Downstream Angle Research Articles

Experimental Study of the Scattering of Sound by Flowing Turbulence

The method used in experimental study of the scattering of sound by sound reported earlier [J. Acoust. Soc. Am. 27, 1002(F3) (1955) and National Advisory Committee for Aeronautics Contract NAw-6405 report, March 23, 1955] is applied in a corresponding investigation of scattering of sound by a turbulent flow. The turbulent region is a “sheet” jet emanating from a diffuser. A monochromatic ultrasonic beam is passed through the sheet, and scattered energy having a continuous frequency spectrum is measured on the back side of the sheet. The angular distribution for various frequencies is measured. It is found that the angular location of the maxima of scattering can be predicted from a simple Doppler shift calculation assuming that the turbulent velocity field is not changing with time. In fact, the angle of a scattering maximum with frequency f0 (1 + Δ) is obtained from sin θ = [Δ/M (1 + Δ)], where M is the Mach number of the flow. The angle of scattering θ is positive for downstream angles, negative for upstream angles. Our work is essentially directed toward the experimental verification of these simple theoretical predictions. The relation above has been checked for various values of Δ and M with fairly good agreement between predicted values and experimental results. [Supported by Contract NAw-6405 with National Advisory Committee for Aeronautics.]

Preliminary Experiments Using Lights and Bubbles to Deflect Migrating Young Spring Salmon

Experiments to deflect young spring salmon during their night-time migration by means of a beam of light and/or a "wall" of bubbles were conducted in a canal near Courtenay, B.C. By use of hoop nets it was discovered that under natural conditions no significant difference existed in the respective catches of the spring salmon underyearlings moving downstream on either side of the canal. A significant difference was obtained, however, when a narrow beam of light was directed into the water at a downstream angle in front of one net. A reduction to about one-third the expected catch resulted with either continuous or flashing light. The "wall" of bubbles, in a similar position, did not reduce the catch.Cut-throat trout fry and hatchery-reared Kamloops trout fingerlings were not deflected under these conditions.

A New Mechanical Analogy for the Flow of Compressible Fluid

between upstream and downstream conditions and are symmetrically placed. The nature of the relationship between complex hodograph parameter and complex velocity potential shows that similar velocity variations will occur at similar points in the complex velocity potential field when the latter has been determined in the physical plane. As the Mach Number is increased, the upstream and downstream flow angles, the stagger, and the stream deflection all decrease. The camber angle of the airfoils, given by the diameter of the hodograph circle, also decreases. The cascade solidity will decrease at the same time, since the potential gradient at any point in the physical plane is greater than the streamfunction gradient and since the ratio between the two increases with increasing Mach Number. The comparison between cascades at different Mach Numbers described here is for airfoils with cusp ends. Comparison for airfoils with rounded leading edges is possible only if the edge effect is neglected, since the relationships among angles really imply that the included angle of the leading edge will decrease along with the other flow angles in the field. The relations obtained here appear to imply those obtained by Woolard using the Prandtl-Glauert approach when the limiting case of small stream deflections is considered.