Variation Of Drag Research Articles

An Estimate of Mountain Drag during ALPEX for Comparison with Numerical Models

Abstract The pressure drag vector for a limited domain including the Alps is estimated for the ALPEX period of March and April 1982. All of the reported, three hourly, surface pressure data in the domain are used and maps of analyzed deviation surface pressure are obtained for the mountainous area. The very important drag values previously reported are confirmed and shown to occur when tight pressure gradients are localized above the steep orography. The peak values are found to be sensitive to the resolution of the analysis. A composite of the large drag variations occurring in relation to frontal passage and cyclogenesis is constructed. The diurnal cycle observed during periods of quiet synoptic activity is discussed. The observed drag compares favorably with the drag in the simulation of a case of cyclogenesis using a numerical model with comparable horizontal resolution.

Folding in the Greenland Ice Sheet

The deformation of layering into folds is modeled for a linear viscous medium moving over a décollement. Folds are generated by flow variations caused by relief on the décollement, variations in friction, or both. The model is applied to folds forming now in the Greenland Ice Sheet near Dye 3, for which more complete data are available than for analogous solid earth situations and for which the décollement is at or near the bed. The folds (wavelength 4–8 km) are detected by radio reflection sounding. Measured surface deformation and deformation rate are used with the radar results to test the theory. Calculated fold amplitude is only 20% less than that measured, which indicates that the theory is substantially correct. Inversion of the data to calculate basal drag and velocity variations is not helpful for near Dye 3 because many different basal boundary conditions can lead to the observed deformations.

Concerning the effect of surface drag on the circulation of a baroclinic planetary atmosphere

AbstractExtended runs of a multi‐level spectral numerical model of atmospheric flow on a hemisphere have been used to investigate the effect of surface drag variations on the nature of the time‐averaged flow. It is shown that the most drastic effect of reducing the surface drag is to permit strong horizontal, barotropic shears in the zonal mean flow, which inhibit baroclinic instability. This superficially paradoxical result is implicit in many earlier calculations, most clearly in the lifecycle description of nonlinear baroclinic instability, but appears not to be widely appreciated. The kinetic energy spectra are interpreted in terms of the wavenumber of the most baroclinically unstable normal modes KR, the Rhines blocking wavenumber Kβ, and a limiting wavenumber based on surface drag KD. The changes in KR and the smaller changes in Kβ as drag is reduced account satisfactorily for the changes found in the kinetic energy spectra.

Navier-Stokes computations of projectile base flow with and without mass injection

A computational capability has been developed for predicting the flowfield about projectiles, including the recirculatory base flow at transonic speeds. In addition, the developed code allows mass injection at the projectile base and hence is used to show the effects of base bleed on base drag. Computations have been made for a secant-ogive-cylinder projectile for a series of Mach numbers in the transonic flow regime. Computed results show the qualitative and quantitative nature of base flow with and without base bleed. Base drag is computed and compared with the experimental data and semiempirical predictions. The reduction in base drag with base bleed is clearly predicted for various mass injection rates. Results are also presented that show the variation of total aerodynamic drag both with and without mass injection for Mach numbers of 0.9 < M< 1.2. The results obtained indicate that, with further development, this computational technique may provide useful design guidance for projectiles. MAJOR area of concern in shell design is the accurate prediction of the total aerodynamic drag. Both the range and terminal velocity of a projectile (two critical factors in shell design) are directly related to the total aerodynamic drag. The total drag for projectiles can be divided into three components: 1) pressure drag (excluding the base region), 2) viscous (skin friction) drag, and 3) base drag. At transonic speeds, base drag constitutes a major portion of the total drag. For a typical shell at M = 0.90, the relative magnitudes of the aerodynamic drag components are: 20% pressure drag, 30% viscous drag, and 50% base drag. The critical aerodynamic behavior of projectiles, indicated by rapid changes in the aerodynamic coefficients, occurs in the transonic speed regime and can be attributed in part to the complex shock structure existing on projectiles at transonic speeds. Therefore, in order to predict the total drag for projectiles, computation of the full flowfield (including the base flow) must be made. There are few reliable semiempirical procedures that can be used to predict shell drag; however, these procedures cannot predict the effects of mass injection. The objective of this research effort was to develop a numerical capability, using the Navier-Stokes computational technique, to compute the flowfield in the base region of projectiles at transonic speeds and thus to be able to compute the total aerodynamic drag with and without mass injection. The pressure and viscous components of drag generally cannot be reduced significantly without adversely affecting the stability of the shell. Therefore, recent attempts to reduce the total drag have been directed toward reducing the base drag. A number of studies have been made to examine the total drag reduction due to the addition of a boattail.1 Although this is very effective in reducing the total drag, it has a negative impact on the aerodynamic stability, especially at transonic

