Witte_ab_1967.pdf

Greene for reducing the raw t e s t data; the Staff of the WLCIT Hypersonic Wind Tunnel, P, Baloga, H e Mazurowski, G. J e s e y for help with the design and r e p a i r of instrumentation; the Staff of the Aviation Shop, especially Ge Carlson, H e MacDonald, Ee Dahl and A. The work discussed in this s i s was published under the sponsorship and with the financial support of the U, S

Experimental investigation of an arc-heated supersonic free jet An experimental investigation of the flow field of a highly ionized supersonic free jet was conducted in a continuous flow test facility. The total pressure ranged from 28 to 35 mm Hg, at a constant flow rate, and the atomic ion number density was approximately 101 cm3 at the exit plane. Bne-dimensional isentropic flow variables of partially ionized argon have been calculated by coupling the isentropic flow equations with the partition function method for deriving thermodynamic equilibrium properties.

However, except for the effect of an excited state (the first excited state of the ion) in the equilibrium composition equation, the thermodynamic properties calculated neglecting the excitation gave results that were within 1% of those predicted including the excitation. Ratio of Equilibrium Ionized Flow to F r o z e n - Flow Maximum gas mass flows a s a function of stagnation temperature and p r e s s u r e .

The JP E MPD a r c h e a t e r has a conical copper cathode mount whose base converged from the a f t o r cooled end of the cathode a t 45O and the 2%-thorium tungsten (cathode) rod (which r a n through the copper a b s pedestal) at crossed a bs connection. The possibility of making more than one m e a s u r e m e n t , successively, with the same probe, at a given beam working condition and probe position led to the design of the combined impact p r e s u r e , m a total s enthalpy probe and Fig. so interchangeable probe points; (2) an external coolant passage designed to surround the cal o r i m e t e r which the. Even with the stainless steel shielding provided by the probe tips, the front joint of the coolant passages melted and the stainless steel tubes had to be replaced by copper tubes of nearly the same dimensions.

This hose was connected to valve A (shown in Fig.) via a nipple in the top of the tank. The inside diameter of the impact pressure tube was chosen large enough so that a measurable thermocouple signal could be obtained from the c a l o r i m e t e r when operating the probe where the total enthalpy flux was quite small, i.e. an iron-constantan thermocouple was silver soldered to the rear end of the sensor to to obtain the wall temperature of the stagnation point.

Those probe thermocouples that were installed in the inlet and outlet pipes of the probe manifold (not shown in high quality), were magnesium oxide coated stainless steel thermocouples from the power plant supply stock, which were modified and supplied by COP. Perhaps because of the s t r a y c u r r e n t s enabled by the common anode-cathode coolant passage i a r c h e a t e r , b a r e - w i r e thermo-couples in the anode-cathode coolant passages did not provide consistent data on operating conditions.

For the LVM, the discharge is suspected to be limited to the rear (upstream) end of the ring formed by the cathode and anode, while for the HVM it is limited to an area close to the exit plane. The operation in the LVM is analogous to the case of heat addition to a gas flowing in a pipe whose output Mach number was one (choked flow) prior to the heating process. pressure caused by heat addition and to provide the increased total pressure assurance required for the sound condition to maintain a constant pressure. those observed for the LVM. Although the performance of the a r c h e a t e r and the limited probe measurements in the LVM was obtained, it became quite difficult, if not impossible, to complete a series of profile measurements in the f r e jet without being disrupted by a complete change in operating mode. transition) that also had measurable effects on the f r e jet.

Therefore, a series of modifications to the apparatus led to the installation of a boron nitride cathode shield over much of the common exposed electrode, which is shown in Fig. to g a s at a r c discharge i is the average total enthalpy, hta. In HVM, the a r c voltage, a t constant c u r r e n t , was higher for the shielded cathode t e s t s , but the heat l o s s , Q, was significantly higher, so that the net effect was to give higher average unhead total enthalpy and energy efficiency, enthalpy and energy number. e s t s .

These quantities, shown in the table, were obtained for the equilibrium thernodynamic calculations of Baum and Cann (25) which correspond to our measured values of h and plenum. However, this flexibility could be achieved in this investigation only at the cost of continued operation without the cathode shield and the uncertainty and disruption of the transition from the LVM to the HVM.

