Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

Particle image velocimetry study of flow near trashrack models.

Abstract: This paper provides results of an experimental study of turbulent flow near trashrack models that are comprised of an array of three rectangular bars. The bar thickness, bar depth, and center-to-center spacing were maintained constant. The flow characteristics were studied by aligning the bars with the approach flow and conducting measurements at three different approach freestream velocities. Subsequently, the freestream velocity was kept constant and detailed measurements were conducted for four different bar inclinations relative to the approach flow. For each test condition, a high-resolution particle image velocimetry (PIV) technique was used to conduct detailed velocity measurements in streamwise-spanwise planes at middepth of flow. From these measurements, isocontours and profiles of the mean velocities, turbulence intensities, Reynolds shear stress, and production term in the transport equation for the turbulent kinetic energy were obtained to study the flow characteristics around and downstream of the aligned and inclined bars. Flow characteristics near hydroelectric station trashracks are important for efficient turbine operation and reduction of fish entrainment.

Effect of fineness ratios of 0.75–2.0 on aerodynamic drag of freestream-aligned circular cylinders measured using a magnetic suspension and balance system

Abstract: The drag coefficients of freestream-aligned circular cylinders of fineness ratios of 0.75–2.0 were investigated with a magnetic suspension and balance system (MSBS). The objective was to find the critical geometry, that is, the fineness ratio at which the drag coefficient becomes the local maximum within this ratio range. The experiments were conducted using the 1-m MSBS at the low turbulence wind tunnel at the Institute of Fluid Science, Tohoku University. The drag and base pressure coefficients of various cylinders were measured. The freestream velocity was varied to produce flows with Reynolds numbers ranging from $$0.6\times 10^5$$ to $$1.0\times 10^5$$ . The drag coefficient monotonically decreases as the fineness ratio increases and no critical geometry or local maximum of the drag coefficient is found in the range we investigated. The base pressure coefficient decreases as the fineness ratio increases. The temporal fluctuations of the base pressure of the models with fineness ratios of 0.75, 1.0, and 1.2 are approximately twice as large as that of the model with a ratio of 2.0. The relationship between the fineness ratio and the drag coefficient is similar to that between the fineness ratio and the base pressure coefficient, similar to the findings of previous studies of two-dimensional bodies.

Mixing Enhancement in Compressible Base Flows via Generation of Streamwise Vorticity

Abstract: A C-type boundary-layer grid around a NACA-0012 airfoil has been generated up to a normal distance corresponding to 1=Ch D 0:06. The values of N and s are 20 and i4, respectively. This boundary-layermesh is coupled and with unstructuredand algebraicmeshes as shown in Fig. 5. Figure 6a shows the streamlines in laminar  ow with the conditions for freestream Mach number M1 D 0:5, Reynolds number based on chord RechD 5£ 10 and incidence ®D 0 deg, same as those used by Liu.4 The present results, including a small separation zone near the trailing edge, are in good agreementwith Liu.4 Figure 6b shows the isentropicMachnumbercontoursfor the turbulentcompressible owatM1 D 0:754, Rech D 3:76£ 106 , and ®D 3:02 deg. With the help of hyperbolic grid, the Baldwin–Lomax turbulencemodel has been implemented without any complex changes, such as those suggested by Turner and Jennions. The standard k–" model is used in the unstructured and algebraic grid zones. This result is in good agreement with the predictions of Kallinderis.

End-Stage Boundary Layer Transition Models for Engineering Calculations

Abstract: The paper presents some recent new data on the combined effects of pressure gradient and freestream turbulence level on the onset and length of the latter stages of the boundary layer transition process. Generalized correlations for the transition length Reynolds number are developed from considerations of the non-dimensional turbulent spot formation rate. The optimized correlation is built into a popular linear combination integral computer code to predict the growth of the transitional boundary layer in a number of practical engineering flows.

Turbine Burners: Performance Improvement and Challenge of Flameholding

Abstract: Nomenclature A = preexponential chemical rate constant a, b = mass fraction exponents in chemical rate law C = correction factor D = cavity depth E = activation energy f = frequency h = enthalpy L = cavity length M = Mach number, mixedness parameter n = Rossiter mode number p = pressure Q = fuel heating value R = universal gas constant Re = Reynolds number St = Strouhal number T = temperature t = time U = flow velocity over cavity x = position along mixing layer Y = mass fraction y = transverse position in mixing layer = ratio of specific heats = burning efficiency = ratio of convective velocity of vorticity to freestream velocity = Rossiter variable = density ! = chemical reaction rate