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Kenneth W. Iliff - One of the best experts on this subject based on the ideXlab platform.

  • in flight subsonic lift and Drag characteristics unique to blunt Based lifting reentry vehicles
    Journal of Spacecraft and Rockets, 2007
    Co-Authors: Edwin J Saltzman, Charles K Wang, Kenneth W. Iliff
    Abstract:

    Lift and Drag measurements have been analyzed for subsonic flight conditions for seven blunt-Based reentry-type vehicles. Five of the vehicles are lifting bodies (M2-F1, M2-F2, HL-10, X-24A, and X-24B) and two are wing-body configurations (the X-15 and the Space Shuttle Enterprise). Base pressure measurements indicate that the Base Drag for full-scale vehicles is approximately three times greater than predicted by Hoerner's equation for three-dimensional bodies. Base Drag and forebody Drag combine to provide an optimal overall minimum Drag (a Drag "bucket") for a given configuration. The magnitude of this optimal Drag, as well as the associated forebody Drag, is dependent on the ratio of Base area to vehicle wetted area. Counter-intuitively, the flight-determined optimal minimum Drag does not occur at the point of minimum forebody Drag, but at a higher forebody Drag value. It was also found that the chosen definition for reference area for lift parameters should include the projection of planform area ahead of the wing trailing edge (i.e., forebody plus wing). Results are assembled collectively to provide a greater understanding of this class of vehicles than would occur by considering them individually.

  • aerodynamic assessment of flight determined subsonic lift and Drag characteristics of seven lifting body and wing body reentry vehicle configurations
    2002
    Co-Authors: Edwin J Saltzman, Charles K Wang, Kenneth W. Iliff
    Abstract:

    This report examines subsonic flight-measured lift and Drag characteristics of seven lifting-body and wing-body reentry vehicle configurations with truncated Bases. The seven vehicles are the full-scale M2-F1, M2-F2, HL-10, X-24A, X-24B, and X-15 vehicles and the Space Shuttle Enterprise. Subsonic flight lift and Drag data of the various vehicles are assembled under aerodynamic performance parameters and presented in several analytical and graphical formats. These formats are intended to unify the data and allow a greater understanding than individually studying the vehicles allows. Lift-curve slope data are studied with respect to aspect ratio and related to generic wind-tunnel model data and to theory for low-aspect-ratio platforms. The definition of reference area is critical for understanding and comparing the lift data. The Drag components studied include minimum Drag coefficient, lift-related Drag, maximum lift-to Drag ratio, and, where available, Base pressure coefficients. The influence of forebody Drag on afterbody and Base Drag at low lift is shown to be related to Hoerner's compilation for body, airfoil, nacelle, and canopy Drag. This feature may result in a reduced need of surface smoothness for vehicles with a large ratio of Base area to wetted area. These analyses are intended to provide a useful analytical framework with which to compare and evaluate new vehicle configurations of the same generic family.

  • flight determined subsonic lift and Drag characteristics of seven lifting body and wing body reentry vehicle configurations with truncated Bases
    37th Aerospace Sciences Meeting and Exhibit, 1999
    Co-Authors: Edwin J Saltzman, Charles K Wang, Kenneth W. Iliff
    Abstract:

    This paper examines flight-measured subsonic lift and Drag characteristics of seven lifting-body and wing-body reentry vehicle configurations with truncated Bases. The seven vehicles are the full-scale M2-F1, M2-F2, HL-10, X-24A, X-24B, and X-15 vehicles and the Space Shuttle prototype. Lift and Drag data of the various vehicles are assembled under aerodynamic performance parameters and presented in several analytical and graphical formats. These formats unify the data and allow a greater understanding than studying the vehicles individually allows. Lift-curve slope data are studied with respect to aspect ratio and related to generic wind-tunnel model data and to theory for low-aspect-ratio planforms. The proper definition of reference area was critical for understanding and comparing the lift data. The Drag components studied include minimum Drag coefficient, lift-related Drag, maximum lift-to-Drag ratio, and, where available, Base pressure coefficients. The effects of fineness ratio on forebody Drag were also considered. The influence of forebody Drag on afterbody (Base) Drag at low lift is shown to be related to Hoerner's compilation for body, airfoil, nacelle, and canopy Drag. These analyses are intended to provide a useful analytical framework with which to compare and evaluate new vehicle configurations of the same generic family.