Flow

SUMMARY OF RESULTS AND SUGGESTIONS FOR FUTURE WORK

One version of the so-called Magneto-Plasma-Dynamic arc heater was used to heat the gas to medium. 2508 at the exit level and remained at approximately this value along the center line of the f r e jet, The total p r e s s u r e varied between approx. Thus, using the average total enthalpy to derive local flow field quantities in the f r e e jet, i.e.

Radial profiles of stagnation point heat t r a n s p h e r were obtained between one and twelve diameters downstream of the exit plane. With Emphasis on L a r g e F r e e-Stream Velocity Gradients and Highly Cooled Wallst1, Transactions of ASME Journ. The centerline pu measurements made in the known flow field of the cold f r e jet are shown to be valid a s long a s.

This same model of the sampling technique is then used to predict the pu probe working area in hot flow. The time elapsed to move the water from the calibrated beaker to the first surface of the water. The operating range was calculated using the modified Poiseulle relationship in which the resistance of the circuit between.

For a given probe diameter and static pressure behind the shock, pa, the actual m a s flow rate must fall below and to the right of the pump. This gas does not enter the probe as part of the gas sample, but enters the collection tank and must be withdrawn from the collected mass. To calculate the operating range of the probe for given jet conditions, it was assumed, as previously discussed, that the f r e jet character of the inviscid flow field is not radically changed by gas heating.

The solution sought was the response of the calorimeter, Qc to a n input (energy/time), (1 from the gas. 38 was typically obtained from the solution for s e v e r a l Q and one s e t of coolant flow rates as a function of WePr The applicability of the stagnation point heat flux distribution given by Lees (46) for a hemisphere has already been discussed in Section III.

They showed good agreement over the entire temperature range with the 3/4 power temperature dependence of the thermal conductivity as predicted. The F a y (38) mixture rule has the advantage of indicating the role of individual species contribution to the transport properties of the mixture, and of being readily amenable to the calculation of transport properties for cases in which a solution through the more strict. Although the mixture rule, as modified, is correct in the limits of no ionization and full ionization, the values of the transport properties in the intermediate range must be used with caution.

While the third approximation of the thermal conductivity smoothly joins Spitzer's (33) value of a t 1 atrn. The poor agreement of the second approximation with Spitzer's (33) t e r - m a l conductivity was also noticed by Athye (70), who attributed this behavior to Spitper f s (33) neglecting the contribution of the ion-ion inter. Thermal conductivity, k, and viscosity, p, are represented by the sum of the contributions from each species.

Using the Lorentz conductivity (33, p. 87) for the electron gas in the mixing rule would overestimate Spitzer. For purposes of convenience, the t r a n s p o r t properties calculated from the mixture m e a n e F a y (38) r u l e and those obtained by Voto (76), calculated by the Chapman-Enskog procedure. Two ionization effects on h e r m a l conductivity related to the coulomb cross section of the ionized species.

In hot flow f o r l a r g e x/D*, prediction of A v e r is difficult due to the dependence of A on the interaction between the shock wave and the fused viscous Payer and possible rarefaction effects. In this connection, it should also be mentioned that the possibility of somewhat retarding viscous effects in cold flow for argon a s compared to a i r appears attractive due to the y effect on the Re, -M, variation shown in ~ i g. Finally, for flat-nose probes used in argon and helium, the minimurn in (Pi)m/(Pi)I is about 2% l e s s than that for diatomic gases, and the effect of the cooled probe moves the unit p r e s u r e ratio to ' a higher Reynold's ratio. number, which is quite close to the r e s d t for the probes a t the adiabatic wall temperature in N2 and a i r.

For the current cold flow study, the corrections for (pi)m were no greater than approximately 2 0/0, or within the range of the. Both probes produced the same results within the range of the hot flow data, namely s. I£T r was the arithmetic mean temperature between the boundary layer edge and the wall.

The coefficients for the last three terms are shown in the following table, where the reference variables ( )o containing nEo assume their estimated values at a given zo (but To = 20, OOOOK. 9 ~ 1 shows that TE is a very weakly decreasing function of 8. The atom-electron ionization rate of argon given by Petscheck.