A preconditioned dual-time, diagonalized ADI scheme for unsteady computations

Buelow, Philip E.; Schwer, Douglas A.; Feng, Jianmei; Merkle, Charles L.; Choi, D.

doi:10.2514/6.1997-2101

Cited by 42 publications

(21 citation statements)

References 2 publications

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“…Many of the low Mach number preconditioning methods have been summarized by Turkel [73][74][75]. The present work implements a preconditioned dual-time scheme in the diagonalized approximate factorization framework, described by Buelow et al [76] and Pandya et al [77]. The preconditioning is based on the one developed by Turkel [73].…”

Section: Low Mach Preconditioningmentioning

confidence: 99%

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Lakshminarayan

Baeder

2010

Journal of Aircraft

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In this work, a compressible Reynolds-Averaged Navier Stokes (RANS) solver is extended to investigate the aerodynamics of a micro-scale coaxial rotor configuration in hover. This required the following modifications to the solver: implementation of a time-accurate low Mach preconditioner, implementation of a sliding mesh interface boundary condition, improvements in the grid connectivity and parallelization of the code.First, an extensive validation study on the prediction capability of the solver is performed on a hovering micro-scale single rotor, for which performance data and wake characteristics have been measured experimentally. The thrust and power are reasonably well predicted for different leading and trailing geometries.Blunt leading edge geometries show poorer performance compared to the sharp leading edge geometries; the simulations show that this is mainly because of the large pressure drag acting at the blunt front. The tip vortex trajectory and velocity profiles are also well captured. The predicted swirl velocities in the wake for the micro-rotor are found to be significantly larger as compared to those for a full-scale rotor, which could be one of the reasons for additional power loss in the smaller scale rotors. The use of twist and taper is studied computationally and is seen to improve the performance of micro-rotor blades.Next, the solver is applied to simulate the aerodynamics of a full-scale coaxial rotor configuration in hover, for which performance data is available from experiments. The global quantities such as thrust and power are predicted reasonably well. In the torque trimmed situation, the top rotor shares significant percentage of the total thrust at lower thrust levels, which decreases to about 55% of the total thrust at higher thrust values. The simulations reveal that the interaction between the rotor systems is seen to generate significant impulses in the instantaneous thrust and power. The characteristic signature of this impulse is explained in terms of the blade thickness effect and loading effect, as well as blade-vortex interactions for the bottom rotor (wake effect).Finally, the RANS solver is applied to investigate the aerodynamics of a micro-scale coaxial rotor configuration in hover. The overall performance is well predicted. The interaction between the rotor systems is again seen to generate 3-8% fluctuation in the instantaneous thrust and power. The wake effect in the simulation is seen to be very prominent and the phasing of the impingement of the tip vortex from the top rotor upon the bottom rotor plays a significant role in the amount of unsteadiness on the bottom rotor. Interaction of the top rotor vortex and inboard sheet with the bottom rotor results in significant shedding on the bottom rotor blade, and this is believed to be caused by the of sharp leading edge geometry. Significant blade-vortex and vortex-vortex interactions are observed for coaxial systems.

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Section: Low Mach Preconditioningmentioning

confidence: 99%

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Lakshminarayan

Baeder

2010

Journal of Aircraft

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“…The simplifications that can be introduced in the explicit stage linearization are likely to induce a loss of intrinsic efficiency which will have to be balanced through a lower unit cost, so as to preserve the global efficiency. Following this line of idea, Pulliam and Chaussee proposed in 1981 a diagonalized implicit treatment applied to alternate direction factorization method [3], which was next extended to the case of preconditioned schemes within a dual-time framework and successfully applied to the computation of unsteady low-Mach number flows on structured grids [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Low‐cost implicit schemes for all‐speed flows on unstructured meshes

Kloczko

Corre

Beccantini

2008

Numerical Methods in Fluids

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SUMMARYMatrix-free implicit treatments are now commonly used for computing compressible flow problems: a reduced cost per iteration and low-memory requirements are their most attractive features. This paper explains how it is possible to preserve these features for all-speed flows, in spite of the use of a lowMach preconditioning matrix. The proposed approach exploits a particular property of a widely used low-Mach preconditioner proposed by Turkel. Its efficiency is demonstrated on some steady and unsteady applications.

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“…At low Mach numbers, 3 AIAA-99-0084 the jet will be compressed by the inlet air. This will decrease the cross-sectional area of the jet streamtube and cause some of the inlet air to flow around the splitter plate and not enter the combustor.…”

Section: Aiaa-99-0084mentioning

confidence: 99%

Computational analysis of fluidic compression in supersonic flowfields

Haws

Noall

Daines

1999

37th Aerospace Sciences Meeting and Exhibit

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A technique is introduced in which a supersonic flow is compressed in a supersonic inlet by a high pressure jet. This fluidic compression technique is analyzed in the present work using computational techniques. It is shown that by adjusting the pressure of the compression jet, the flow can be kept near design conditions in a fixed-geometry configuration. Results show that this method increases the minimum flowpath area, maintains shock-onlip over a range of Mach numbers, and reduces shock wave/boundary layer interactions. The potential advantages include lower spillage at low Mach numbers, reduced tendency to unstart, and the ability to have near-design operation over a wide range of flight Mach numbers without resorting to variable-geometry machinery. In addition, for combined-cycle engines it yields a low-blockage ftowpath for ejector and ramjet modes while maintaining high compression in scramjet mode. Global analysis is used to provide qualitative performance estimates. Grid doubling is used to analyze spatial resolution. INTRODUCTIONSince the beginning of human flight, the demand for flight vehicles has steadily increased. Today, there is a growing demand for low-cost earthto-orbit and near-orbital :Bight. Some uses for earth-to-orbit vehicles include satellite deployment and recovery, space station maintenance, military applications, and space tourism. Near-orbital flight offers fast long-distance travel for civilians, as well as advanced reconnaissance and long-range payload delivery for the military.Rocket engines have been used for years on space-bound vehicles and other vehicles requiring hypersonic speeds; however, rockets deliver low specific impulse, restricting the payload to only a small fraction of the launch weight. Combinedcycle engines are some of the most promising engines for low-cost hypersonic :Bight. Scramjet engines are a critical stage of combined-cycle engines because, despite their potential a scramjet has not yet been developed which delivers on the promise of high specific impulse. The scramjet, or supersoniccombustion ramjet, engine is an experimental airbreathing engine proposed for use on hypersonic vehicles. Its distinguishing feature is supersonic combustion, which becomes necessary at hypersonic speeds to avoid extreme temperatures in which exothermic reactions are impossible. 1• Graduate Student, Student Member AJAA t Graduate Student ! Assistant Professor, Member A1AA Copyright @1999 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 1With the development of scramjet technology, several challenges have arisen. These include achieving efficient compression and efficient air capture over a wide Mach number range, mixing and combustion of fuel, materials, and cooling. The present research is motivated by the need for low spillage at low Mach numbers and high compression at high Mach numbers without variable geometry. The large inlet capture area required for compression at high Mach numbers presents significant challenges at off-design Mach nu...

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A preconditioned dual-time, diagonalized ADI scheme for unsteady computations

Cited by 42 publications

References 2 publications

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Low‐cost implicit schemes for all‐speed flows on unstructured meshes

Computational analysis of fluidic compression in supersonic flowfields

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