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There are three distinct processes by which upward-propagating gravity waves influence the large-scale dynamics and energetics of the middle atmosphere: (i) nonlocalized transport of momentum through wave propagation in three dimensions that remotely redistributes atmospheric momentum in both zonal and meridional directions from wave generation to wave dissipation regions; (ii) localized diffusive transport of momentum, heat, and tracers due to mixing induced by wave breaking; and (iii) localized transport of heat by perturbing wave structures due to dissipation that redistributes the thermal energy within a finite domain. These effects become most significant for breaking waves when momentum drag, eddy diffusion, and wave heating-- the 'breaking trinity'--are all imposed on the background state. This paper develops a 3D parameterization scheme that self-consistently includes the breaking trinity in large-scale numerical models. The 3D parameterization scheme is developed based on the general relationship between the wave action flux and the subgrid-scale momentum and heat fluxes developed by Zhu in 1987 and a mapping approximation between the wave source spectrum and momentum deposition distribution developed by Alexander and Dunkerton in 1999. For a set of given input wind and temperature profiles at each model grid, the parameterization scheme outputs the vertical profiles of the subgrid-scale force terms together with the eddy diffusion coefficients in the momentum and energy equations for a 3D background flow. DOI: 10.1175/2010JAS3302.1

Aircraft on approach in high-drag, high-lift configurations create inherently noisy flow structures. For flaps, slats, and undercarriage, the strong correlation between overall noise and drag suggests that future quiet aircraft will need to generate drag at low noise levels. This paper presents a novel noise-reduction concept based on the idea that appreciable pressure drag can be generated by a relatively quiet swirling exhaust flow. A first aeroacoustic assessment of ram-pressure-driven swirling exhaust flows and their associated vortex breakdown instability is presented. The technical approach combines 1) an in-depth aerodynamic analysis, 2) qualitative acoustic source descriptions via plausibility arguments, and 3) detailed quantitative phased microphone-array measurements of a model-scale engine nacelle with stationary swirl vanes at a full-scale approach Mach number of 0.17. The analysis shows an acoustic signature composed of 1) quadrupole-type turbulent mixing noise in the swirling core flow and 2) scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near the nacelle, pylon, and vane centerbody trailing edges. The highest stable swirl-angle setting yields a nacelle-area-based drag coefficient of 0.83 with a full-scale overall sound pressure level of about 40 dBA at the International Civil Aviation Organization approach certification point. DOI: 10.2514/1.37249

The velocity, shape, and trajectory of the rising bubble in polyacrylamide (PAM) and carboxymethylcellulose (CMC) aqueous solutions were experimentally investigated using a set of homemade velocimeters and a video camera. The effects of gas the flowrate and solution concentration on the bubble terminal velocity were examined respectively. Results show that the terminal velocity of the bubble increases with the increase in the gas flowrate and the decrease in the solution concentration. The shape of the bubble is gradually flattened horizontally to an ellipsoid with the increase in the Reynolds number (Re), Eotvos number (Eo), and Morton number (Mo). With the increase in the Re and Eo, the rising bubble in PAM aqueous solutions begin to oscillate, but there is no oscillation phenomena for CMC aqueous solutions. By dimensional analysis, the drag coefficient of a single bubble in non-Newtonian fluids in a moderate Reynolds number was correlated as a function of Re, Eo, and Archimedes number (Ar) based on the equivalent bubble diameter. The predicted results by the present correlation agree well with the experimental data. [DOI: 10.1115/1.4000739] Keywords: bubble, rising velocity, non-Newtonian fluid, drag coefficient, correlation

