Joao marcio Pinto paulon

Experimental investigations brought to light the possibilities of broadening the operating range of axial flow compressors by means of outer wall casing treatments such as grooves, honeycombs or cavities. The industrial use of these techniques is however limited by uncertainties on the effectiveness of these treatments as, while they are very beneficial in some cases, they deteriorate the performance of the machine in some others. A theoretical investigation has been conducted on the flow field in cavities most commonly used, and laws for determining the groove depth have been established which account for the surge margin improvement obtained in some cases and make it possible to dismiss inefficient geometric configurations. A comparison between theory and experiment is presented, based on test results published in the literature and on an experimentation on two industrial compressors.

A method is presented for experimental data verification on axial supersonic compressors. The actual data are submitted to thoroughly analyzed validity criteria and then accepted, corrected or rejected. An example of experimental results obtained on a rotating supersonic cascade and the final processed data are also shown.

A single, isolated, test axial compressor rotor in a constant section annular duct is used for determination of off-design pressure losses. The results obtained are interpreted by means of loss coefficients and description of the flow field is deduced from a simplified actuator theory that takes into account pressure losses. Rotor stall limit is interpreted as that limit mass flow rate for which no continuous solution of the equations can be obtained. Unstable operations that take place for mass flow rates smaller than the stall limit are shown to be either rotating stall or wall separation, according to the shape of the downstream pressure profile. Experiments on the rotor confirm validity of these assumptions.

Industrial pumps are generally used in a wide range of operating conditions from almost zero mass flow to mass flows larger than the design value. It has often been noted that the head-mass flow characteristic, at constant speed, presents a negative bump as the mass flow is somewhat smaller than the design mass flows. Flow and mechanical instabilities appear, which are unsafe for the facility. An experimental study has been undertaken in order to analyze and if possible to palliate these difficulties. A detailed flow analysis has shown strong three-dimensional effects and flow separations. From this better knowledge of the flow field, a particular device was designed and a strong attenuation of the negative bump was obtained. Nomenclature D volume flow rate, m .sec" G gravity constant, 9.81 m.sec" Η total head, m R outer radius, m U peripheral velocity, m.sec" δ flow coefficient μ total head coefficient

Results of an experimental research on the comparison of flow patterns in linear and annular, fixed and rotating supersonic blade cascades are presented. The fixed plane cascade and the fixed annular cascade give very similar results at low back pressure and the flow configuration (Schlieren pictures) and the pressure distributions are those given by theoretical calculations. In the rotating cascade the fully started supersonic regime was not obtained. At high back pressure, sidewall flow separation perturbates the flow pattern in the plane cascade. In the annular setups, the flow configuration with suction side flow separation is correctly predicted by the theory.