Computer simulation of the trajectories of large water jets

A three-dimensional computer simulation of the motion of a water jet is described which includes the effects of wind from any direction. The simulation is useful in the design of fire-fighting systems, particularly those used in offshore situations. The equations of motion are presented in vector form and the problem of the fluid dynamic drag variation is discussed. Semi-empirical approximations for the drag components along and across the jet are presented which involve four unknown constants. These are reduced to three by using previous data on the efficiency of vertical jets. To fix the remaining constants, information was available from a series of large jets tests carried out to prove an offshore fire fighting system. In these tests different nozzle shapes were tried and, using the best of these shapes, a large number of trajectories were measured photographically. These were used to fix the simulation drag constants and good agreement is shown between measurements and predictions. The simulation enables the effects of flow-rate, pressure, nozzle size, elevation and wind strength to be evaluated in the system design

On the local meteorology at the marginal ice zone of the Bering Sea

In March 1981, detailed meteorological observations were made at the marginal ice zone in the Bering Sea during a period of northerly winds. A 20% increase in wind speed from 90 km inside the edge to 90 km over the ocean was observed. The temperature increased from −11°C to −5°C, and the boundary layer height over the ocean increased from 450 m to 600 m. Data support the concept of a diverging (accelerating) flow. A simple integrated slab model of the atmospheric boundary layer which includes the effects of clouds, surface heat flux, and radiative cooling is applied to the conditions of the marginal ice zone. The model shows that most of the observed variation in the marginal ice zone can be explained by drag variation over the ice and heat flux over the open ocean. Heat flux in the marginal ice zone and cloud processes affect the results only slightly.

Aerodynamic forces on a cylindrical structure in a wake of another cylindrical structure

Measurements of mean aerodynamic force components on a smooth circular cylinder in the near wake of an identical parallel cylinder are presented for different configurations of longitudinal and lateral spacings and over a range of subcritical Reynolds numbers 13 000 to 72 000. The observed symmetrical variations of drag and antisymmetrical variations of lift are empirically correlated on the basis of the geometrical parameters and the flow Reynolds number. Additional information from surface pressure distributions gives more detail and permits deductions to be made on the effects of the main parameters involved in the observed phenomena. Almost all aerodynamic parameters of the cylinder in the wake are strongly altered compared to the respective ones of a single cylinder in uniform flow. The data presented are intended for direct use by practising engineers. They also contribute to the further understanding of the effects of turbulent shear flows on bluff cylinders and the formation of their wakes. While dominant effects could be traced on the basis of measured data, the complexities of the flow studied did not permit separation of all factors contributing to the observed behaviour.

Performance of a Hydrofoil Sailing Boat (1 St Report)

The performance of a hydrofoil sailing boat, which has dihedral-angled and surface-piercing foils, at high speed is described.A simple method of performance prediction was devised, which considered two important factors for sailing boats as follows : (i) variation of hydrodynamic drag caused by change of heel and leeway angles ; (ii) limitation of sailing performance due to capsizing.For the present study one typical sailing hydrofoil configuration was used, i. e. a 5. 08m long catamaran, with a pair of surface-piercing front (main) foils having 40 degree dihedral angles, and one horizontal rear foil, which formed an inverted “T” in combination with the rudder.The calculations aimed to predict the effect of dihedral angles, width between the foils, and weight of the boat on performance.The results obtained were as follows : (1) the present method gives good estimated values for the performance of a hydrofoil sailing boat with dihedral-angled and surface-piercing foils ; (2) the sails should be trimmed to produce the maximum thrust force, but the performance of a boat to a beam reach is subject to limitation due to capsizing, and to windward, due to leeway angle ; (3) although the true wind angle varies extensively, the apparent wind angle at high speed varies much less, so that the aerodynamic drag angle of the sail can be regarded approximately constant; (4) the predicted heel angle is between 0 and-6 degrees at high speed (heel to weather-side); (5) the aerodynamic force coefficients of the sail estimated from the seatrial are smaller than the wind tunnel test data ; (6) there are small differences between the predicted and measured immersion of the hydrofoils ; (7) the weight of a boat has an appreciable effect on the light wind performance ; (8) the dihedral angles and width between the foils have a considerable effect of the boat performance. The optimum dihedral angle is between 40 and 45 degrees, and the optimum width between foils is around 1. 21. 6 hs, hs beeing the height of C. E., the centre of sail force, above the foil bottom.