Experimental investigation of drag reduction in vertical two-phase annular flow is presented. The work is a feasibility test for applying drag reducing additives (DRAs) in high production-rate gas-condensate wells where friction in the production tubing limits the production rate. The DRAs are intended to reduce the overall pressure gradient and thereby increase the production rate. Since such wells typically operate in the annular-entrained flow regime, the gas and liquid velocities were chosen such that the experiments were in a vertical two-phase annular flow. The drag reducers had two main effects on the flow. As expected, they reduced the frictional component of the pressure gradient by up to 74%. However, they also resulted in a significant increase in the liquid holdup by up to 27%. This phenomenon is identified as 'DRA-induced flooding.' Since the flow was vertical, the increase in the liquid holdup increased the hydrostatic component of the pressure gradient by up to 25%, offsetting some of reduction in the frictional component of the pressure gradient. The DRA-induced flooding was most pronounced at the lowest gas velocities. However, the results show that in the annular flow the net effect will generally be a reduction in the overall pressure gradient by up to 82%. The findings here help to establish an envelope of operations for the application of multiphase drag reduction in vertical flows and indicate the conditions where a significant net reduction of the pressure gradient may be expected. [DOI: 10.1115/1.3120299]

The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed. Keywords: superfluids/superfluidity; drag force; quantum fluctuations; dissipationless flow; Bose Einstein condensation

The drag prediction workshop series, held over the last six years and sponsored by the AIAA Applied Aerodynamics Committee, has been extremely useful in providing an assessment of the state of the art in computationally based aerodynamic drag prediction. An emerging consensus from the three-workshop series has been the identification of spatial discretization errors as a dominant error source in absolute as well as incremental drag prediction. This paper provides an overview of the collective experience from the workshop series regarding the effect of grid-related issues on overall drag prediction accuracy. Examples based on workshop results are used to illustrate the effect of grid resolution and grid quality on drag prediction, and grid convergence behavior is examined in detail. For fully attached flows, various accurate and successful workshop results are demonstrated, and anomalous behavior is identified for a number of cases involving substantial regions of separated flow. Based on collective workshop experiences, recommendations for improvements in mesh generation technology that have the potential to impact the state of the art of aerodynamic drag prediction are given. DOI: 10.2514/1.39201

The mean velocity profile and friction factor in turbulent flows with polymer additives are investigated using Prandtl's mixing-length theorem. This study reveals that the mixing-length theorem is valid to express the drag-reducing phenomenon and that the presence of polymer additives increases the damping factor B in van Driest's model; subsequently reducing the mixing-length, this interprets that the polymer hampers the transfer of turbulent momentum flux, the velocity is increased, and flow drag is reduced. This study also discusses the onset Reynolds number for drag reduction to occur. The predicted velocity, friction factor, and onset Reynolds number are in good agreement with the measured data in the literature. [DOI: 10.1115/1.3111255] Keywords: drag reduction, velocity distribution, van Driest's model, damping factor, friction factor

Mach's principle and the principle of relativity have been discussed by Hartman and Nissim-Sabat. Several phenomena were said to violate the principle of relativity as applied to rotating motion. These claims have recently been contested by Bhadra and Das. However, neither set of authors allowed for the general relativistic phenomenon of inertial dragging, and no calculation was offered to substantiate their claims. I discuss the possible validity of the principle of relativity for rotating motion within the context of the general theory of relativity and discuss the significance of inertial dragging in this connection. Although my main points are of a qualitative nature, I also provide the necessary calculations to demonstrate how these points arise as consequences of the general theory of relativity. [DOI: 10.1119/1.2996480]

A new indicator for adaptive mesh refinement is proposed based on a drag decomposition method. The indicator is entropy drag which can be obtained from the drag decomposition postprocessing. The drag decomposition method decomposes total drag into wave, profile, induced, and spurious drag components; the spurious one is due to unphysical entropy production resulting from numerical diffusion and errors. Moreover, the (spurious) entropy drag distribution can be visualized in the flowfield, and thus it is used as the indicator. The newly developed method for adaptive mesh refinement is investigated by inviscid transonic computations for the ONERA M6 wing. The result shows better performance than other mesh refinement methods such as the feature-based method. The authors conclude that the developed adaptive mesh refinement method employing the entropy drag as the indicator is promising for efficient reduction of mesh dependency. The important factors for computational meshes to predict drag accurately are then investigated in detail. DOI: 10.2514/1.31064

