10-05-2014, 04:13 PM
Novel Fluidic Diode for Hybrid Synthetic Jet Actuator
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ABSTRACT
This paper deals with a new design of a hybrid synthetic jet actuator (HSJA), which is based
on a novel fluidic diode. Two fluidic diodes were tested using pressure-drop measurements
with air as the working fluid, and their diodicities were evaluated. A greater diodicity was
achieved with the new diode design. Two outlet nozzles of the HSJA were tested (shorter
and longer), and the velocity resonance curves were evaluated using hot-wire measurements
at the outlets of the nozzles. Volumetric efficiency of the HSJA was evaluated as function of
the operating frequency. The greatest efficiency was achieved at the second resonant
frequency of the actuator with the longer nozzle. [DOI: 10.1115/1.4024679]
Introduction
Synthetic jets (SJs), or zero-net-mass-flux jets, are fluid flows
generated by the pushing and pulling of the fluid from the cavity
through an orifice or a nozzle so that the time mean mass flow in
the nozzle is zero. Since the end of the last century, the topic has
been intensively investigated [1–3], and many useful applications
of synthetic jets were revealed. Hybrid synthetic jets (HSJs, or
nonzero-net-mass-flux jets), which were first introduced in Refs.
[4–6], are very similar to SJs; they are, however, generated by
means of nonzero-net-mass flow in the nozzle. The applications of
both, SJs and HSJs, may be found especially in boundary-layer
separation control [7–9], jet vectoring [10], and heat transfer
enhancement [6,11–14].
There are two basic types of hybrid synthetic jet actuators that
are used for generation of HSJs: The first type combines the usual
synthetic jet actuator (SJA) and valveless pump principle. Note
that such an HSJA has a similar construction as a known valveless
pump consisting of a fluidic diode, a nozzle, and a chamber
equipped with a moving piston or diaphragm [15–20]. Unlike the
valveless pump, the jet flow from the nozzle of the HSJA issues
into ambient space where the HSJ is formed.
Hybrid Synthetic Jet Principles
As mentioned previously, hybrid synthetic jet actuators are
based on the principle of the valveless pump. Figure 1 shows two
working strokes, namely, the supply and pump (or delivery)
stroke, of the valveless pump that is operating on an incompressi-
ble fluid. In the first (supply) stroke, the piston (or diaphragm) of
the valveless pump moves left, and the fluid is sucked into the ac-
tuator cavity. A conical duct element, which was chosen as the
fluidic diode here, has a low hydraulic resistance during the
inward flow (forward direction). At the end of the supply cycle,
the fluid volume VSD is supplied into the chamber through the
diode. The fluid volume sucked into the chamber through the noz-
zle is denoted as VSN.
Experimental Results
4.1 Evaluation of the Diodicities. The experiments aimed at
evaluating the diodicities for the fluidic diodes D1 and D2 were per-
formed within the HSJA from Fig. 2. The pressure drops were meas-
ured in the forward and reverse directions of flow through the diodes
at 14 different mass flow rates in the range of 0.23–2.32 kg/h, as seen
in Table 1. The mass flow rates were measured using a Bronkhorst
EL-FLOW F-201 A-50 k-AAD-33 -V precise digital thermal mass
flow meter (manufacturer: Bronkhorst High-Tech B.V., Ruurlo, The
Netherlands) that was equipped with an M-422-19-00 -V particle filter.
To evaluate a volumetric flow rate Q from the measured mass flow
rate, the fluid temperature and the barometric pressure were measured.
Conclusion
Two fluidic diodes were studied in this paper, both with a pla-
nar design. One diode (D1) was recently developed by Kordı
́k
[37] as the labyrinth-type fluidic diode. The second diode
(D2, reference diode) was designed according to the literature as
the Tesla-type diode [29]. The functionality of both fluidic
diodes was verified using measurements of pressure drops, and
their diodicities were evaluated. The highest diodicity of D1 was
approximately Di 1⁄4 3.0 and was greater than the highest diodic-
ity of the reference diode, D2. The highest diodicity of D2 was
evaluated as Di 1⁄4 2.3, which is a significantly higher value than
the diodicity measured with the geometrically similar diode in
Ref. [29] (Di 1⁄4 1.6). The improvement in the diodicity of D2
was reached using different shapes of the diode inlet and outlet
channels. The inlet channel was sharp-edged at its entrance
and had a form of flat-walled diffuser with the angle of 7 deg
(recommended in Ref. [42]). The outlet part was designed as a
channel with large opening angle 71 deg, which works as a flu-
idic diode, too [16,18,42]. Based on numerical data from Ref.
[29], we can conclude that a lower aspect ratio of the present
diode channel may have played a certain role in improvement of
the diodicity as well.