Wave drag on a submerged sphere

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

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A numerical study on the single pulsed energy addition based unsteady wave drag reduction at varied hypersonic flow regimes

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020973134 ◽

2020 ◽

pp. 095441002097313

Author(s):

Dathi SNV Rajasekhar Rao ◽

Bibin John

Keyword(s):

Steady State ◽

Mach Number ◽

Drag Reduction ◽

Shock Layer ◽

Blunt Body ◽

Wave Drag ◽

Flow Features ◽

Energy Pulse ◽

Energy Addition ◽

Wave Drag Reduction

In this study, unsteady wave drag reduction in hypersonic flowfield using pulsed energy addition is numerically investigated. A single energy pulse is considered to analyze the time-averaged drag reduction/pulse. The blast wave creation, translation and its interaction with shock layer are studied. As the wave drag depends only on the inviscid aspects of the flowfield, Euler part of a well-established compressible flow Navier-Stokes solver USHAS (Unstructured Solver for Hypersonic Aerothermodynamics) is employed for the present study. To explore the feasibility of pulsed energy addition in reducing the wave drag at different flight conditions, flight Mach numbers of 5.75, 6.9 and 8.0 are chosen for the study. An [Formula: see text] apex angle blunt cone model is considered to be placed in such hypersonic streams, and steady-state drag and unsteady drag reductions are computed. The simulation results indicate that drag of the blunt-body can be reduced below the steady-state drag for a significant period of energy bubble-shock layer interaction, and the corresponding propulsive energy savings can be up to 9%. For energy pulse of magnitude 100mJ deposited to a spherical region of 2 mm radius, located 50 mm upstream of the blunt-body offered a maximum percentage of wave drag reduction in the case of Mach 8.0 flowfield. Two different flow features are found to be responsible for the drag reduction, one is the low-density core of the blast wave and the second one is the baroclinic vortex created due to the plasma energy bubble-shock layer interaction. For the same freestream stagnation conditions, these two flow features are noted to be very predominant in the case of high Mach number flow in comparison to Mach 5.75 and 6.9 cases. However, the ratio of energy saved to the energy consumed is noted as a maximum for the lower Mach number case.

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Thermal and structural response of aerospike mounted on blunt-nose body

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020976488 ◽

2020 ◽

pp. 095441002097648

Author(s):

Zhang ZhunHyok ◽

Won CholJin ◽

Ri CholUk ◽

Kim CholJin ◽

Kim RyongSop

Keyword(s):

Aerodynamic Force ◽

Coupling Effect ◽

Angle Of Attack ◽

Structural Response ◽

Response Characteristic ◽

Wave Drag ◽

Hypersonic Vehicle ◽

Loosely Coupled ◽

Calculation Results ◽

Blunt Nose

The inclusion of aerospike on blunt nose body of hypersonic vehicle has been considered to be the simplest and most efficient technique for a concurrent reduction of both aeroheating and wave drag due to hypersonic speed. However, the thermal and mechanical behavior of aerospike structure under the coupling effect of aerodynamic force and aeroheating remains unclear. In this study, the thermal and structural response of aerospike mounted on the blunt nose body of hypersonic vehicle was numerically simulated by applying 3 D fluid-thermal-structural coupling method based on loosely-coupled strategy. In the simulation, the angle-of-attack and the spike’s length and diameter are differently set as α = 0°–10°, L/D = 1–2 and d/D = 0.05–0.15, respectively. Through the parametric study, the following results were obtained. Firstly, the increase of vehicle’s angle-of-attack and spike’s length unfavorably affect the thermal and structural response of aerospike. Secondly, the increase of spike’s diameter can improve its structural response characteristic. Finally, the aerospike with the angle-of-attack of 0° and the length and diameter of L/D = 1 and d/D = 0.15, respectively, is preferred in consideration of the effect of flight angle-of-attack and spike’s geometrical structure on the thermal and structural response of spike and the drag reduction of vehicle. The numerical calculation results provide a technical support for the safe design of aerospike.

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Time Domain Simulations on a Single Point Moored Submerged Sphere of Variable Radius

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2 ◽

10.1115/omae2005-67434 ◽

2005 ◽

Author(s):

Joa˜o M. B. P. Cruz ◽

Anto´nio J. N. A. Sarmento

Keyword(s):

Wave Propagation ◽

Time Domain ◽

Physical Phenomenon ◽

Single Point ◽

Vertical Direction ◽

Equation Of Motion ◽

Hydrodynamic Coefficients ◽

Energy Converter ◽

Submerged Sphere ◽

The Time Domain

This paper presents a different approach to the work developed by Cruz and Sarmento (2005), where the same problem was studied in the frequency domain. It concerns the same sphere, connected to the seabed by a tension line (single point moored), that oscillates with respect to the vertical direction in the plane of wave propagation. The pulsating nature of the sphere is the basic physical phenomenon that allows the use of this model as a simulation of a floating wave energy converter. The hydrodynamic coefficients and diffraction forces presented in Linton (1991) and Lopes and Sarmento (2002) for a submerged sphere are used. The equation of motion in the angular direction is solved in the time domain without any assumption about its output, allowing comparisons with the previously obtained results.

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Some Experiments on Artificially Roughened Lucy Ashton Geosims

Journal of Ship Research ◽

10.5957/jsr.1980.24.3.170 ◽

1980 ◽

Vol 24 (03) ◽

pp. 170-180

Author(s):

A.J. Smits ◽

N. Matheson ◽

P.N. Joubert

Keyword(s):

Pipe Flow ◽

Wave Drag ◽

Mirror Image ◽

Turbulent Pipe Flow ◽

Viscous Resistance ◽

Local Parameter ◽

Image Model ◽

Outer Flow ◽

Total Drag ◽

Towing Tank

A mirror-image model of the Lucy Ashton was covered with two different "mesh-type" roughnesses and tested in a wind tunnel. Total drag and velocity profile measurements are presented. Total drag results are also given for a normal Lucy Ashton model with the same roughness mesh tested in a towing tank. The influence of roughness on the wave drag component was found to be small, implying that the "interdependence" of wavemaking and viscous resistance is small. The importance of considering roughness as a local parameter is demonstrated, and the roughness function results agree well with the fully developed turbulent pipe flow results of Perry and Abell, even though the ship boundary-layer outer flow did not follow any recognized wake function.

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Effects of Non-orographic Gravity Wave Drag on Seasonal and Medium-range Predictions in a Global Forecast Model

Asia-Pacific Journal of Atmospheric Sciences ◽

10.1007/s13143-018-0023-1 ◽

2018 ◽

Vol 54 (S1) ◽

pp. 385-402 ◽

Cited By ~ 4

Author(s):

Hyun-Joo Choi ◽

Ji-Young Han ◽

Myung-Seo Koo ◽

Hye-Yeong Chun ◽

Young-Ha Kim ◽

...

Keyword(s):

Gravity Wave ◽

Forecast Model ◽

Wave Drag ◽

Medium Range

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The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7797-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 7797-7818 ◽

Cited By ~ 47

Author(s):

N. P. Hindley ◽

C. J. Wright ◽

N. D. Smith ◽

N. J. Mitchell

Keyword(s):

Southern Ocean ◽

Gravity Wave ◽

General Circulation ◽

Hot Spot ◽

Polar Vortex ◽

General Circulation Models ◽

Wave Drag ◽

Southern Andes ◽

Analysis Technique ◽

Modelling Studies

Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

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