Spatial averaging of the Reynolds-averaged Navier-Stokes equations gives the double-averaged Navier-Stokes equations, for which boundary drag appears naturally and explicitly in momentum conservation equations. Increasing use of the double-averaged equations, e.g., for relating flows to three-dimensional bed roughness, for evaluation of profiles of flow stresses and velocities in ecologically significant regions below roughness tops, and for modeling purposes, requires parameterization of boundary drag at subelement scales. Based on seven flows over repeated square-rib roughness and ten flows over repeated fixed simulated sand waves, with measured velocities and bed pressures, expressions for form-drag coefficient [C.sub.D]=f (elevation below roughness top, relative roughness submergence, roughness steepness) are obtained for each of the two-dimensional roughness types. Using these equations, form drag variation with elevation below roughness tops can be calculated using either the double average of the square of local velocity (preferred based on conceptual considerations, trends in coefficient prediction, and also overall drag prediction) or the squared local double-averaged velocity, the roughness area being normal to the flow in each case. Integration of subelement drag given by these expressions is shown to give form-drag coefficient magnitudes and trends for complete individual elements comparable to those obtained by other authors based on measurements or numerical simulations. The ranges of roughness steepness and relative roughness submergence upon which the present equations have been derived need to be noted in consideration of application of the equations. In addition, effective application of the expressions is limited in regions of strongly negative double-averaged velocity. Further work remains to determine drag parameterization for alternative roughness geometries. DOI: 10.1061/(ASCE)0733-9429(2007)133:2(121) CE Database subject headings: Drag; Sand waves; Roughness.

A numerical study was conducted to investigate the effect of porosity strength on the drag reduction of projectiles having the secant-ogival-cylindrical-boat-tail shape. The Navier-Stokes equations for axisymmetric flows were applied. Darcy's law was used to model the interface of the main flow and the flow through the porous surface. The effect of changing the porosity strength upstream and downstream the shock position has been investigated on both cylindrical and boat-tail parts. The simulation method was applied to a projectile with a boat-tail angle [beta] = 7 deg at zero angle of attack, for Mach numbers ranging from 0.7 to 1.3 and a Reynolds number equal to 4.5 x [10.sup.6] based on the model length. It has been found that the porous surface is very effective in the case where the pressure drag is dominant, especially on the boat-tail. Moreover, the maximum drag reduction can be obtained by optimizing the porosity distribution for regions upstream and downstream of the shock wave position.

A theoretical method for predicting minimum induced-drag conditions in a nonplanar lifting systems is presented in this paper. The procedure is based on lifting line theory and the small perturbation acceleration potential. Under the hypotheses of linearity and rigid wake aligned with the freestream, optimality conditions are formulated using the Euler-Lagrange integral equation with constraints on fixed total lifting force and wing span. Particular attention is paid to analysis and numerical treatment of the Hadamard finite-part integrals involved in the solution process. The minimum induced-drag problem is then formulated and solved numerically and analytically. In the case of annular wings, closed-form expressions for the optimal circulation distribution, the normalwash, the induced-drag coefficient, and the efficiency are presented. Optimal annular wings and C-wings are extensively analyzed, and comparisons with available results in the literature are presented. It is confirmed that a C-wing presents almost the same induced drag (under optimal conditions) as the corresponding closed-wing system. However, the optimal distributions of circulation are significantly different. All optimal wing systems are also compared to an optimal cantilevered wing and a biplane.

