Drag coefficient

About: Drag coefficient is a research topic. Over the lifetime, 14471 publications have been published within this topic receiving 303196 citations. The topic is also known as: drag factor.

The settling velocity of mineral, biomineral, and biological particles and aggregates in water

Abstract: [1] A new equation was developed to relate the size and settling velocity of particulate matter commonly recurring in aqueous ecosystems. This equation explicitly balanced the gravitational, buoyancy, viscous, and inertial forces as in Rubey (1933) but was amended to describe in one instance both individual particles and granular aggregates with an internal fractal architecture. This approach allowed for an algebraic solution of the settling velocity, thus overcoming earlier approaches that required iterative numerical solutions. The equation was tested with mineral, biomineral, and biological suspended particles and granular aggregates from 52 existing experimental data sets, and resulted in average correlation coefficients R between 71% and 93.9%, and normilized residuals between 14.3% and 24.8% over Reynolds numbers ranging within 10−7 and 102. Accuracy of these results was generally better than for the Stokes' law, the Stokes' law modified with the Schiller-Naumann drag coefficient, and Rubey's equation. Estimated parameters ranged within observed ones, thus suggesting that the equation was robust. An analysis of the drag showed that inertial force was negligible only for biological cells (isolated cysts), whereas it contributed by not less than 5% to the drag on large mineral particles and up to 20% for biomineral and biological aggregates. Finally, a correlation was found between the organic matter content and fractal properties of granular aggregates, which were described by empirical equations proposed here for the first time. The hypothesis that the settling velocity is a function of linear and nonlinear drag, and is ultimately determined by physical characteristics as much as biological composition and internal aggregate geometry, is supported here by quantitative analyses.

Generation of a vortex chain in the wake of a Suhundulatory swimmer

Abstract: For a fish swimming at constant speed thrust must be sufficient to overcome drag. Drag of an undulating fish can differ considerably from drag observed for a rigid body and cannot be measured directly. Thrust can be calculated by applying hydrodynamic models, such as slender body theory [1], to observed kinematic patterns. Due to simplifying assumptions, shortcomings in the various applications, and probably behavioral variability, the estimated thrust coefficients (CT) range from ca. 0.5 c D to ca. 5 CD [2, 3] for animals swimming at the same Reynolds numer (c D: drag coefficient). • We present an estimate of thrust and efficiency based for the first time on the flow in the wake of freely swimming rainbow trout (Oncorhynchus mykiss Waldbaum; cf. [4, 5]). This calculation required the reconstruction of the three-dimensional vortex pattern as well as a quantification of the flow velocities, both of which are missing in studies so far available [6, 7]. We

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

Abstract: 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