Helmut Ciezki
German Aerospace Center
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Publication
Featured researches published by Helmut Ciezki.
45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2009
Klaus Madlener; Helmut Ciezki
For the characterization of the flow and the spray behavior of fluids, non-dimensional numbers like Reynolds numbers are generally used. Gelled fuels are shear-thinning nonNewtonian fluids, whose rheological behavior concerning the shear viscosity - shear rate dependence can be described by an extended version of the Herschel-Bulkley equation in the propulsion relevant shear rate range. For the characterization process of this fluid type amongst others a generalized Reynolds number and a critical Reynolds number are presented.
42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2006
Jens von Kampen; Klaus Madlener; Helmut Ciezki
The flow and spray behavior of various gelled fuels, which are non-Newtonian shear-thinning fluids, is presented and compared. The present publication gives an overview about rheological properties, some aspects of the flow characteristics and of the atomization behavior of investigated gels with a doublet like-on-like impinging jet injector. Different breakup modes were observed in dependence of the jet exit velocity on the obtained shadowgraph images. Furthermore they are presented in a regime diagram with the generalized Reynolds number and the Weber number as parameters. Additionally a first attempt will be given to correlate both Newtonian and gelled fluids in a common regime diagram.
44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2008
Klaus Madlener; Helmut Ciezki; Jens von Kampen; Bernhard Heislbetz; Albert Feinauer
Propulsion systems with gelled propellants combine the ability of thrust magnitude variation on demand with simple handling and storage capabilities. The present publication gives an overview about various properties of gelled propellants, which have been investigated in basic experimental setups and/or analytically. It includes rheological properties of selected gelled fuels with regard to shear strain, their flow behavior in tubes, their spray characteristics with regard to impinging jet injectors and combustion characteristics with a single injector in a pressurized chamber.
43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2007
Bernhard Heislbetz; Klaus Madlener; Helmut Ciezki
The breakup characteristics of a plane fluid sheet flowing in a gaseous atmosphere is considered theoretically for Newtonian liquids. Several approximations belonging to hydrodynamic parameters are conducted to determine the influence of fluid properties on the breakup process. Experimental data is obtained by spray experiments with a like-on-like impinging jet injector setup and compared to the theoretical results concerning critical wave lengths and breakup lengths. The experiments show a good agreement to an introduced approximation method in the case of high viscous liquids.
Journal of Propulsion and Power | 2003
Helmut Ciezki; Joachim Sender; Walter Clau-oslash; Albert Feinauer; Albert Thumann
The combustion processes of solid fuel slabs with and without boron particle addition were investigated in a planar step combustor. The study was performed under conditions of air inlet velocity and temperature relevant to ramjet applications. The highly turbulent, multiphase combustion process has been analyzed with various intrusive and non-intrusive diagnostic techniques. Gas phase temperature distributions and particle velocities as well as concentrations of various stable reaction products have been determined in order to show the movement and the combustion of the reacting particle phase in the recirculation zone and the downstream boundary layer with the embedded reaction zone. Large scale, coherent vortex structures were observed. These structures exist predominantly in the region above the hydrocarbon diffusion flame located inside the developing boundary layer and show an intense and highly turbulent mixing process. The results show dependencies of the energy release on the flow field related to the presence of reacting or non-reacting particles.
Journal of Propulsion and Power | 2012
Klaus Madlener; Helmut Ciezki
Gelled fuels and propellants are shear-thinning non-Newtonian fluids. Their dependency of the shear viscosity from the shear rate can be described with sufficient accuracy by an extended version of the Herschel-Bulkley equation in the whole rocket and ramjet propulsion-relevant shear-rate range. Additionally to the analytically determined generalized Reynolds number for fluids, which follow the extended Herschel-Bulkley equation, a method for the estimation of critical Reynolds numbers (as a phenomenological approach) is presented. Both dimensionless numbers are useful for the characterization of the flow and partially also of the spray processes of gel fluids. The results show furthermore that both the shear-thinning property and the yield stress tend to stabilize the laminar flow and thus shift the critical Reynolds number to higher values when compared to Newtonian liquids.
49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference | 2013
M. Kobald; Helmut Ciezki; Stefan Schlechtriem
This paper summarizes the investigations on the combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen (GOX) as oxidizer in a 2D slab burner with windows on two sides. High speed video data and Schlieren measurements have been evaluated to give an insight into the combustion phenomena of paraffin-based hybrid rocket fuels. The combustion flame shows a periodic, wave like structure. This behavior is noticed for different types of paraffin fuels. The values of the liquid layer viscosities are the main difference between the fuels. This affects the droplet entrainment process during combustion and also the regression rates of the fuels. Entrainment and regression rate increase for decreasing fuel liquid layer viscosity.
41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2005
Helmut Ciezki; Tobias Tiedt; Jens von Kampen; Nora Bartels
The atomization behavior of Newtonian fluids and non-Newtonian gelled fluids, which show a shear-thinning behavior, with a doublet like-on-like impinging jet injector has been investigated with the shadowgraph technique. The spray behavior of both distinct Newtonian fluids and non-Newtonian gels will be presented and compared. The experiments with Newtonian fluids of different Ohnesorge numbers have been conducted in a wide range of Reynolds and Weber numbers (60 ≤ Re ≤ 30,000 and 100 ≤ We ≤ 30,000). The different observed breakup modes are presented in a Regime diagram with Reynolds and Weber numbers as parameters. The present publication gives an overview about the actual state of the investigations and a first attempt will be presented to correlate both Newtonian and gelled fluids in one Regime diagram.
38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit | 2002
Helmut Ciezki; Ansgar Robers; Günter Schneider
The spray behavior of gelled Jet A-1 fuels has been visualized by means of the shadowgraph technique for an air blast atomizer with an annular converging coaxial air-flow and a doublet like-on-like impinging jet atomizer. For the air blast atomizer different break-up regimes can be seen with increasing momentum flux ratios for the three investigated fuel/gelling agent-mixtures. For the impinging jet atomizer the formation of a gel sheet at the intersection of both jets has been observed, from which arched ligaments separate periodically and decay further downstream.
Journal of Propulsion and Power | 2017
M. Kobald; C. Schmierer; Helmut Ciezki; Stefan Schlechtriem; E. Toson; L. T. De Luca
The combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen as an oxidizer has been analyzed in detail. Regression rate tests have been done in a two-dimensional radial microburner at the DLR, German Aerospace Center and at the Space Propulsion Laboratory. Fuel samples have been characterized by viscosity measurements, tensile tests, and a differential scanning calorimeter. Tensile tests showed significant improvement in maximum stress and elongation when polymers in low concentration were added to the paraffin samples. The values of the liquid fuel viscosities differed significantly between the selected fuels. This affected the droplet entrainment process during combustion and the regression rates of the fuels. The entrainment and regression rate increased for the decreasing fuel liquid layer viscosity. An exponential relation has been found between the liquid fuel layer viscosity and the regression rate, which can be used to predict the regression rate of new liquefying fuels by measuring their viscosity.