An experimental study is described to investigate the negative effects of the tip clearance gap on the aerodynamic and acoustic performance of axial turbomachines. In addition to the increased broadband levels reported in the literature when the tip clearance is enlarged, significant level increases were observed within narrow frequency bands below the blade passing frequency. Measurements of the pressure and velocity fluctuations in the vicinity of the blade tips reveal that the tip clearance noise is associated with a rotating flow instability at the blade tip, which in turn is only present under reversed flow conditions in the tip clearance gap. A turbulence generator inserted into the tip clearance gap is found to be effective in eliminating the tip clearance noise and in improving the aerodynamic performance.

Experimental study of tip clearance losses and noise in axial turbomachines and their reduction

Prediction of the circumferential distribution of film thickness in horizontal and near-horizontal gas-liquid annular flows

Prediction of the effects of liquid viscosity on interfacial shear stress and frictional pressure drop in vertical upward gas–liquid annular flow

Fused Deposition Modeling is an Additive Manufacturing technology able to fabricate prototypes, tooling and functional parts without geometrical complexity limitations Despite of the potential advantages of this technology, a limiting aspect of its industrial diffusion is the obtainable accuracy The literature highlighted that significant deviations from the nominal values are observed: these deviations are not constant over all the part surfaces but strictly depend upon the process parameters, ie the layer thickness and the deposition angle This involves poor surface quality: the parts could not satisfy the design specifications nor assure the functionality and the assembly fit with other components The aim of this work is the development of a design for manufacturing methodology able to improve the dimensional accuracy obtainable by this technology It operates in the design model step performing a virtual model preprocessing: an anisotropic offset is applied to the surfaces, defined by a mathematical formulation, in order to compensate for the abovementioned dimensional deviations This way, without to eliminate the physical sources of the errors, it is possible to obtain a part with dimensional values very close to nominal ones This method does not require any additional resources for its application such as preliminary artifact construction and measurements A design for manufacturing to improve FDM part accuracy is proposedA redesign of the solid allows compensating for the dimensional deviationThe model surfaces are modified by means of an anisotropic offsetThe proposed method is applied to parts defined by a mathematical formulationThe method is validated through the application to three mechanical components

Design for manufacturing of surfaces to improve accuracy in Fused Deposition Modeling

Tip clearance noise of axial flow fans operating at design and off-design condition

The effects of tip clearance on the noise of low pressure axial and mixed flow fans

Air/water two-phase flow performance of a centrifugal pump was investigated for five kinds of closed impellers, each of which has a different outlet or inlet blade angle The results showed that (1) sudden pump head degradation due to gas accumulation in the impeller occurs at a lower air flow rate with increasing inlet or outlet blade angle of the impeller; ( 2 ) the pump head remains high even under the condition of gas accumulation when the impeller has large blade outlet angle These results are qualitatively discussed including numerical calculations of one-dimensional two-phase flow

Air-Water Two-Phase Flow Performance of Centrifugal Pump Impellers with Various Blade Angles

Noise generated by low pressure axial flow fans, III: Effects of rotational frequency, blade thickness and outer blade profile

Noise generated by low pressure axial flow fans, II: Effects of number of blades, chord length and camber of blade

Fluid forces and moment acting on a blade of the Darrieus-type runner were measured in addition to the blade performance The characteristics for various type of blades were evaluated from the measured data with theoretical considerations in an inviscid flow Some features of those characteristics, including the dynamic effects caused by an unsteady relative flow around the Darrieus-blade, are shown in the present paper For high efficiency, a noncambered thin blade with relatively long chord length is recommended Its characteristics are high lift slope, high lift at zero angle of attack and relatively low drag in a wide no-stall region of attack angles It should also be set tangent to the runner pitch-circle at the 50% chord point of the blade

Yasuo Takamatsu

Papers

The effects of tip clearance on the noise of low pressure axial and mixed flow fans

Air-Water Two-Phase Flow Performance of Centrifugal Pump Impellers with Various Blade Angles

Noise generated by low pressure axial flow fans, III: Effects of rotational frequency, blade thickness and outer blade profile

Noise generated by low pressure axial flow fans, II: Effects of number of blades, chord length and camber of blade

Experimental studies on a preferable blade profile for high efficiency and the blade characteristics of Darrieus-type cross-flow water turbines