which is itself larger than the machine direction length of 2δ without sacrificing less than the boundary layer thickness δ. Here we would like to touch on the subject matter of our concurrent patent applications (Case 1-r Control of Boundary Layer Flow and Case 1-R Control of Boundary Layer Flow). Because these other shapes can be used jointly or separately in combination with those of the present patent application (flJ I). Things flJ
[In the case, a reduction in the skin layer friction of the turbulent boundary layer can be obtained by using a series of long protrusions arranged in a repeating pattern towards the spanker, with adjacent protrusions in each pattern projecting to different heights. It will be done. Such a shape can be used with the present invention as shown in FIG. 6, and the group of small height protrusions rl+r2 between successive large protrusions R is more effective in the inner boundary layer region between the large protrusions. Different heights can be given so as to obtain an additional reduction in skin layer friction due to the presence of the large protrusions. This idea is based on the fact that there is a group of adjacent protrusions of uniform height between two protrusions of different heights, and for example, as in the row of FIG. 6, all protrusions r2 are small protrusions r,
The central protrusion can be omitted in the pattern replaced by or can also be realized in a bullet pattern, this last configuration having the advantage of a smaller wetted area. To maintain its effect, the mid-height 17
) Is the U fret eliminated over a span of 50 wall units or more? should be limited to the extent that no group of minimal replets is left. The role of the small protrusions of different heights, as explained in the Other Applications column, is to displace the effective wall surface further than would be possible with protrusions of uniform height. Groups of small protrusions of varying height and alternating large protrusions are as described above.
This is to exercise all the control functions. For that purpose they must extend considerably above the effective wall surface than any of the lower projections. In our case ■, we have two alternating heights of V-groove brackets and a small Z IJ of height h which establishes the effective wall position given the effective height of r2 Pret r. columns are shown. If the effective height of the Libre J Tor2 is in this case called +h4e to distinguish it from the effective height h+,e of the larger Libre Bullet R mentioned earlier in this application, then the new effective wall position H+ is o, 75h, at the height of the area. That is, 0.75(b4e +0.75h)(H((0,
75hIe +0.75h) The effective height above the substantial wall position of the taller replet glues is at least 8 wall units greater, i.e. their height from the first wall surface is)8 + 0.7
5(hle +0.75h). In the case of [Example], a long protrusion is provided on the wall to modify the turbulent boundary layer, and the height is progressive with the distance along the wall in the direction of fluid flow, as shown in Figure 7. Make it bigger. This is true whether they consist of a plurality of low protrusions of uniform height between successive large protrusions, or whether small protrusions are of their own height at any particular station in the flow direction. This can be done for the above protrusion shapes. Although not directly mentioned in the above description, another feature disclosed in our work ① and ② is that different shapes can be incorporated in arbitrary combinations. I want to be understood. For further details on the subject matter of those applications see our Case 11.
You can directly touch the specifications of I. The tip or presto dimension is relatively low free flow velocity (
This seems to be appropriate based on the experimental results conducted on the number (M) of pine trees with U) of about 0.3 or less. However, changes in dimensions, particularly the height of the replets, have been found to be desirable for higher speeds and Matsuha numbers. The machine direction length of the projections would appear to have an important influence on the optimum dimensions, especially for Matsush numbers of about 0.4M and above. Wind barrel tests with a uniform array of single-height V-groove plets with a streamwise length of approximately 1 m give optimal results at high speeds? It is the same pressure of dimensional change by the wall unit that is required to give. The following table gives the total ripple dimensions at the leading edge of the ripplet: 0.1 M) The lower speed results in the range II), 0.4 to 0 in relation to +21
．． These tests 131 with Matsuha numbers in the range of 9M,