Comment on "Ideal Tail Load for Minimum Aircraft Drag"

P E. V. Laitone's Engineering Note on ''Ideal Tail Load for Minimum Aircraft Drag, [J. Aircraft 15, 190-192 (1978)] is interesting in its use of the basic biplane equation and Munk's stagger theorem for estimating trim drag. However, there are errors in the conclusions and some of the basic assumptions of the note. First, in modern high-speed transport aircraft the contribution of compressibility drag to the total trim drag problem is very significant. The download on the tail increases the total lift that the wing must carry and if the airplane is operating near the Mach number for drag divergence the required increase of wing angle of attack will cause an increase in compressibility drag. This compressibility contribution is of the order of half of the total trim drag. On the other hand, when compressibility drag is not present the interference term in the biplane equation introduces a negative drag term which compensates to a large degree for the obvious induced drag penalties on the tail due to its download and on the wing due to the greater wing lift. Second, even with compressibility drag, trim drag is generally much less than the 5% mentioned by Professor Laitone. Figure 1 shows the variation of trim drag with center-of-gravity position for various lift coefficients and Mach numbers for a DC-8-54 aircraft. Typically, the DC-8 flies at a CL of about .35. At the original design cruise Mach number of 0.82 and at an average center-of-gravity position of about 26% of the mean aerodynamic chord, the trim drag is 2.2% of the total drag. With some consideration of aft loading cargo the average center of gravity might be moved to about 29%. The trim drag will then be 1.6%. Since the dramatic rise in fuel prices, cruise Mach number has been reduced to 0.8 to reduce compressibility drag. The trim drag penalties are then 1.4% at 26% center-of-gravity position and 0.9% at 29% e.g. position. These representative numbers are well below 5%. Only at high CL and Mach number and at far forward center-of-gravity positions can trim drag approach such high values. Third, Professor Laitone concludes that large trim drag savings could occur if only transport aircraft were designed with larger tails. An aircraft design is a matter of complete integration and a savings in trim drag would have to be weighed against the weight and parasite drag penalty of the larger tail. If we accept the possibility of a 1% decrease in induced drag from the zero tail load case with tail upload this corresponds to something like a 0.4% reduction in total drag since induced drag is approximately 0.4 of the total drag in cruise. Then the total trim drag gain from current practice is of the order of 2.0% of total drag. To gain this 2.0% one would have to move the center of gravity well aft and to do that would require significant increases in the horizontal tail size. Since the horizontal tail contributes about 8% of the total parasite drag or about 4.8% of the total drag it can be seen that a significant increase in this tail size would quickly

Observations on the Drag of Conical Bodies at Transonic Speeds

A study of the drag variation of conical bodies at transonic speeds in a wind tunnel and aeroballistic range has yielded some insight into wall interference phenomena arid sting effects. The drag reduction of these conical bodies, caused by wall interference near Mach 1, is similar to those severe trends previously observed on longer slender bodies of revolution. However, a transonic test section wall which can be reduced in porosity near Mach 1 (variable porosity with Mach number) appears to measurably reduce the wall interference problem. The influence of a sting on the base drag of these bodies has been demonstrated to be important, about 5 to 10%, and a sophisticated mathematical model of the transonic base flowfield has been developed. This model treats the base drag for various forebody cone angles and is valid for stings up to one half the body diameter in

On the drag of bodies of revolution at transonic speeds: PMM vol.39, n≗2, 1975, pp. 290–297