Khan, Sher Afghan - One of the best experts on this subject based on the ideXlab platform.

  • Machine learning applications in modelling and analysis of Base pressure in suddenly, expanded flows
    'MDPI AG', 2021
    Co-Authors: Jaimon, Dennis Quadros, Khan, Sher Afghan, Aabid Abdul, Alam, Mohammad Shohag, Baig Muneer
    Abstract:

    Base pressure becomes a decisive factor in governing the Base Drag of aerodynamic vehicles. While several experimental and numerical methods have already been used for Base pressure analysis in suddenly expanded flows, their implementation is time‐consuming. Therefore, we must develop a progressive approach to determine Base pressure (β). Furthermore, a direct consideration of the influence of flow and geometric parameters cannot be studied by using these methods. This study develops a platform for data‐driven analysis of Base pressure (β) prediction in suddenly expanded flows, in which the influence of flow and geometric parameters including Mach number (M), nozzle pressure ratio (η), area ratio (α), and length to diameter ratio (φ) have been studied. Three different machine learning (ML) models, namely, artificial neural networks (ANN), support vector machine (SVM), and random forest (RF), have been trained using a large amount of data developed from response equations. The response equations for Base pressure (β) were created using the response surface methodology (RSM) approach. The predicted results are compared with the experimental results to validate the proposed platform. The results obtained from this work can be applied in the right way to maximize Base pressure in rockets and missiles to minimize Base Drag

  • Benefit of Mach number and expansion level on the flow development in a cylindrical tube diameter of 18 mm
    Elsevier Ltd, 2021
    Co-Authors: Khan, Sher Afghan, Baig, Maughal Ahmed Ali, Ridwan R, Rayid Muneer, Suheel J, Faheem Mohammed
    Abstract:

    In this paper, experiments are performed at high Mach numbers to examine the flow control effect located in the separated region at 6.5 mm from the central jet. A circular orifice is placed in the wake region to manipulate the Base flow to boost the wake area’s pressure and ultimately reduce the Base Drag. The study also investigates the impact of micro-jets on the stream of the tube. Accordingly, tests are conducted using C-D nozzles fabricated at Mach 1.87, 2.2, and 2.58. Flow generated from these nozzles is exhausted in a duct whose diameter is 18 mm. The results show that for duct length 6D and above, the flow field inside the duct becomes oscillatory, whereas such fluctuations are not noticed when duct size is less than 4D. Dynamic control shows mixed trends when jets are operating at design NPR or under the impact of favorable pressure. And within reattachment length, active flow control is not able to impact the flow pattern. When nozzles are running underneath, over-expansion and flow control are initiated; it decreases the duct’s pressure. The smallest duct size essential for the stream to continue connected appears to be 1D for Mach 1.87 and Mach 2.2 and 2.58; this requirement is 2D

  • Enlarge duct length optimization for suddenly expanded flows
    'Techno-Press', 2020
    Co-Authors: Pathan, Khizer Ahmed, Dabeer, Prakash S, Khan, Sher Afghan
    Abstract:

    In many applications like the aircraft or the rockets/ missiles, the flow from a nozzle needs to be expanded suddenly in an enlarged duct of larger diameter. The enlarged duct is provided after the nozzle to maximize the thrust created by the flow from the nozzle. When the fluid is suddenly expanded in an enlarged duct, the Base pressure is generally lower than the atmospheric pressure, which results in Base Drag. The objective of this research work is to optimize the length to diameter (L/D) ratio of the enlarged duct using the CFD analysis in the flow field from the supersonic nozzle. The flow from the nozzle drained in an enlarged duct, the thrust, and the Base pressure are studied. The Mach numbers for the study were 1.5, 2.0, and 2.5. The nozzle pressure ratios (NPR) of the study were 2, 5, and 8. The L/D ratios of the study were 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Based on the results, it is concluded that the L/D ratio should be increased to an optimum value to reattach the flow to an enlarged duct and to increase the thrust. The supersonic suddenly expanded flow field is wave dominant, and the results cannot be generalized. The optimized L/D ratios for various combinations of flow and geometrical parameters are given in the conclusion section

