Is the Weis-Fogh principle exploitable in turbomachinery?

Abstract

Weis-Fogh discovered a remarkable new principle of aerodynamic lift. Hovering wasps exploit the principle and fly with an aerodynamic performance superior in some respects to anything previously known. In this paper we address the question of whether the Weis-Fogh effect can be exploited in turbomachinery. We think the answer is yes.Normal turbomachinery design is based on the analysis of isolated cascades of blades with steady entry and exit flows. The interactions between adjacent cascades and nonuniformities of the flow are usually regarded as problems which have to be minimized. Unsteadiness gives rise to noise. In this paper we take the opposite view and examine a novel type of turbomachinery stage that depends on the interaction between rotor and stator for its normal operation. The stage exploits the Weis-Fogh principle and has the unusual property that when started from rest it generates a pressure rise without shedding any vorticity into the fluid. We argue that there may be a performance advantage for stages of this new type.Experiments were done to check the validity of the theoretical model and these are described. The results seem to show that under certain circumstances a strong rotor-stator interaction can result in an improved stage performance, and we suggest that this improvement may be due to the Weis-Fogh effect.

Review of Experimental Work in Biomimetic Foils

“…There is a penalty, though, when large LEVs develop, because there are large separation-like pressure gradients which result in large drag and lift forces. Investigation of the use of the Weis-Fogh mechanism for applications, as suggested by Furber and Ffowcs Williams [35], resulted in relatively low efficiency [121].…”

Aerodynamics — retrospect and prospect

“…The latter problem is one however to daunt even the most enthusiastic aerodynamicistthe unsteady flow of a non-Newtonian fluid in elasticallywalled tubes of varying sizes. Bird and insect flight were investigated in some detail, the latter species revealing at least one novel method of sustaining flight, the so-called 'clap and flap' techniques' 84 ' by which very high lifts can be developed. Modern aerodynamics, enriched by more than a century of research, was repaying into new and vigorous fields debts long ago incurred from hydrodynamics.…”

Vortex-Lift Mechanism in Axial Turbomachinery with Periodically Pitched Stators

“…The resulting model ship [20] can move smoothly with a maximum efficiency of about 75%. Furber and Ffowcs Williams [22] reported that the measured properties of an axial pump are improved when the gap between blade rows is reduced, implying that the improvement is caused by the Weis-Fogh mechanism. Their work, however, only considered steady potential flow.…”

“…The loading of a rotor blade depends on the circulation around the rotor blade and on the inflow velocity. In the earlier studies on the Weis-Fogh mechanism [2,5,22], the high unsteady lift generated on the wing/blade was thought to be related to the circulation around the wing and blade surfaces. Maxworthy [3], however, indicated that the circulation around a wing surface alone is actually of opposite sign to that of the shedding vortex.…”