Dependence of the pattern of variation of gas parameters on the deviation of the oncoming stream velocity from sonic is established as the result of investigation of flow at great distances from bodies of revolution. This dependence makes It possible to determine the law of drag variation at transonic speeds, which is confirmed by calculations presented here. The weak effect of the oncoming stream velocity on the deviation of parameters at the body upstream of the compression shock from their values at sonic speed at infinity is a property of transonic flows, known as the law of stabilization. It was discovered experimentally and expounded in [1] for plane flows. The relation of the stabilization law to the pattern of the stream at great distances upstream of a compression shock was established in [2, 3]. In the first of these the assumption is made that the drag is weakly dependent also on the velocity at infinity, which is not supported by experimental data. The latter reveal a rapid motion of the compression shock toward the body trailing edge, when the velocity of the oncoming stream approaches the speed of sound. For constant parameters upstream of the shock the drag is affected not only by the motion of the shock itself, but also by parameters downstream of it. For the determination of the dependence of the drag of a body on the oncoming stream velocity, it is, consequently, necessary to investigate the flow downstream of the shock.

A Study on the Flow Around Bluff Bodies Immersed in Turbulent Boundary Layers : Part 1, On the Form Drag of a Normal Plate

In a flow field without pressure gradient, wind tunnel measurements of the pressure distributions on two-dimensional normal plates were carried out by eliminating the blockage effects to correlate with the characteristics of a smooth-wall boundary layer in which they are immersed. The drag coefficients are found to be expressed as a logarithmic function of h/σ up to h/σ =1.20, whereσ is the thickness of the undisturbed boundary layer at the position where the plate is mounted. Further, a correlation is obtained between the variation of form drag and the plate height h, which is analogous in form to the law of the wall of a boundary layer velocity profile. A method of calculating the pressure distributions on the front surface of the normal plate is proposed to analyse with the aid of a free-streamline theory. The method involves four parameters, however, which must be determined experimentally. The velocity field is integrated to construct a flow pattern for the purpose of comparing with one obtainable by the present analytical method.

Flow over Rectangular Cylinders Immersed in a Turbulent Boundary Layer : Part 1, Correlation between Pressure Drag and Boundary-Layer Characteristics

Measurement of the pressure distribution on the two-dimensional rectangular cylinders are correlated with the characteristics of a smooth-wall turbulent boundary layer in which the cylinders are immersed. The contribution of the shear stress on the horizontal upper surface of the cylinders to the total drag is estimated to be a few per cent at most over the entire range of the width-to-height ratios tested. For flows with zero pressure gradient, correlations are obtained for the variation of pressure drag with the height of the cylinder h, which are analogous in form to the law of the wall for the boundary-layer velocity profile. The coefficients of the law of the wall for the drag are functions of simply the width-to-height ratio of the cylinder. This law of the wall is valid up to h/σ = 1.37, where σ is the thickness of the boundary layer at the location of the cylinders. The contribution of the base pressure to the pressure drag coefficient is found to be sensitive to the width-to-height ratio of the cylinders, while that of the pressure on the upstream face is almost constant over the entire range of the width-to-height ratios treated in this investigation.

Measurements of plasma velocity distributions in free-burning DC arcs up to 2160 A

An experimental technique is described from which plasma velocity distributions have been determined. The technique consists of dropping a line of ball bearings of 3, 4 or 5 mm through a horizontal arc and recording the horizontal deflection of the balls by allowing them to strike a carbon paper. Multiple drops through repeated arcs enabled a deflection curve to be compiled. This curve was then subjected to an Abel inversion so that the radial variation of aerodynamic drag on the balls could be determined. By iterative techniques it was then possible to calculate a plasma velocity distribution compatible both with the Reynold's number and the radial deflection profile.A comparison with Wienecke's results obtained using photographic techniques on a 200 A arc showed good agreement, although the maximum deflection recorded was less than 3 mm with balls of 3 mm diameter. It was not possible to increase the deflection resolution by using smaller balls, since the scatter in striking position even in the absence of an arc increased unacceptably for balls of 2 mm diameter.An examination of the validity of the assumptions involved and associated errors is included. In particular the disturbing influence of the ball within the plasma is considered to be small. A more serious difficulty, pointed out by Kimura and Kanzawa concerns the difficulty of assigning the effective temperature and Reynold's number which determines the drag coefficient, since the ball and plasma boundary layer are necessarily at different temperatures. It is argued that the error involved in assigning the undisturbed plasma temperature is small.The overall error in the velocity distributions, which reach to 1500 m s−1 for the 2160 A arc, is considered to be about ±11%.

