the embodiments of the invention shown in fig1 - 4 is in connection with a conventional feedback fluidic oscillator having a power nozzle 10 which is supplied with water from a source 11 and projects a jet of water past control ports 12 and 13 into a crossover oscillation chamber 14 . the fluidic oscillator is of the type having attachment walls 15 and 16 and curved downstream walls 17 , 18 and a downwardly tapered floor f ( fig4 ) leading to an outlet throat 19 and feedback entranceways 20 , 21 . when assembled in the housing ( not shown ), the feedback ports 20 , 21 couple with feedback passages 22 , 23 to control ports 12 and 13 to constitute a conventional feedback - type fluidic oscillator . in normal operation , the power jet expands sufficiently to fill the outlet throat 19 before the interaction region and the oscillation feedback channels begin to fill . vortices are formed on either side of the water jet , but , since two vortices cannot exist simultaneously with equal intensity , one vortex becomes dominant , and the jet or power stream will be diverted against the opposite wall . assuming it is against the sidewalls 17 , the water flows along the sidewall 17 and through the exit aperture 19 exiting to the right in fig1 . at the same time , fluid enters the feedback entranceway 20 and feedback passage 22 to direct a control signal through control port 12 to cause the jet to detach from attachment wall 15 and switch jet or crossover to the opposite side to repeat the process . thus , the jet of water sweeps in the outlet apertures 19 , right and left , back and forth as is well known in the art . pin p 1 and socket so lock the oscillatory unit in a housing ( not shown ). all units and component parts are preferably made of molded plastics , but metal moldings are within the scope of the invention . the present invention is directed to the air inlet port 25 and the structure of the surfaces downstream thereof . referring now to fig2 the outlet comprises a pair of diverging sidewalls 30 , 31 which , structurally , define the limits of the sweeping jet of water and a top wall ( top wall not shown ) and bottom wall which contain air inlet port 25 . in this embodiment of the invention , the ramp r , starting from the downstream end de of the outlet and tapering down towards the air inlet hole 25 and terminating at the air inlet , enhances air entrainment . it has been found that without the ramp r , the entrainment of air almost ceases when the nozzle was immersed beyond a certain depth . air entrainment was brought up to satisfactory levels by adding the ramp r . the following table shows the vacuum generated by adding the ramp . the tests were run at 15 psi at a depth of 28 ″: as is readily seen from the above , there is a range of ramp angles beyond which the vacuum decreases . this technique can be used for any type fluidic oscillator or even a jet - type spa nozzle to induce entrainment . referring now to fig5 a - 5e , a fluidic oscillator of the inertance - loop - type is shown . in this type of fluidic oscillator , an interaction region ir having an upstream end and a downstream end . a power nozzle pn at the upstream end projects a jet of water into the interaction region ir . first and second control ports cp 1 and cp 2 at each side of the upstream end of the interaction region ir and at each side of the jet of water projecting into the interaction ir by the power nozzle pn are interconnected by a continuous inertance loop cl . the inertance loop cl may be varied in length ( or include a variable fluidic circuit component ) to vary the frequency of oscillation . the interaction region is defined by a pair of diverging sidewalls sw 1 , sw 2 , diverging floor and ceiling walls fw and cw , with the upstream end of the diverging sidewalls sw 1 and sw 2 being connected directly to the upstream wall forming the control ports cp 1 , cp 2 , respectively . mounting flange mf and mounting bezel mb are provided for mounting in the spa tub . in operation , the water jet leaving the power nozzle pn interacts with the inertance loop cl to cause the jet of water to oscillate back and forth between the sidewalls s 1 and s 2 at a frequency determined by the continuous inertance loop cl , and the oscillating frequency is essentially proportional in the flow of water through the power nozzle pn . the higher the flow rate , the higher the frequency . an air input port ap is positioned just downstream of the control port cp 1 and cp 2 and has a protrusion pt on a downstream side thereof . this downstream structure pt enhances air entrainment . in some embodiments , such as in the embodiment shown in fig5 a - 5e , an optional splitter s ( shown in dash lines ) can be used to separate the two extreme output jet positions and provide alternating slugs of water for different massaging effects . these embodiments show the entrainment port located immediately downstream of the control ports cp 1 , cp 2 which , in contrast to the earlier embodiment , which shows the invention relative to the crossover - type fluidic ( where the output jet flows in opposite directions to the jet exiting from the power nozzle ). the arrangements shown in fig5 a - 5e , 6 and 7 can be used or without the splitters . these configurations show the entrainment port protruding into the flow by different amounts . when the entrainment port was flush with the floor , the vacuum generated was low , approximately 9 inches of water , while with the port protruding about { fraction ( 1 / 32 )} of an inch , the vacuum was 100 inches of water . while preferred embodiments of the invention have been shown and illustrated and described in detail , it will be appreciated that many modifications , adaptations and changes can be made to the invention without departing from the basic spirit and scope of the present invention .
an air entrainment spa nozzle having a jet of water which passes over an air entrainment port with the air entrainment port having a downstream structure which enhances the air entrainment . in one embodiment , the air enhancement structure is a ramp which extends in a downstream direction from the air entrainment port . in another embodiment , the air entrainment port projects or protrudes into the jet of water by a predetermined amount .