Investigation On Tip Leakage Suppression In An Axial Tubine By Spontaneous Tip Injection

Turbomachinery is an important power machinery used to realize energy conversionbetween the fluid and the shaft power, which occupies a very important position in theenergy and power field. The existence of the rotor tip clearance is not only resulting inworking medium leakage, which leads to power loss, more important is the occurrence ofleakage flow will influence the flow loss and heat transfer characteristics of tip clearanceand the whole flow passage in a great extent. In this study, we take the low-speed linearCascade (Durham Cascade) as research object and a passive tip leakage control method,namely, using spontaneous tip injection(STI) controlling tip leakage and its loss is studiedsystematically.First, the numerical model of single-hole spontaneous tip injection was establishedand the grid independence check and numerical model validation has been done. Theeffectiveness of controlling the tip leakage by using STI has been verified with the methodof three-dimensional numerical simulation. Compared with the no STI, the leakage withSTI was cut down5.42%and the circumferential blade load increased1.39%and theisentropic efficiency was promoted by1%-2%under the condition of inlet Reynoldsnumber is5.764×105and tip clearance is0.5％H. Passage flow field characteristics andrules of flow loss with the presence of STI were analyzed and the influence of tipclearance height and rotor inlet Reynolds number on leakage control effectiveness wasdiscussed also.Then, through a large number of example calculation, jet hole opening parameterswere discussed in detail, including the jet port aperture ratio, outlet and inlet position,outflow direction and angle, the number of jet hole etc. The general guiding principle ofopening hole has been obtained in such scale cascade. In addition, the potential applicationprospect of internal circular channel mode was studied.Then, by using the method of three-dimensional numerical simulation, several typicalfactors of real operating condition, such as incidence angle, casing wall relative motion,blade rotation and unsteady inlet have been studied with the emphasis on the cascade flow field characteristics, flow loss distribution and the leakage flow suppression effect and theblade load distribution.Finally, a small-scale low-speed wind tunnel test rig was developed and the planarflow field adjacent to the injection hole was measured under low Reynolds numbercondition (103-104) using2D-PIV technique. The detailed aerodynamic interactionbetween the STI and the tip leakage flow (TLF) under the both laminar and turbulent flowconditions in the tip clearance was presented. Based on the experimental results, theinteraction characteristics between the STI and the leakage flow was analyzed and theleakage flow control mechanism was illustrated.