We present the results of experimental investigations on the aerodynamic characteristics of high-drag devices with flexible membranes joined at their short ends (loops). The loops were placed in a low-speed wind tunnel and tested at speeds up to 19 m/s. The range of Reynolds numbers was Re = 2 x [10.sup.5]-2 x [10.sup.6]. The loops were tested for a variety of aspect ratios, from 3.3 to 30, three planform areas, and two mounting methods. Results are presented for the drag coefficient and for the flutter characteristics. We prove that with a low aspect ratio the loops form a teardrop shape and their flutter mode is a sinusoidal-like oscillation. Furthermore, the drag coefficient decreases with the increasing wind speed, but it depends strongly on the aspect ratio and the planform area. Empirical correlations for the drag coefficient are polynomial equations.

As an ideal configuration with a high lift-drag ratio, the waverider has become one kind of an attracted configuration for some special purposes. The main purpose of this paper is to investigate the design method for a cone-derived waverider at Ma = 6 and its basic aerodynamic characteristics, especially the improvement of the configuration for a higher lift-drag ratio. The investigation is finished by CFD and shows that first, the inverse-design method for the waverider configuration based on an inviscid conical shock wave is successful. Secondly, a great improvement of the lift-drag ratio from 2.95 to 4.06 can be obtained by modifying the prototype configuration.

To study the drag reduction effect of a bubbly fluid, a pin-disk experiment is performed on the Universal Micro Tribotester system. Bubbles are generated by water electrolysis in holes that are specially designed on the disk surface. Experiment result shows that the drag force experiences a dynamic process, both drag reduction and drag increment effects appear in the process depending on the bubble behavior. This process is numerically simulated using computational fluid dynamics (CFD), and the explanations for the drag variation are given based on the analysis of drag forces on each wall of the disk surface. The drag reduction occurs when the bubble fills the hole, as the viscous drag on the air-liquid surface is small, and the pressure drag is reduced as the side wall of the hole is covered by the bubble. The drag increment is thought to be caused by the increment of the fluid viscosity when the bubble leaves the hole and flows in the fluid. [DOI: 10.1115/1.2354531] Keywords: bubble, drag reduction, lubrication, surface roughness

The mechanism of drag reduction due to spanwise wall oscillation in a turbulent boundary layer is considered. Published measurements and simulation data are analyzed in light of Stokes' second problem. A kinematic vorticity reorientation hypothesis of drag reduction is first developed, It is shown that spanwise oscillation seeds the near-wall region with oblique and skewed Stokes vorticity waves. They are attached to the wall and gradually align to the freestream direction away from it. The resulting Stokes layer has an attenuated nature compared to its laminar counterpart. The attenuation factor increases in the buffer and viscous sublayer as the wall is approached. The mean velocity profile at the condition of maximum drag reduction is similar to that due to polymer The final mean state of maximum drag reduction due to turbulence suppression appears to be universal in nature. Finally, it is shown that the proposed kinematic drag reduction hypothesis describes the measurements significantly better than what current direct numerical simulation does. [DOI: 10.1115/1.2125974]

The technical objective of the Second AIAA Computational Fluid Dynamics (CFD) Drag Prediction Workshop is to assess the state-of-the-art computational methods as practical aerodynamic tools for aircraft force-and-moment prediction of increasingly complex geometries. With more emphasis being placed on CFD methods to evaluate aircraft designs early in the design process, the ability to accurately predict the forces and moments, specifically drag, on an airliner configuration is important. Using the CFD code Cobalt, force-and-moment calculations are obtained on a civil transport geometry with and without engine nacelle and pylon. Comparisons with experimental data show consistent agreement with forces and moments, wing Cp data, and qualitative data. Installation drag for the nacelle/pylon is well predicted. Relevance of the importance of the grid and robustness of the flow solver to the overall accuracy of the results is discussed.

