INTERIOR FLOW SIMULATION OF SUCTION CHAMBERS FOR HLFC PROFILES

Transcription

1 DocumentID: INTERIOR FLOW SIMULATION OF SUCTION CHAMBERS FOR HLFC PROFILES H. Lüdeke, DLR, Intitut für Aerodynamik und Strömungtechnik, Lilienthalplatz 7, Braunchweig, Germany Abtract For a implified but effective uction chamber concept for hybrid laminar flow control by boundary-layer uction, which i invetigated on a vertical tail, the velocity ditribution inide uction chamber i imulated. Within the current tudy, CFD imulation of the flow inide thee chamber are carried out by the DLR FLOWer code to predict thi velocity a well a the preure ditribution inide the chamber. Variation of the uction preure and the tap-ditance are carried out. 1. INTRODUCTION Within different EU-project, hybrid laminar flow technology with uction through a porou leading edge of a vertical tail plane (VTP) i invetigated by windtunnel tet and numerical analyi by computational fluid dynamic. The aement for the integration of an HLFC ytem into a long range aircraft ha to anwer the following two quetion: How doe the integration of an HLFC ytem into a given long range a/c configuration influence aircraft performance? What i the optimal HLFC aerodynamic and ytem configuration to obtain maximum performance benefit? Principal feaibility of HLFC for large tranport aircraft wa hown for example by Airbu with the fight tet of an HLFC ytem on the vertical tail plane of an A320 aircraft [1],[2]. The uction ytem for thee tet were deigned to explore the limit of HLFC and were rather complex to explore the envelope of applicability of HLFC. After having hown that HLFC doe deliver the aerodynamic reult, impler and lighter ytem were developed to obtain the overall benefit for the aircraft. A major tep wa the implified uction ytem developed within the European ALTTA project [3]. Thi ytem work without the complex tructure of claical ytem [4][5] and i currently being refined within the German national project VER²SUS. A numerical invetigation of the uction on the boundary layer i carried out in [6]. The concept of an outer porou urface with a ubtructure of tringer and a econd inner heet provide a double-wall hell with a number of integrated uction chamber (FIGURE 1). Inide of thee uction chamber given circular orifice allow the choice of an individual preure to extract enough material and to generate a boundary layer with maximum laminar range. For thee chamber the quetion of contant uction velocitie along the outer heet i crucial, while the flow-field inide thee chamber wa not invetigated in detail up to now. Within the cope of thi paper the flow inide thee chamber i imulated under implified aumption. The idealization of the geometry allow two dimenional calculation in cut though the center plane of the chamber between two repective tap while the ret of the flow i expected periodically repeated (FIGURE 1). The Tap are replaced by lot of the ame urface to provide a contant given ma-flow. In the middle between two lot another ymmetry plane can be et due to the identical flow in each direction. The uction through the outer heet i modeled under the aumption of an analytical quadratic relation between preure-difference over the porou wall and the uction velocity a determined within the ALTTA project [3]. The preure outide the wall i determined from former calculation and kept contant. Finally the duct inide the orifice i added by the ue of a precribed-preure boundary condition. Afterward the velocity ditribution along the porou wall inide the chamber a well a the preure ditribution i calculated. Different configuration of chamber and tap-ditance are imulated by invicid a well a Navier-Stoke imulation. Suction-Chamber Duct Porou outide heet Orifice inner heet FIGURE 1. Overview of the uction-panel geometry. The ketch of the A320 tail i taken from [3]. 1