Data from +41, +51? This is what is shown. Replet height/span h Is ReL wall unit flll 3 0.8 x 10' 12) 15 3x10' f3N 7 5x 10' (4) 20 10x10'(512515x10' L Ret,'d length Reynolds number = -t LU These results indicate that for optimal results, for an increase in Re+ of 10 times the @edge of the slow riblet compared to the slow riblet at ROL = 1 This indicates that an increase in replet height per wall of approximately 50 cl) is required. That is, for a given free flow velocity, the length of the replet must increase by a factor of 10 and the height of the replet must increase by 504 times. The factors that determine the degree of optimality are many and complex. The underlying body shape with discontinuities and the possibility of non-uniform U-values on the range of riblet rows may further influence the full introduction and empirical evaluation of optimal riblet dimensions may be required. . However, if compensation of ReL can be obtained by increasing the pre-height of the replets and perhaps their spacing - for general purposes with respect to the low velocity values presented in discussing the above sequences - ReL(h+a Re
b) It is suggested that an appropriate scaling factor of the height of the replet in wall units for (b) should be in the range of 1:2Q to 1:B. Similarly, as discussed in detail in Case 1 of our other special application filed at the same time, it is possible to have an increasing full scale of the replet height along the length of the column, regardless of Re L . desirable. [Effects of the Invention] Generally speaking, the present invention can be applied to the wall surface of an airframe where reduction of skin layer friction is required. Therefore, it can provide a full means of reducing drag on the external surfaces of vehicles, including aircraft, land vehicles and seaplanes. It can also be used on machines such as rotating and stationary blades of turbomachines and on the inside surfaces of pipes and conduits. The present invention forms a surface protrusion integrally with the related fuselage, and at the same time creates a necessary surface shape on the upper part of the protrusion. Does this include the possibility of providing a surface member such as a sheet or tape with protrusions that is attached to the fuselage for the purpose of providing a surface material? I want to be understood.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a wall surface perpendicular to the flow direction on a wall surface formed according to the present invention; FIGS.
A series of deformed cross-sectional views that can be applied to the shape shown. r...small replet, R...large replet, 10h...width, W...width, SL...pitch. Engraving of drawings (no changes in content) 51. /66 Procedural amendment (August 7q, 1986) Director General of the Patent Office Kunio Ogawa 1, Case description 2, Name of the invention Hydrodynamic wall 3, Person making the amendment Relationship to the case Applicant address name Name: Rolls ψ Royce PLC 4, Agent Address: Room 206, Room 5, Shin-Otemachi Building, 2-2-1 Otecho, Chiyoda-ku, Tokyo, Date of Amendment Order: July 28, 1988 (Japanese) 3. Subject of correction

Claims (1)

[Claims] 1. A hydrodynamic wall having a series of long protrusions extending in the direction of fluid flow relative to the wall for modifying the turbulent boundary layer above the wall, the protrusions having a plurality of small heights. said wall surface, characterized in that it consists of protrusions of large height spaced between each successive pair of protrusions. 2. A wall according to claim 1, wherein the projections form a substantially continuous spanwise row. 3. Claim 1, characterized in that the protrusion extends in the flow direction over at least the length of the turbulent boundary layer region.
Wall surfaces described in Items 1 to 2. 4. The wall surface according to any one of claims 1 to 4, wherein the small protrusion and/or the large protrusion have a sharp pointed shape. 5. The wall surface according to any one of claims 1 to 4, which has a protruding outer shape. 6. The wall surface according to any one of claims 1 to 4, wherein the protrusion has a concavely curved valley between the cusps. 7. Wall surface according to any one of claims 1 to 6, characterized in that flat-bottomed valleys are provided between at least some of the projections. 8. A wall according to any one of claims 1 to 7, characterized in that the larger projections have an effective height that is at least 8 units greater than the smaller projections. 9. The wall surface according to any one of claims 1 to 8, characterized in that there are at least two small protrusions of different heights between the successive large protrusions. 10. The wall surface according to any one of claims 1 to 9, wherein the height of the protrusion increases in the flow direction. 11. At least the projection having a large height has side surfaces that slope at an angle that varies depending on the height of the projection, and each of the side surfaces has an intermediate region having a slope smaller than that of the adjacent regions above and below the associated projection. 11. A wall surface according to any one of claims 1 to 10, characterized in that it forms the lower part of a concave point. 12. Claim 11 characterized in that all projections extending beyond the effective height of the wall have side walls of varying slope such that the intermediate region is positioned approximately at the effective height of the wall.
The wall surface described in section. 13. Claims 1 to 12, characterized in that there is at least one gap between the lengths of the protrusions, and the width of the gap is not larger than half the length of the adjacent protrusions. The wall surface described in.