The commercial computational fluid dynamics (CFD) code CFX-5 of ANSYS, Inc., has been used to compute the engine installation drag for the German Aerospace Center (DLR) F6 aircraft configuration as part of the Second AIAA Drag Prediction Workshop. The computations were performed with the standard hexahedral meshes provided by ICEM-CFD to the workshop. The full drag polar for the DLR-F6 configuration has been computed. For all cases, good agreement between the experiment and the predictions were obtained for lift, drag, and pitching moment coefficients. All simulations where based on the shear stress transport turbulence model, and additional computations have indicated that turbulence modeling issues are largely responsible for the overprediction of the lift curve slope that was observed by many of the workshop participants.

An approach to minimize the induced drag of an aeroelastic configuration by means of multiple leading- and trailing-edge control surfaces is investigated. A computational model based on a boundary-element method is constructed and drag-reducing flap settings are found by means of numerical optimization. Further, experiments with an elastic wind-tunnel model are performed in order to evaluate the numerically obtained results. Induced-drag results are obtained by analyzing lift distributions computed from optically measured local angles of attack because standard techniques proved insufficient. Results show that significant reductions of induced drag of flexible wings can be achieved by using optimal control surface settings.

The theoretical induced-drag benefits are presented for ideally loaded wings flying in formation and ground effect. An optimum-downwash approach using a vortex-lattice implementation was used to study formations of wings loaded optimally for minimum induced drag with roll trim. An exact approach was also developed to examine the drag of elliptically loaded wings in formation. The exact approach allows for decomposition of the benefits by considering the mutual-interference contributions from different pairs of wings in a formation. The results show that elliptically loaded wing formations have nearly the same drag as optimally loaded wing formations. For a formation of planar wings, in or out of ground effect, the optimum lateral separation corresponds to a 10% span overlap of wing tips. At this optimum lateral separation, a formation of 25 elliptically loaded wings flying out of ground effect experiences an 81% drag reduction compared to 25 wings flying in isolation. For large formations, in or out of ground effect, multiple local optima are seen for the lateral separation. Large formations experience small additional benefits caused by ground effect even at relatively large ground clearances of four wing spans. The shape of vee formations, for equipartition of drag benefits, is found to be nearly independent of flight in or out of ground effect.

Results from the Second AIAA Drag Prediction Workshop are summarized. The workshop focused on absolute and configuration delta drag prediction of the DLR, German Aerospace Research Center F6 geometry, which is representative of transport aircraft designed for transonic flight. Both wing-body and wing-body-nacelle-pylon configurations are considered. Comparisons are made using industry relevant test cases that include single-point conditions, drag polars, and drag-rise curves. Drag, lift, and pitching moment predictions from several different Reynolds averaged Navier-Stokes computational fluid dynamics codes are presented and compared to experimental data. Solutions on multiblock structured, unstructured, and overset structured grids using a variety of turbulence models are considered. Results of a grid-refinement study and a comparison of tripped transition vs fully turbulent boundary-layer computations are reported.

The results from DLR, German Aerospace Center, Airbus, and ONERA from the Second AIAA CFD Drag Prediction Workshop are presented. The lift, drag, and pitching moments are calculated for the DLR-F6 configuration at transonic flow conditions by solving the Reynolds-averaged Navier--Stokes equations on structured as well as on unstructured, hybrid grids. First, the drag is computed with the standard near-field method by integrating the surface pressure forces and shear stresses and second by a drag breakdown into its physical components, such as viscous, wave, and induced drag, by applying a far-field method. The influence of the grid is investigated, and the results are compared to experimental data. For all cases a slightly smaller angle of incidence is required in the computations as compared to the experiments to obtain the same lift coefficient. The drag polars and the engine installation drag can be computed accurately, but significant deviations exist for the pitching moments as a result of an underestimation of the flow separation at the trailing edge of the upper wing upper. Comparing the far-field drag breakdown results for structured and unstructured solution methods shows that viscous and wave drag are computed nearly identical. The far-field method gives a better understanding of the sources of drag and offers a substantial benefit for aerodynamic design.