2 Spanwie direction FIGURE 2. Idealization of the circular tap in a panwie row by lot of identical urface. 2. CONFIGURATION 2.1. Geometry Orifice Identical urface Inner panel heet 2D-lot The concept of an outer porou urface with a ubtructure of tringer and a econd inner heet provide a double-wall hell with a number of integrated uction chamber (FIGURE 1). Inide of the uction chamber drilled circular orifice allow the choice of an individual preure to extract enough material and to generate a boundary layer on the wing-urface with maximum delay of laminar-turbulent tranition. For thi tudy the inner geometry i expected a a rectangular pace without any curvature which i nearly infinitely long in panwie direction. By thee aumption two-dimenional imulation on very imple CFD-grid are poible. In the following, implification will be decribed, that allow 2D calculation between two repective orifice, while the flow i expected perfectly periodic in panwie direction Idealization Variou idealization of the complex flow field a well a the geometry are carried out. The uction velocity i determined by the local preure lo over the porou heet only, omitting any influence of ingle microporoitie. The urface preure at the boundary-layer wall i taken from the imulation of the tail profile and i et a a contant in time and pace. To replace the inherently 3D flow by a 2D approximation the circular orifice are replaced by lot of the ame urface a the uction hole (FIGURE 2). Thi implification will provide the ame material flow a the orifice but can be imulated by a 2D cut through the chamber-centerline (FIGURE 3). After thi implification, the flow between two lot i expected periodic and ymmetric and two ymmetry plane are defined: one in the middle between lot and the other jut in the middle of the next lot The duct on the inner ide of the orifice i replaced by a coare farfield-grid with a given exit-preure, which i provided by the fraction of outer and duct-preure. Finally a rectangular domain i calculated between one orifice and the next ymmetry plane in panwie direction and the porou wall, the duct wall and the duct-farfield in wall-normal direction. The flow-field i expected a an infinitely repeated tructure all over the panwie dimenion which i jutified by the chamber ize of 2m. FIGURE 3. Left: top-view of the uction-panel with lot. Right: ide-view of the panel with lot and ymmetry plane Geometric data The chamber have generally a rectangular hape with a wall-normal dimenion of 10mm, an average chordwie diameter of 100mm and a panwie length of 2m. Circular orifice with diameter of 3mm are located in a row on the duct-wall (FIGURE 1) along thee 2 meter at a ditance between 0.125m and 0.25m. So a maximum of 16 equiditant tap appear for each chamber. FIGURE 4. Definition of the grid in the duct behind the uction panel CFD grid Uing the formally defined implification, a rectangular CFD grid i generated by taking into account trong velocity gradient at the uction lot, near the porou wall, and inide the duct. The Euler meh i refined near the porou wall to reolve the gradient from the uction velocitie. 2

3 Navier toke grid are extenively refined with repect to all wall to reolve the boundary-layer gradient. Approximately 18 cell are located inide the lot (halfdiameter) while 110 cell define the duct-wall. The uction chamber contain 48 cell wall-normal and the Ductfarfield i reolved with 24 cell (FIGURE 5). The calculation require up to 8 order of magnitude convergence before a teady flow inide the chamber i reached, imilar convergence i required for the duct. Cae No.: P External [Pa] P Duct [Pa] L Domain [m] Cae Cae Cae TAB 1. Flow condition and geometry for three different cae. FIGURE 5. Suction panel grid and grid-detail in the lot region Flow condition The flow though the uction chamber i defined by the boundary condition, The Mach-number outide the porou wall and the preure at the porou wall a well a the pre-cribed duct-preure. While the preure outide the porou wall i choen a a reference value, the duct preure i given by a ratio between both preure-value. To chooe a given external preure for the uction wall of Pa and a duct-preure of 99250Pa, the ratio for the code i approx The reference Mach number of i valid outide the porou wall, while inide the duct very mall Machnumber within a range of 0.01 appear. Even inide the duct very mall flow velocitie are invetigated. A a firt tep, invicid imulation are carried out with lip-wall for the chamber a well a for the duct. For vicou imulation a reference Reynold-number per meter of 7 Million i choen. Due to the very mall velocitie inide the chamber, the Reynold-number per meter i about 1400 in the region of interet. Three Tet-cae at different Preure-value and orificeditance are defined to provide a mall overview of the influence of thoe parameter (TAB 1). The relation between uction velocity and preure difference i taken from the ALTTA experiment and will be decribed in detail in the next chapter. 3. CODE DESCRIPTION All calculation in thi paper were carried out with the DLR FLOWer code [7] by olving the compreible Reynoldaveraged Navier Stoke equation on block-tructured grid with econd order finite volume technique and cellcentered variable. Time advancement i applied by a five-tep low-torage econd order Runge Kutta method. Turbulence i modeled by either algebraic or tranport equation model. The code i adapted to the imulation of exterior flow field around complex configuration. Since a rotating reference frame can be ued. The numerical procedure i baed on tructured mehe, uing a central cell-vertex or cell-centered finite volume formulation. Diipative term are explicitly added in order to damp high frequency ocillation and to allow ufficiently harp reolution of hock wave in compreible flow. On mooth mehe, the cheme i econd order accurate in pace. Time integration i carried out by an explicit hybrid multitage Runge-Kutta cheme. For teady tate calculation the integration i accelerated by the technique of local time tepping, enthalpy damping for invicid flow and implicit reidual moothing. The olution procedure i embedded into a ophiticated multigrid algorithm which allow tandard ingle grid computation a well a ucceive grid refinement, with the option of imple or full multigrid. The code i written in a flexible block tructured form enabling treatment of complex aerodynamic configuration with any meh topology. Two dummy layer around each block are choen in order to maintain the econd order accuracy in pace at block interection. FIGURE 6. Relation of preure drop and uction velocity acro micro-perforated kin: the ALTTA curve. 3

