Olaf Wünsch

Experimental study of polymer degassing in an agitator vessel

The present work deals with the experimental investigation of polymer devolatilization in a partial filled agitator vessel with a blade stirrer focusing on film degassing. The apparatus generate a wiped melt film on the barrel wall and a rotating melt pool at the stirrer blade contributing to mass transfer. A model substance system consisting of high-viscous polydimethylsiloxane as polymer and 1,1,2-trichloro-1,2,2-trifluoroethane as volatile is used. The driving force for the degassing is provided by reducing the partial pressure in the gas phase with a gas flow of nitrogen. The concentration of volatiles in the melt is measured by thermogravimetric analysis. The stripped volatiles were recovered and weighted by use of cold traps. The results are evaluated with models based on the penetration theory and surface renewal theory. Experimental measurements indicate that the gas-side mass transfer resistance cannot be neglected. Possible sources of inaccuracy in the execution of degassing studies and their influence on the results are discussed.The present work deals with the experimental investigation of polymer devolatilization in a partial filled agitator vessel with a blade stirrer focusing on film degassing. The apparatus generate a wiped melt film on the barrel wall and a rotating melt pool at the stirrer blade contributing to mass transfer. A model substance system consisting of high-viscous polydimethylsiloxane as polymer and 1,1,2-trichloro-1,2,2-trifluoroethane as volatile is used. The driving force for the degassing is provided by reducing the partial pressure in the gas phase with a gas flow of nitrogen. The concentration of volatiles in the melt is measured by thermogravimetric analysis. The stripped volatiles were recovered and weighted by use of cold traps. The results are evaluated with models based on the penetration theory and surface renewal theory. Experimental measurements indicate that the gas-side mass transfer resistance cannot be neglected. Possible sources of inaccuracy in the execution of degassing studies and their in...

Integral Surface Analysis of Vortical Lobed NozzleFlows

In many industrial and aerodynamical applications the mixing of flows is an essential part of the processes or work principles. In particular, mixing of the hot engine exhaust flow with the colder bypass air stream is a research topic in military aircraft design. Besides other concepts lobed nozzles are often applied in order to increase the mixing of hot and cold air and, thereby, to enforce the decreasing of the exhaust jet core temperatures lowering the infrared signature of the flight vehicle. In the present study the flow field generated by generic lobed nozzles is considered. Focal points of this work are generated vortical flow structures and their complex interaction in dependence of geometry variations of the lobes. Especially, the spreading of the vortices and the behaviour of the core part is examined in regard to the objective to derive order parameters which might be useful for the design of better mixing devices. This study is based on numerical flow simulations using a standard finite volume flow solver. Incompressible laminar flows at low Reynolds numbers are simulated addressing the fundamental physical mechanisms of vortex interaction, destructive shearing flows and vortex reorganisation and reconnection in the wake field of lobed nozzles. This work concentrates on the analysis of given numerical flow simulation results and it mainly addresses the benefits of flow field investigation by using integral surfaces of primitive and derived vector fields. The interaction of stream dividing velocity and vorticity integral surfaces is investigated. Enforced topological structure change and related diffusion processes are revealed by the topology of vortex sheets. Cutting the integral surfaces helps to elucidate special flow situations at distinct flow regions.

Flow Control of a Rotating Cylinder by the Use of a Structured Surface: A Visualization of Flow Structures

Within the present numerical investigation different spherical grooves are applied to a circular cylinder. By the use of the overset grid method a spinning of the cylinder is combined by an in flow from a radial direction to simulate the flow around a rotating cylinder. The cylinder based Reynolds number is set to a fixed value of Re = 1:34 x 10^5. To determine the influence of the surface structure the groove geometry is varied. As a result, governing flow structures in and around an array of spherical grooves can be observed.

Numerical Investigation of the Detaching Vortical Flow at Rotating Cylinders with Thom Discs

Due to the high cost pressure in the field of aviation, the further increase in effciency is in the focus of development. Nowadays, airfoils are highly developed and optimized. Thus, new sophisticated approaches, additional configurations and physical effects at lift generation devices have to be explored in order to further reduce drag and significantly increase lift. Focal point of these considerations is the Magnus effect, in which rotating cylinders generate a lift force. This has already been investigated in the past, in particular, different kinds of surface roughnesses, special rotor geometries, ratios of circumferential speed velocity to free stream velocity, or the effect of end plates have been considered. The Scottish engineer A. Thom achieved a significant increase of the performance by adding so called Thom discs coaxially and equidistantly mounted on the cylinder. Investigations of the Thom disc rotors (Thom rotors) have shown a maximum of the lift to drag ratio epsilon for the circumferential cylinder velocity to freestream velocity alpha = 2. Most of the conducted experimental studies have only delivered integral force values. However, detailed insights in the structure of the flow field are still missing.

Laminar Fluid Flow with Complex Material Behavior in Devices of Mechanical Engineering

The paper deals with the numerical simulation of highly viscous, non-Newtonian fluids in apparatus of mechanical engineering. Differential constitutive equations are used to approximate real material behavior of technical fluids such as polymer melts. The models consider shear-thinning viscosities, normal stress differences and other elastic properties which affect the fluid flow. Some details of the basis of the numerical simulations are discussed. The influence of the viscoelastic behavior is demonstrated through examples of flow calculations for two and three dimensional geometries. Comparison of the present results with other experimental and numerical results from the literature shows good agreement.