Michael Scheurlen

Computation of Turbulent Evaporating Sprays: Eulerian Versus Lagrangian Approach

A new Eulerian model for turbulent evaporating sprays is presented. It comprises droplet heating and evaporation processes by solving separate transport equations for the droplets temperature and diameter. A Lagrangian approach, which we have discussed in detail on other occasions, is used in comparing the results of the new method. A comparison with experimental data shows that both approaches are successful in predicting the main features of turbulent evaporating sprays

An Overall Correlation of Film Cooling Effectiveness From One Row of Holes

Film cooling effectiveness of a single row of cylindrical holes on a flat plate was analyzed. It was found, that the flow can be divided into two typical regimes along the downstream distance. Near the ejection location a complex flow domain of cooling film formation with strong 3-D character was recognized. Further downstream a domain of a diluting cooling film with 2-D character was identified. An analytical solution for the film cooling effectiveness along the downstream distance was derived in the 2-D regime. Based on literature data, correlations for the formation length, i.e. the length of the 3-D domain, and the corresponding film cooling effectiveness at the start of the 2-D film were developed. These correlations provide the initial conditions of the analytical solution of the 2-D film flow. A damping function was introduced to connect the two regimes and to model the lateral averaged film cooling effectiveness distribution within the 3-D flow domain. From this, a correlation was established, taking into account the full set of parameters, which was presented in an earlier study [1]. The correlation was tested over a wide range of parameters, and an error estimation is given to demonstrate the quality of the correlation.Copyright

CFD based sensitivity study of flow parameters for engine like film cooling conditions

A standard CFD code with two-layer k-e-model was used to calculate film cooling effectiveness of flat plate test cases. Experimental data from the literature were taken to perform extensive validation of the code for film cooling effectiveness prediction. Emphasis was put on injection of cooling gas through one row of cylindrical holes in the streamwise direction. Blowing ratio, density ratio, blowing angle, pitch, and hole length to diameter ratio were varied in a wide range. It was found that the code is well suited for the prediction of lateral averaged film cooling effectiveness for common film cooling conditions. A similarity analysis is presented for the prescribed film cooling problem to isolate the influence parameters of flow properties and geometry. A reduction of the parameters of influence was achieved using physical implications. The magnitude of the remaining parameters was compared for literature reported experimental results and gas turbine applications. It was found that experimental realized Reynolds and Eckert numbers are mostly far from turbine engine conditions. Therefore the validated CFD code was used to extrapolate the experimental configuration to engine like conditions. It was found that the examined Reynolds and Eckert numbers had no significant impact on lateral averaged film cooling effectiveness. It is hence possible to present a reduced but complete set of the governing influence parameters on the discussed film cooling problem.Copyright

Correlation of Film Cooling Effectiveness From Thermographic Measurements at Engine Like Conditions

Adiabatic film cooling effectiveness on a flat plate surface downstream of a row of cylindrical holes is investigated. Highly resolved two dimensional surface data were measured by means of infrared thermography and carefully corrected for local conduction and radiation effects [1]. These locally acquired data are laterally averaged to give the streamwise distributions of the effectiveness. An independent variation of the flow parameters blowing rate, density ratio, and turbulence intensity as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The influences of these parameters on the laterally effectiveness is discussed and interpreted with the help of surface distributions of effectiveness and heat transfer coefficients presented in earlier publications [1, 2]. Besides the known jet in cross-flow behavior of coolant ejected from discrete holes, these data demonstrate the effect of adjacent jet interaction and its impact on jet lift-off and adiabatic effectiveness. In utilizing this large matrix of measurements the effect of single parameters and their interactions are correlated. The important scaling parameters of the effectiveness are shaped out during the correlation process and are discussed. The resulting new correlation is designed to yield the quantitatively correct effectiveness as a result of the interplay of the jet in crossflow behavior and the adjacent jet interaction. It is built modularly to allow for future inclusion of additional parameters. The new correlation is valid without any exception within the full region of interest, reaching from the point of the ejection to far downstream, for all combinations of flow and geometry parameters.Copyright

Heat Flux Reduction From Film Cooling and Correlation of Heat Transfer Coefficients From Thermographic Measurements at Engine Like Conditions

Heat transfer coefficients and the resulting heat flux reduction due to film cooling on a flat plate downstream a row of cylindrical holes are investigated. Highly resolved two dimensional heat transfer coefficient distributions were measured by means of infrared thermography and carefully corrected for local internal testplate conduction and radiation effects [1]. These locally acquired data are processed to lateral average heat transfer coefficients for a quantitative assessment. A wide range variation of the flow parameters blowing rate and density ratio as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The effects of these dominating parameters on the heat transfer augmentation from film cooling are discussed and interpreted with the help of highly resolved surface results of effectiveness and heat transfer coefficients presented earlier [2]. A new method of evaluating the heat flux reduction from film cooling is presented. From a combination of the lateral average of both the adiabatic effectiveness and the heat transfer coefficient, the lateral average heat flux reduction is processed according to the new method. The discussion of the total effect of film cooling by means of the heat flux reduction reveals important characteristics and constraints of discrete hole ejection. The complete heat transfer data of all measurements are used as basis for a new correlation of lateral average heat transfer coefficients. This correlation combines the effects of all the dominating parameters. It yields a prediction of the heat transfer coefficient from the ejection position to far downstream, including effects of extreme blowing angles and hole spacing. The new correlation has a modular structure to allow for future inclusion of additional parameters. Together with the correlation of the adiabatic effectiveness it provides an immediate determination of the streamwise heat flux reduction distribution of cylindrical hole film cooling configurations.© 2002 ASME