  • An investigation of effect of control jets location and blowing pressure ratio to control Base pressure in suddenly expanded flows
    'Journal of Thermal Engineering', 2020
    Co-Authors: Pathan, Khizar Ahmed, Dabeer, Prakash S, Khan, Sher Afghan
    Abstract:

    The Drag force is an essential factor in any projectile from road vehicles to rocket or aircraft. The total Drag includes skin friction Drag, wave Drag, and Base Drag. The Base Drag is the Drag due to low pressure in the Base region of the projectile. In the case of suddenly expanded flows, due to the sudden expansion of flow from the nozzle into the enlarged duct, the low pressure is created in the Base region of the enlarged tube, which results in Base Drag and hence overall thrust reduced. In this paper Computational Fluid Dynamic (CFD) analysis is used to analyze the effect of secondary air blowing jets called control jets to control Base pressure in the Base region of the suddenly enlarged duct. These control jets are placed at different Pitch Circle Diameters (PCD) on the Base face of the enlarged pipe. The objective of this work is to increase the Base pressure up to atmospheric pressure and hence reduces the Base Drag. Mach number 3.0 is considered for analysis. The CFD analysis is done for different combinations of Area Ratios (AR) (2, 5 and 8), Nozzle Pressure Ratios (NPR ) (2, 5 and 8) and PCD (d 1, d 2, and d3. Further analysis is done for different air blowing pressure ratios (BPR) to optimize air blowing pressure. The analysis results are plotted for different area ratios, nozzle pressure ratios, and PCD of control jets. By observing results, it can be concluded that the Base pressure is strongly influenced by AR, NPR, and PCD of control jets. The air blowing pressure should be optimum to save energy, and the optimum values can be selected from the results

  • Base and wall pressure control using cavities and ribs in suddenly expanded flows -an overview
    Penerbit Akademia Baru, 2020
    Co-Authors: Sethuraman Vigneshvaran, Rajendaran Parvathy, Khan, Sher Afghan
    Abstract:

    An understanding of fluid flow in sudden expansion has resulted in a great deal of research work in this area. Of particular interest is the study of Base Drag which influences the performance of automotive vehicles, aircraft, and missiles. Problems of fuel mixing in combustion chambers and reduction of specific fuel consumption are also governed by the phenomenon of Base Drag. It is the aim of this study to present a brief review of the work carried out in the area of sudden expansion in a duct with particular accent on a few active and passive controls employed to modify the Base Drag. It is noteworthy that a reduction in Base Drag is of benefit in combustion mechanisms while an in-crease in Base Drag is preferred for net Drag reduction of bodies moving through air. Suppression of flow oscillations that accompany the control of Base Drag also merits attention. A few suggestions by way of future work are also discussed

Maria Vittoria Salvetti - One of the best experts on this subject based on the ideXlab platform.

  • connection between Base Drag separating boundary layer characteristics and wake mean recirculation length of an axisymmetric blunt Based body
    Journal of Fluids and Structures, 2015
    Co-Authors: Alessandro Mariotti, Guido Buresti, Maria Vittoria Salvetti
    Abstract:

    Abstract The variation of the Base Drag of an axisymmetric bluff body caused by modifications of the boundary-layer separating at the sharp-edged contour of its Base is analysed through different numerical simulations, and the results are compared with those of a previous experimental investigation. Variational MultiScale Large-Eddy Simulations (VMS-LES) are first carried out on the same nominal geometry and at the same Reynolds number of the experiments. Subsequently, Direct Numerical Simulations (DNS) are performed at Reynolds numbers that are roughly two orders of magnitude lower, in order to investigate on the sensitivity of the main findings to the Reynolds number. The results of experiments, VMS-LES and DNS simulations show that an increase of the Base pressure – and thus a decrease of the Base Drag – may be obtained by increasing the boundary layer thickness before separation, which causes a proportional increase of the length of the mean recirculation region behind the body. In spite of the different setups, Reynolds numbers and turbulence levels in the experiments and numerical simulations, in all cases the Base pressure is found to be directly proportional to the length of the mean recirculation region, which is thus a key index of the Base Drag value. In turn, the recirculation length seems to be connected with the location of the incipient instability of the detaching shear layers, which can be moved downstream by an increase of the thickness of the separating boundary layer and upstream by an increase of the turbulence level.