4 3.1. Porou-wall boundary condition The relation between uction velocity and preure difference i taken from the ALTTA curve (FIGURE 6) where the following empirical formula wa found to connect uction-velocity and difference-preure over the micro-porou wall: p c = A μ μ 0 w + B ρ ρ 0 w 2 Where the uction preure i p c, and w i the uctionvelocity at the wall. Due to a very mall preure-difference and uctionvelocity ( p c < 600 Pa, w < 0.03 m/) the non-linear part B i omitted. For the ame reaon μ μ 0 i expected, o a linearized relation of uction velocity and preure difference i finally ued: p c = A w Were A i the lope of the ALTTA-curve (at H=0) near zero-preure. The dimenional value i calculated from the ecant between 0 m and 0.03 m by A = Pa. m Tet-calculation at = Pa, which i the lope of the m curve at 0 m, have hown minor difference in the global tendency. Neverthele the value of Pa hould be m more accurate and i conequently choen in the following. ditance between the orifice of m (top picture of FIGURE 7). The reulting preure-ditribution in the uction-chamber and the uction-velocity along the wall i hown in FIGURE 7. The preure-variation along the porou wall i nearly contant between Pa and Pa, a variation of le than 0.03%. The uction-velocity of about m/ varie in the ame range for thi tet-cae, which i equivalent with v uction 4 μm. cae 1 4. RESULTS For the choen realitic ditance of the orifice, homogeneouly mall uction velocitie are calculated along the porou wall. Variation are hown for different duct preure and different tap-ditance. For all invicid calculation, the variation of the preure inide the chamber i le than 0.08% related to the average chamber preure Invicid imulation The geometrical data a well a the flow condition are taken from the experiment within the cope of the VER²SUS experiment. In the following, reult for the three choen geometrie and preure-ratio (ee TAB 1) are preented. The fact of nearly zero velocitie inide the chamber ha to be pointed out, o the treamline in the calculated flow-field don t repreent vortice in the claical ene, but tructure in a very lowly moving fluid. Due to thee extremely mall velocitie in the chamber, and the approximately 100 time maller value inide the duct, viibly cloed treamline won t be called recirculation-region or vortice but flow-tructure in the following. cae 2 cae Cae1 The external preure for thi tet-cae i choen by Pa at a Duct preure of Pa and a FIGURE 7. Velocity ditribution along porou panel wall and preure inide the chamber. 4