This paper summarizes the results obtained with the NSU3D unstructured multigrid solver for the First AIAA Drag Prediction Workshop held in Anaheim, California, in June 2001. The test ease for the workshop consists of a wing-body configuration at transonic flow conditions. Flow analyses for a complete test matrix of lift coefficient values and Mach numbers at a constant Reynolds number are performed, thus producing a set of drag polars and drag rise curves, which are compared with experimental data. Results were obtained independently by both authors using an identical baseline grid and different refined grids. Most cases were run in parallel on commodity cluster-type machines, whereas the largest cases were run on an SGI Origin machine using 128 processors. The objective of this paper is to study the accuracy of the subject unstructured grid solver for predicting drag in the transonic cruise regime, to assess the efficiency of the method in terms of convergence, CPU time, and memory, and to determine the effects of grid resolution on this predictive ability and its computational efficiency. A good predictive ability is demonstrated over a wide range of conditions, although accuracy was found to degrade for cases at higher Mach numbers and lift values where increasing amounts of flow separation occur. The ability to rapidly compute large numbers of eases at varying flow conditions using an unstructured solver on inexpensive clusters of commodity computers is also demonstrated.

Navier-Stokes calculations on hybrid grids using the TAU software of the MEGAFLOW project are performed to compute engine installation drag for the DLR, German Aerospace Research Center, F6 transport aircraft configuration at cruise flight conditions with conventional and with very-high-bypass-ratio nacelles at three and two different locations, respectively. The results are verified by a comparison with experimental data from different wind-tunnel campaigns carried out with Office National d'Etudes et de Recherches Aerospatiales. Numerical discretization errors are reduced by several steps of grid adaptation, resulting in grid densities up to 8.4 x [10.sup.6] nodes. It is demonstrated that the installation drag of the different configurations, which vary only a few drag counts([10.sup.-4]), can be computed consistently, although the total drag forces are predicted lower than results of experiments. Successive grid refinement leads to a decrease of the differences between calculated and measured installation drag.

With the use of a pressure-ruptured shock tube, an experimental study of the dynamics of shock waves in weakly ionized argon, krypton, xenon, and neon glow discharge plasmas has been performed. For Mach numbers in the range 1.5-3, our results show that there is an increase in the velocity of a shock wave when it makes a transition from a neutral gas to a weakly ionized plasma, and the effect increases with increasing atomic weight. The observations indicate that the shock acceleration cannot be accounted for by thermal effects. However, the use of turbulence models based on reduced kinetic theory and second-order phase transitions suggests a consistent role for turbulence in plasma-induced hypersonic drag reduction.

An efficient aerodynamic design optimization method for the compressible Euler equations is presented. A gradient-based optimization method is used to find the optimal design, in conjunction with a continuous adjoint sensitivity analysis method. To improve the efficiency of the design method, a tightly coupled algorithm based on a step-size estimation is proposed. The efficiency of the present method is demonstrated through drag minimizations of a wing and an airfoil. The result shows that the cost of the present method is significantly lower than that of the loosely coupled algorithm.

The last two decades have seen considerable research activity on the use of riblets for viscous drag reduction. Experimental results concerning the performance of 3M riblets on airfoils, wings and wing-body or aircraft configurations at different speed regimes are reviewed; these applications bring in additional effects like pressure gradients and three dimensionality. In addition to drag reduction, aspects of altered flow features due to riblets are discussed based on detailed wind tunnel measurements at low speeds. The available results obtained from wind tunnels as well as flight tests firmly establish the effectiveness of riblets from low speed to moderate supersonic Mach numbers. With optimized riblets, skin friction drag reduction in the range of 5-8% have been measured on 2D airfoils at low incidence and in mild adverse pressure gradients; strong evidence exist at low speeds to indicate that riblets are more effective in adverse, pressure gradients. On wings of moderate sweep relevant to transport aircraft, riblets remain effective providing drag reduction comparable to 2D airfoils, as long as the local angle between the surface streamlines and riblet orientation is relatively small (< 10[degrees]). Limited data available on wing-body configurations show that total drag reduction of about 2-3% is likely. Certain suggestions for future research are outlined.