Xiaolei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • pool fire flame Base Drag behavior with cross flow in a sub atmospheric pressure
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Xiaolei Zhang, Michael A Delichatsios, Chen Kuang
    Abstract:

    Abstract This paper investigates the effect of cross flow of air on flame Base Drag in pool fires in sub-atmospheric pressure, where no data is available, by combining the effects of these two factors: sub-atmospheric pressure and cross flow. Experiments were carried out using heptane and acetone as fuels for 10–25 cm square pool fires where the cross flow was provided by a wind tunnel built in Lhasa city-Tibet (64 kPa) as well as correspondingly by a wind tunnel in Hefei city (100 kPa). Additional larger scale experiments were also conducted with 45 cm, 60 cm and 70 cm square pool fires in Hefei city. The evolution of flame Base Drag length as a function of cross flow air speed was quantified. The flame Base Drag length was found to be larger in the sub-atmospheric pressure than that in normal pressure, indicating higher risk of causing fire spread to nearby fuel at the ground level. Previous correlations Based on a wind Froude number are not in agreement with each other. In addition, they do not include all the physics and they do not account for the effect of the pressure change on flame Base Drag length. A new theoretical approach is proposed accounting for the relation of wind force with the buoyancy of the flame and the interaction of wind with the total heat release rate from the fire. It follows that three independent dimensionless quantities are introduced: the (inverse) fire source Froude number owing to flame buoyancy, the total buoyancy–wind interaction number and the ratio of fuel vapor density near the fuel surface to the air density. This theory allows us to develop and validate a correlation for flame Base Drag length to account for pressure effect and for generalizing the existing relations for flame Base Drag.

  • flame Base Drag of pool fires with different side wall height in cross flows a laboratory scale experimental study and a new correlation
    Fuel, 2016
    Co-Authors: Xiaozheng Zhang, Xiaolei Zhang, Cheng Kuang
    Abstract:

    Abstract This paper investigates the effect of pool side wall height on flame Base Drag behavior of pool fires in cross flow of air, which has not been quantified in the literatures. Laboratory-scale experiments are carried out to measure the flame Base Drag lengths of pool fires using gaseous square quartz sand box as burner of different sizes (10 cm, 15 cm and 20 cm), employing propane as fuel with pool side wall heights of 2 cm, 3 cm, 4 cm and 5 cm above the ground. It is found that flame Base Drag length is smaller when the pool side wall is higher and increases with increase in fuel supply rate or cross flow air speed, meanwhile decreases with increase in pool size. A new formula is proposed to interpret the evolution behavior that the flame Base Drag length in relation to these quantities, Based on the interaction of cross flow to the buoyancy of the fire. The proposed formula is shown to well correlate the data of different pool sizes and side wall heights non-dimensionally by Froude number, dimensionless heat release rate and the density ratio between the fuel and air.

Pr Viswanath - One of the best experts on this subject based on the ideXlab platform.

  • Drag reduction from square Base afterbodies at high speeds
    Journal of Aircraft, 2004
    Co-Authors: N B Mathur, Pr Viswanath
    Abstract:

