Momentum Exchange Mechanism Research Articles

Shaping of an ion cloud's velocity field by differential braking due to Alfvén wave dissipation in the ionosphere, 1, coupling with an infinite ionosphere

We study the interaction of a plasma cloud, jetting across the geomagnetic field with the surrounding ionosphere. The cloud is assumed of finite extension in the direction normal to both the direction of motion and the magnetic field, while the ionosphere is considered a collisional anisotropic magnetized plasma. It is shown that two main mechanisms contribute to the cloud's braking: momentum exchange with the ionosphere via Alfv'n waves and momentum dissipation due to resistive currents. Due to the finite size of the cloud a differential braking of the different transverse harmonics of the Alfv'n wave appears when the momentum exchange mechanism is dominant. The result is a sharpening of the cloud's velocity field.

Measurements of Mean Velocity and Mass Exchange in a Separated Recirculating Flow

Experimental measurements were taken in a closed, recirculating, turbulent separated flow. The experiments were made to elucidate the mass and momentum exchange mechanisms between the throughflow and the recirculating flow in a combustor that had previously been developed for burning heavy fuels without a flame tube. Mean velocity measurements are presented for the cold flow field and these are used to derive a detailed streamline pattern. The three-dimensional shear layer surface that divides the recirculating flow from the throughflow is analyzed in detail and the variation of momentum exchange coefficient along its development length is derived. Mass exchange data show that the variation of mass transport along the mixing layer is similar to the variation of momentum transport. Overall features of the exchange processes are shown to be similar to those in simple two-dimensional, nonducted mixing flows if allowance is made for the three dimensionality of the present layers. However, it is also shown that there are significant quantitative differences between the two types of flow. The overall mass exchange rate between the two flow regions was found to be one-third of the mass rate supplied to the combustor and this is a typical figure for conventional designs.