Behavior to wind action of angle and T bars on H. V. lattice structures

Dynamical behavior of T section is studied to determine whether vibrations occur under the aerodynamic action of wind. Two kinds of vibrations due to wind forces may occur and both have been investigated: 1) self-excited vibrations due to lift and drag variations and 2) forced vibrations self-controlled through vortex shedding.

Behavior to Wind Action of Angle and T Bars on H. V. Lattice Structures

Dynamical behavior of T section is studied to determine whether vibrations occur under the aerodynamic action of wind. Two kinds of vibrations due to wind forces may occur and both have been investigated: 1) self-excited vibrations due to lift and drag variations and 2) forced vibrations self-controlled through vortex shedding.

Vertical Wind Component Estimates up to 1.2 km above Ground

Vertical wind components were computed up to 1.2 km from 37 wintertime and 10 summertime balloon observations between 0900 and 1200 local time utilizing the accurate and high-resolution cinetheodolite/Jimsphere system. The mean ascent rate of the Jimsphere was computed from all observations taken on a particular day. The ascent rate was found to be 5.16 m sec−1 for the winter and 5.10 m sec−1 for the summer months. The individual variations of a given observation from the mean ascent rate were assumed to be the vertical component. Variations in balloon ascent caused by variation in drag, anomalous variation in atmospheric density, balloon response to the wind, and aerodynamically induced motions are discussed. Vertical wind components ranged from 10–25 cm sec−1 in a stable atmosphere and 55–100 cm sec−1 under unstable conditions depending on wind speed.

Influence of Secondary Flow on Drag Force

An experimental investigation was made to determine the axial variation of drag on a finite length circular cylinder with end plates and immersed in a linear velocity gradient flow. The drag coefficient for an incremental length of cylinder was found to vary from a minimum where the velocity was greatest to a maximum where the velocity was least. The force acting over the full cylinder length was found to be greater than that calculated for a uniform flow at the average velocity over the cylinder length. The pressure coefficient was found to differ when measured at the same velocity both in a uniform flow and a linear velocity gradient flow, a difference explained by secondary flow generated by the stagnation pressure gradient on the leading edge of the cylinder. A drag coefficient parameter was defined and found to increase uniformly as the length-to-diameter ratio, L/d , increased to a value of about seven; past this value the drag coefficient parameter was found to decrease.

Aerodynamic relationships inherent in Newtonian impact theory.

Aerodynamic relationships are derived which are inherent in Newtonian impact theory. Some of these relationships are independent of the particular body configuration and some depend only on the projected area of the body. The expressions derived are in a generalized form and apply to any coordinate system. In addition, they are applicable to any threedimensional configuration and for any attitude, subject to the limitations of Newtonian impact theory. The generalized expressions are applied to specific cases: two-dimensional, axisymmetric, and general three-dimensional configurations. In addition to the basic relationships, differential equations defining the drag (and, hence, lift and side force) variation with attitude as a function of the projected area are derived, and the lift-to-drag ratio is shown to be proportional to the rate of change of the drag coefficient. Finally, a comparison of the theory with experiment shows a good correlation.

The form drag of two-dimensional bluff-plates immersed in turbulent boundary layers

Measurements of the distributions of pressure on a bluff flat plate (fence) have been correlated with the characteristics of the smooth-wall boundary layer in which it is immersed. For zero pressure-gradient flows, correlations are obtained for the variation of form drag with plate heighthwhich are analogous in form to the ‘law of the wall’ and the ‘velocity-defect law’ for the boundary-layer velocity profile. The data for adverse pressure-gradient flows is suggestive of a ‘law of the wake’ type correlation. Pressures on the upstream face of the bluff-plate are determined by a wall-similarity law, even forh/δ &gt; 1, and are independent of the pressure-gradient history of the flow; the separation induced upstream is apparently of the Stratford-Townsend type. The effects of the history of the boundary layer are manifested only in the flow in the rear separation bubble, and then only forh/δ &gt; ½. The base pressure is also sensitive to free-stream pressure gradients downstream of the bluff-plate. The relative extent of upstream influence of the bluff-plate on the boundary layer is found to increase rapidly ash/δ decreases. One set of measurements of the mean flow field is also presented.