    Experiments have been carried out in the 0.5-m Base flow wind tunnel at high speeds evaluating the Drag reduction potential of a family of square Base afterbodies including jet flow at the Base. Direct afterbody total Drag measurements have been made on square Bases as well as conventional axisymmetric afterbodies with conical and circular arc boat tails having the same annular Base area and jet flow parameters. The results show conclusively that, in the Mach-number range of 0.95‐1.60, the square-Base afterbodies have globally minimum Drag in the range of jet pressure ratio studied; the total Drag reduction observed is about 10‐12% relative to the circular arc afterbodies, which can be of significant value in design applications. Certain broad flow features on square-Base afterbodies are discussed Based on surface-pressure measurements and surface flow-visualization studies. Nomenclature Ab = annular Base area Ab/A f = ratio of annular Base area to forebody area, 0.23 A f = forebody cross-sectional area A j = area of jet at exit A j/A f = ratio of jet exit area to forebody area, 0.30 C D = afterbody total Drag coefficient; Drag force/(q∞∗ A f ) CDb = Base-Drag coefficient; Base force/(q∞∗ A f ) C Dβ = boat-tail profile Drag coefficient; boat-tail Drag force/(q∞∗ A f ) C p = afterbody surface-pressure coefficient; ( p − p∞)/(0.5γ p∞ M 2 ∞ ) Cpb = Base-pressure coefficient; ( pb − p∞)/(0.5γ p∞ M 2 ∞) D = forebody diameter of the model, 127 mm db = Base diameter d j = nozzle-exit diameter M∞ = freestream Mach number Poj/ p∞ = jet pressure ratio; ratio of stagnation pressure of jet to the freestream static pressure pb = Base pressure p∞ = freestream static pressure q∞ = dynamic pressure (0.5γ p∞ M 2 ∞) β = boat-tail angle, see Fig. 3

  • Base Drag reduction caused by riblets on a gaw 2 airfoil
    Journal of Aircraft, 1998
    Co-Authors: Channa Raju, Pr Viswanath
    Abstract:

    AMONG various methods explored for turbulent Drag reduction on aerodynamic surfaces, riblets have beer the most promising.' As much as 4-8% of viscous Drag reduction has been reported for simple two-dimensional configurations Plastic sheets with symmetric v-grooves (manufactured by the 3M Co.) have been employed widely in research- Assessment of viscous Drag reduction on two-dimensional airfoils. both at low and transonic speeds, has been reported as well.- Excellent reviews on the subject covering aspects of Drag reduction and flow structure are contained in Refs. 1 and 7. 13; There have been very few attempts exploring the fuse of giblets in separated flows, either from the point of view of Drag reduction or separation control-r'xB0; Recently. Krishnan et al.' showed that riblets actually increase the Base Drag (about 8.7 on a long axisymmetric body with a blunt Base at low speeds: the Base diameter was about four times the boundary -layer thickness ahead of the Base corner-They used 3M riblet sheers and systematically studied the effect of h+` on Base pressure. They also speculated that, while riblets caused an increase in the Base Drag for a large-scale separated flow (like on the axisymmetric blunt Base'), the effect could be favorable on an airfoil with a blunt trading edge, which is a case of a small-scale separated flow. 13; The present investigation was undertaken specifically to assess the effect of 3M riblets on the Base pressure of an airfoil with a blunt trailing edge. Experiments were made at low speeds on a 13.6% thick GAW(2) airfoil model, which has a trailing-edge thickness ratio of 0.5%. The results show very clearly that the Base Drag reduction of an engineering value can be achieved for the optimized riblet geometry.

  • flow management techniques for Base and afterbody Drag reduction
    Progress in Aerospace Sciences, 1996
    Co-Authors: Pr Viswanath
    Abstract:

    Abstract The problem of turbulent Base flows and the Drag associated with it have been of significant interest in missile as well as fighter aircraft design. Numerous studies in the literature have been devoted to aspects of reducing Base Drag on two-dimensional as well as on axisymmetric bodies. This paper presents a review of the developments that have taken place on the use of passive techniques or devices for axisymmetric Base and net afterbody Drag reduction in the absence of jet flow at the Base. In particular, the paper discusses the effectiveness of Base cavities, ventilated cavities, locked vortex afterbodies, multi-step afterbodies and afterbodies employing a non-axisymmetric boat-tailing concept for Base and net Drag reduction in different speed regimes. The broad features of the flow and the likely fluid-dynamical mechanisms associated with the device leading to Base Drag reduction are highlighted. Flight-test results assessing the effectiveness of some of the devices are compared with data from wind tunnels. The present survey indicates that Base and net afterbody Drag reduction of considerable engineering significance in aerospace applications can be achieved by various passive devices even when the (unmanipulated) Base flow is not characterised by vortex shedding.