The summary of combined experimental and computational investigations is presented for the plasma injection from a hypersonic blunt body for drag reduction. The systematic pursuit addresses all speculated mechanisms that can generate favorable magnetoaerodynamic interactions: the counterflow jet shock aerodynamic interaction, the nonequilibrium thermodynamic and chemical phenomenon, and the electromagnetic-aerodynamic interaction. The computational study was carried out by solving both the three-dimensional and the axisymmetric, mass-averaged, Navier-Stokes equations for counterflow jet interaction. The experimental investigation of the plasma injection was conducted in a nominal Mach 6 open jet, blowdown tunnel. The weakly ionized, counterflow jet generated by a plasma torch has a vibrational temperature of 4400 K, an electron temperature around 20,000 K, and electron number density greater than 3 x [10.sup.12]/[cm.sup.3]. It is found that the drag reduction is mostly derived from the viscous-inviscid interaction of the counterflow jet and thermal energy deposition. The nonequilibrium and the electromagnetic effect by an applied magnetic field are negligible.

Tidal velocities were used to calculate total barotropic tidal energy loss within the deep Pacific Ocean, at depths below 1000 m. The Hawaiian Ridge region is used as a control to determine potential influence of bathymetry representation, and energy loss was calculated using sea floor topography. No major differences were found between tidal velocities and sea floor topography as an energy loss calculation method.

A study of biplanes and their drag characteristics is presented with reference to their aerodynamic efficiency. A supersonic biplane configuration is described and examined for its lift and drag.

A new study aims to evaluate the wave drag of a three-dimensional wing using only data from accurate two-dimensional flow analyses.

The inverse design method is applied to a design problem of transonic wing planform and section shape design.

A new study investigates the characteristics of the two-dimensional performance of a circulation controlled cylinder with a removable flap and two slots.

A new study investigates delayed flow separation causes by the shockwave/boundary-layer interaction.

Results of investigations into drag reduction of helicopter fuselages are presented.

Research is presented concerning the lift augmentation of a Gurney flap leading-edge fences on a 60-degree delta wing in a wind tunnel. Pitching moment, drag, surface pressures and lift are discussed.

Research is presented concerning transonic rectangular cavity flow characteristics. The influence of length-to-depth and length-to-width cavity ratios in determining cavity characteristics is discussed.

Research concerning the use of low-speed wind-tunnel tests to study the drag caused by the laser turret of an aircraft is presented. The effectiveness of splitter plates and fairings in reducing drag is discussed.

Research concerning the pitch of propellers on light airplanes is presented. Fixed-pitch propellers are compared with varying pitch propellers. Numerical equations which determine the most favourable propeller pitch ratio selection are discussed.

Friction drag prediction is important in the design of aerodynamic configurations. The abilities of a solver of the Reynolds-averaged Navier-Stokes equations (RANS) to predict friction drag over an airfoil, were studied by comparison with values provided by a coupled potential/boundary-layer method. The best local agreement was obtained with the Reynolds-stress model.

Aerodynamic effects of a forward-looking infrared (FLIR) sensor, and an AAR47 sensor fairing were examined, as part of existing V-22 computational fluid dynamics (CFD) modeling. The FLIR was found to to slightly increase drag at a 0-degree angle of attack, and vortices were created with the addition of FLIR and AAR47, resulting in a favourable effect on lift at moderate attack angles.

Methods used to determine F/A-18E flight lift an drag characteristics are reported, and wind-tunnel-predicted drag and performance were correlated with early flight results. Uniquely high-quality data was produced using conventional and accepted industry standards.

Techniques used to determine F/A-18E wind-tunnel lift and drag characteristics to generate aircraft performance predictions are described. High-fidelity models, comprehensive test programs and integration of computational fluid dynamics ensured first-time quality test results. Good agreement between wind-tunnel and flight results enable the performance flight evaluation plan to be reduced by 60 flights.