5 Such a tructure of cloed tream-line appear inide the chamber between ymmetry-plane and uction-lot due to the lip-wall condition that allow tangential velocity component along the porou wall. Thi tructure i reponible for the velocity-maximum at the wall coordinate -0.11m Cae 2 For the econd tet-cae the external preure i reduced to Pa at a duct preure of Pa. The ditance between the orifice i again 0.25 m with the ame lotdiameter (middle picture of FIGURE 7). Cloed tream-line appear in the chamber a well, but the region of thi tructure i ignificantly reduced which i a reult of the larger preure-ratio between duct and porou-wall preure. No local maximum of the uction velocity i viible in contrat to cae 1. p inide the chamber i nearly contant in a range between Pa and Pa which i a lightly larger dimenional difference than in cae 1 while the relative variation i kept imilar below value of 0.03% due to the increaed average preure Cae 3 Thi i a variation of the orifice-period. The number of lot i doubled and conequently the domain-ize i cut into halve. External and duct preure are the ame a in cae 2, the lot-ize i fitted to the contant hole-diameter of 3mm. Since the geometry of the chamber fit better to the flow inide, cloed treamline do not appear any more, and the uction velocity how no maximum apart from the uction lot. A very mall region with cloed tream-line i viible in the top-left corner of the chamber. Thee little flow-tructure appear alo in cae 2. Another outcome of the doubled orifice-number i the preure difference in the chamber which i nearly doubled in comparion with cae 2. It i found in a range between Pa and Pa. The relative variation i even maller than in cae 2: about 0.02% Navier-Stoke imulation A vicou calculation for cae 2, which i a good repreentation of the foreeen experiment, i demontrated in thi ection. A refined grid for the non-lip boundary condition i generated to reolve the boundarylayer and the flow through the uction lot. For a nominal unit Reynold-number of /m, the imulation have hown imilar mall velocitie inide the chamber a already demontrated for the invicid cae. The flow between the inner wall of the chamber conequently get a very mall repreentative unit Renumber of about /m. For thi reaon only laminar flow i expected inide the chamber. Chamber- a well a duct wall are defined by non-lip boundary condition, though the boundary-layer influence in the duct i expected to be negligible. Numerically, convergence over more than 8 order of magnitude i neceary until the final flow-field i etablihed. Due to the trong gradient near the uction lot and the very mall preure and velocity variation at the porou wall, thi i not an unexpected reult if the reduced time-tep for the mall near-wall cell of the refined grid are kept in mind. The vanihing tangential velocity-component at the porou wall reult in perpendicular treamline at thi boundarylayer edge, dominated by the uction-velocitie. For thi reaon no more cloed treamline appear in the chamber and each part of the flow i directed toward the lot without any detour. Comparable preure- and velocity ditribution a in the invicid cae 2 are predicted by thi calculation. Even velocitie in the lot region are in the ame range. FIGURE 8. Velocity ditribution along porou panel wall and difference preure inide the chamber by a Navier-Stoke imulation of cae CONCLUSION For a implified uction chamber concept for hybrid laminar flow control by boundary-layer uction, the 2D flowfield inide the chamber i imulated. Within the current tudy, CFD imulation of the flow inide different geometrie are carried out by the DLR FLOWer code to predict velocity a well a preure ditribution behind the porou heet. Variation of the uction preure and the tap-ditance are carried out for invicid a well a vicou flow. The uction through the micro-porou urface i approximated by a flux boundary condition, uing an analytic relation between difference-preure and uction velocity at the wall. The reult how very mall variation of the relevant flow data like uction velocity and chamber preure. Both are nearly contant for the invetigated geometrie by imulating invicid a well a vicou flow, while the tructure of the flow-field inide the chamber change if non-lip wall and an invicid approach are ued. Variation of the difference between external and duct preure have hown other mean data but very little change in the variation behavior. Thi tatement hold for a doubling of the orifice along the panwie direction. While the reult indicate, that the velocity-ditribution at the uction-wall can be optimized by adjuting the ductpreure or the number of orifice, no extenive neceity for uch an improvement i technically given. 5

6 [1] R.D. Jolin: Overview of laminar flow control. NASA/TP [2] R. Henke: A320 HLF fin flight tet completed. Air&Space Europe, 1, pp [3] G. Schrauf, K.H. Hortmann: Simplified hybrid laminar flow control. ECCOMAS 2004, Jyväkylä, Finland, July CD-Proceeding [4] C.-H. Rohardt, A. Seitz, et.al.: Simplified-HLFC/ Entwurf eine Seitenleitwerk mit Hybrid- Laminarhaltung für den Airbu A320. Deutcher Luftund Raumfahrt Kongre, , Bremen. [5] K.-H. Hortmann, W. Schröder: Simplified Suction Sytem for a HLFC L/E Box of an A320 Fin. ALTTA Technical Report TR 23, [6] S. Enk: Invetigation of Boundary Condition for the Simulation of Suction by Hybrid Laminar Flow. Deutcher Luft- und Raumfahrt Kongre, , Stuttgart. [7] N. Kroll, C.C. Roow, D. Schwamborn, K. Becker and K. Heller: Megaflow a Numerical Flow Simulation Tool for Tranport Aircraft Deign. ICAS 2002 Congre,