Drag reduction was investigated for the combined system of polymer additives and a riblet pipe. The riblet grooves were V-shaped, the spacing of which was 1.3 mm and the height of which was 1.01 mm. For higher [h.sup.+], a triangular riblet system including other geometries increases the drag to levels similar to those of normal transient roughness. This drag increase was generally given as a function of [h.sup.+]. The polymer additives were Aronfloc N-110 and Separan AP-30. The critical shear stress [[Tau].sup.*], at which N-110 started the drag reduction, was approximately eight times higher than [[Tau].sup.*] for AP-30. In the combined system, the synergistic drag reduction for higher [h.sup.+] was discussed under the assumption that the additives suppressed the drag increase resulting from riblets. Since the additives thicken a wall layer covering the region from a viscous sublayer to a buffer layer, the relative height of h to this wall layer thickness is lowered. In addition, the flow enhancement due to additives relatively suppresses the riblet-induced drag increase. The analysis based on velocity profiles indicated that these effects can produce synergistic drag reduction for higher [h.sup.+].

Laminar drag reduction has been shown for the flow of a Newtonian fluid in the space between two vertical coaxial cylinders. Experiments were carried out to measure the torque of a bob with a highly water-repellent wall to clarify the effect of the contact surface of the bob on the flow behavior. The basic material of the highly water-repellent wall is fluorine alkane modified acrylic resin with added hydrophobic silica, and the contact angle of the wall is about 150 degree. The radius ratios of the bob were 0.932 and 0.676. Test fluids were Newtonian aqueous solutions of 60, 70, and 80 wt% glycerin and polymer solutions. The maximum drag reduction ratio was about 12%for 80 wt% glycerin solution at a radius ratio of 0.932. The moment coefficient of the coaxial cylinder in Newtonian fluids was analyzed for fluid slip, and it was shown that the analytical results agreed well with the experimental data. For the case of non-Newtonian fluids, the fluid slip velocity of polymer solutions is not proportional to the shear stress and the relationship is approximated by power-law equations.

Much research has been undertaken into the effectiveness of riblets in the reduction of turbulent drag and their use is now well-established. A new study investigates the total drag reduction due to riblets on a cambered airfoil at low speed and at high angles of attack. The study again demonstrates the effectiveness of riblets in adverse pressure gradients up to a certain value, beyond which effectiveness reduces.

The use of 3M riblets on reducing viscous drag on a swept wing with a general aviation wing airfoil section at low speeds has been assessed. The surface-pressure distributions, total drag, mean velocity, turbulence intensity and Reynold shear-stress profiles were measured at a chord Reynolds number of 0.75 X 10 raised to the 6th power, at an incidence range of 0 to 6 deg. Results indicate maximum and total viscous drag reductions of 6 and 8%, respectively, at zero incidence. These results are comparable to those obtained on two-dimensional flat plates and airfoils.

The accuracy of the surface integration and wake integration methods in predicting aerodynamic drag from computations of two-dimensional RaNS equations, were compared. Wake integration was found to be a simpler method for calculating drag as not surface geometry is required, and it allows total drag decomposition into its physical components.

An extension of a standard air track experiment is described in which the effects of air resistance can be studied. A circular disk is placed on one end of an air track cart to provide air drag. The data analysis consists of subtracting the 'ideal' velocity for a frictionless situation from the measured velocity and plotting the difference as a function of the ideal velocity. The resulting curve is fitted with a modified power-law and the coefficient of the cubic term is studied as a function of the area of the disk, a behavior that can be predicted theoretically. Frictional effects in addition to the air drag on the disk were found to be significant and were accounted for.

We review the problem of a vertically thrown ball, with a drag force which is either linear or quadratic in the speed. It is stressed from the outset that these two types of drag correspond to specific ranges of the Reynolds number (Re